Biology and status of timber rattlesnake (Crotalus horridus) populations in Pennsylvania

BIOLOGY AND STATUS OF TIMBER RATTLESNAKE (CRO TAL US HORRID US) POPULATIONS IN PENNSYLVANIA

JOHN H. GALLIGAN 8£ WILLIAM A. DUNSON

Department of Biology, Pennsylvania State University, University Park, PA 16802, USA

ABSTRACT

The purpose of this study was to examine certain aspects of the life history and ecology of the timber rattlesnake (Crotalus h. horridus) in Pennsylvania, and to evaluate the reported decline in numbers of this species. The influence of commercial hunting has been considered and suggestions are made for conservation of this unpopular but intriguing snake. The previous and present abundance of rattlesnakes was first considered by a programme of interviews with commercial hunters. Visits were also made to many supposed den sites in central Pennsylvania, and to four rattlesnake hunts held in the summer of 1976. There were consistent reports of a large recent decline in the number of rattlesnakes seen and captured. These opinions of the scarcity of rattlesnakes were personally confirmed by visits to known dens. One rattlesnake den was chosen for a study on dates offirst capture in the spring, on transplantation of snakes from other localities, on movements of newly released and long-term den residents, and on rodent populations. During three consecutive springs the dates offirst capture of rattlesnakes varied only between April 23 and 30, despite marked differences in the pattern of air and ground temperature variation. Many snakes transplanted to a new den site apparently left the area almost immediately. Six out of 33 adults released were recaptured at the new den; three of these hibernated there. Only one of the 48 newborn rattlesnakes released soon after birth in the autumn was recaptured in the subsequent spring. On emergence from hibernation two rattlesnakes were tracked by radiotelemetry. They remained at the den until June, and left soon after shedding. One snake was followed to a distance 1055 m from the den over a period of 69 days. Considerable rodent food was available on the talus slopes of this den. Mice (Peromyscus leucopus) were abundant; in a 0-7 ha grid trapped for one week the population was estimated at 61/ha. Nine gravid rattlesnakes were held in the laboratory to obtain information on litter size. The average litter was seven (range 13 Biol. Conserv. (15) (1979)--© Applied Science Publishers Ltd, England, 1979 Printed in Great Britain

14

JOHN H. GALLIGAN, WILLIAM A. DUNSON

5-9) and females lost an average of41% of their body weight during parturition. The metabolic demands of pregnancy are high and females only reproduce every two, or possibly every three, years• The smallest female to produce a litter had a snout-vent length of 770 mm, and it is estimated that this animal was five years old. Positive correlations between head length and snout-vent length, and body weight and snoutvent length were found. No significant differences in these relationships between the sexes or between snakes freshly caught in different areas were noted. There was a decline in relative body weight and head length after prolonged starvation in captivity. Male rattlesnakes have significantly longer tails than females. The timber rattlesnake in Pennsylvania is rapidly approaching extinction. Prohibition of bounties, snake hunts, and commercial sale of snakes, and protection of rattlesnakes in remote areas of state and national forests would significantly enhance the prospects for survival o[ viable populations ofCrotalus horridus.

INTRODUCTION

The historic range of the timber rattlesnake (Crotalus h. horridus) was large, extending from southern Maine to the southern Appalachians, westward to Wisconsin, eastern Kansas and Oklahoma, and south in the Mississippi Valley to east Texas (Fig. 1). In Pennsylvania, in recent times it has been widespread in

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BIOLOGY AND STATUS OF TIMBER RATTLESNAKE POPULATIONS

15

mountainous areas and absent only in the southeastern corner and western edge of the state (Fig. 2). Its pre-Colonial range was probably state-wide. This snake is now declining over much of its range, as are some other reptiles. In many areas the decline is due to habitat destruction. In Pennsylvania, the rattlesnake is rapidly approaching extinction, but the major cause is hunting for commercial purposes and sport. The catching and killing of timber rattlesnakes by the public is not a new phenomenon, but higher prices for snake products, the availability of four-wheel drive vehicles, the many roads cut into remote mountain areas, and the publicity of the state's snake hunts have combined to interest more people in the activity of snake hunting. The effect of this ever-increasing number of hunters has been the extermination of many known snake den populations, and the continuous search for previously undisturbed ones.

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Large rattlesnake populations are so rare today that many newer hunters doubt that large concentrations ever existed. Older snake hunters and past publications, however, often report the existence of large numbers of snakes. Wheatley (1886) describes a den near Wilkes-Barre, Pennsylvania, where a group of men killed a few hundred rattlesnakes on a single day. Surface (1906) reported the killing of 250 rattlesnakes within a week at a den in Franklin County. More recently, Swanson (1952), Klauber (1956), and Rutledge (1958) record dens producing more than 100 specimens. Russ (1950) reported that one hunter had killed 109 during the month of May. One hunter killed 63 in a single day (Anderson, 1950). Anderson (1951) participated in a hunt at two dens, which had been hunted previously, during which 40 rattlesnakes were killed. The rapidly progressing exploitation of timber rattlesnakes has led one national

16

JOHN H. GALLIGAN, WILLIAM A. DUNSON

organisation, the Society for the Study of Amphibians and Reptiles, to list it as an endangered species in Pennsylvania (Ashton, 1976). The criterion for this endangered status was that 'without full protection throughout its range, the species could be extirpated within the next ten to twenty-five years.' Although the timber rattlesnake was one of the first rattlesnakes encountered in the New World, it has received relatively little scientific attention. Most of the ecological studies were made in the western United States because the conditions were more favourable for collecting large numbers of snakes. Although little is known specifically about the biology of C. h. horridus, the many studies made on other species offer a rich source of general information. The ecology of Crotalus viridis has been thoroughly studied. Reproduction was described by Rahn (1942), feeding habits by Fitch and Twining (1946), and mark-recapture studies were conducted by Fitch and Glading (1947) and Fitch (1949). Woodbury (1951) made an eleven-year study of Great Basin rattlesnakes at a hibernaculum near Grantsville, Tooele County, Utah. The same den was also the site of studies of overwintering, mortality and weight loss (Hirth 1966a), homing ability (Hirth, 1966b), biomass densities (Hirth and King, 1968), body temperatures (Hirth and King, 1969), dispersal patterns (Hirth et al., 1969), and mortality and weight changes (Parker and Brown, 1974). Landreth (1973) has also studied the orientation and behaviour of Crotalus atrox. The purpose of this study was to examine the status of timber rattlesnake populations in Pennsylvania. Information was obtained on life history and morphometrics and the reported decline in numbers of the timber rattlesnake was evaluated by den surveys and interviews with experienced hunters. Various management alternatives for timber rattlesnake populations in Pennsylvania are considered in relation to current regulations.

MATERIALS AND METHODS

Hunter interviews Experienced snake hunters were interviewed to determine the extent and methods of snake hunting, the uses made of captured rattlesnakes, and their opinion of the status of the rattlesnake in Pennsylvania. Snake den sites Over 15 different areas were searched for rattlesnake dens suitable for a population study. State game lands, a state forest, and a state wild area were checked in four counties in central Pennsylvania. Possible study locations were found through information gained in interviews and the use of topographic maps. When a site was chosen to be studied, it was repeatedly searched, and all snakes captured in the area were measured and marked. If the snake was a new capture or a marked snake that had not been captured in more than a month, measurements were

BIOLOGY AND STATUS OF TIMBER RATTLESNAKE POPULATIONS

17

taken of head length, total length, tail length, and body weight. Weight was taken in the field with a Chatillon hanging scale graduated in 10 g increments. Snake weights in the lab were measured with a triple beam balance accurate to 0-1 g. Head length was measured from the vertical face of the rostral scale to the posterior end of either mandible with calipers graduated in mm. To make measurements as consistent as possible, head length was taken with the snake's head resting on an object, while the index finger of the hand holding the head pushed down upon it to keep the jaws closed. To obtain a measurement of total length, the snake was gently but firmly compressed under plexiglass into a 5 cm thick piece of foam rubber in a modified squeeze box measurer (Quinn and Jones, 1974). A line was then drawn on the plexiglass with a water soluble marker, from the tip of the snake's snout down its vertebral line to the posterior tip of the last scale on its tail. A map measurer was run along the length of the line to obtain the total length. The line could then be washed off so that the box was ready to measure another snake. Following the total length measurement, the snake's tail was pulled through an appropriately sized hole on the side of the box while the plexiglass rested on the anterior end of the snake. This allowed work to be done on the posterior end without having to hold the snake behind the head for an extended period of time, and permitted one person to do all measuring and marking without assistance. Reducing the time spent holding the snake's head also reduced the chance for harm to either the researcher or the snake. Tail length was measured with a transparent ruler graduated in mm. This length was measured from the posterior tip of the cloacal plate to the posterior tip of the last scale on the tail. Snout-vent length was then obtained by subtracting tail length from total length. Snakes were sexed while restrained in the squeeze box, by probing with a thin blunt rod into either side of the cloaca towards the tail (Schaefer, 1934). The probe could be easily inserted into the invaginated hemipenis of the male for the length of eight or more subcaudal scales, whereas in the female it could not be inserted to any appreciable length. If the snake was a female, it was palpated to determine if it was gravid (Woodbury and Hansen, 1950). Captured snakes were marked by clipping off half of certain subcaudal scales with fine scissors (Blanchard and Finster, 1933). While clipping scales, the number and arrangement of subcaudal scales were recorded and noted. In addition, the dorsal pattern ofcrossbands and blotches was recorded in a drawing. The scale counts and pattern sketches were also used for individual recognition of recaptured snakes, and became more important as the scale clippings gradually healed. After being marked and measured, all snakes were released at their points of capture. Rodent trapping at a snake den

To determine the species of rodents that were available to the snakes at the primary study den (B den), a trapping programme was carried out on a four by eight grid with 15.2 m grid intervals. At each station an 8 x 9 x 23 cm folding aluminium

18

JOHN H. GALLIGAN, WILLIAM A. DUNSON

trap (H. B. Sherman Traps, Tallahassee, Florida) was set and baited with peanut butter and rolled oats. For seven days the traps were checked daily and all rodents identified, sexed, and marked by toe clippings. The number of daily captures and recaptures were then used with the Schnabel estimator to estimate the population size of the different species of rodents (Overton, 1965).

Snake release Both adult and newborn rattlesnakes were released at new den locations to determine if they would stay in the area. A total of 49 adult snakes were released at different dens at various times of the year. Forty-eight newborn rattlesnakes, the offspring of snakes held in the laboratory, were released at one den in late summer and early autumn. Forty-four of the 48 newborns were released within 48 h of their birth. All released snakes were measured and marked before being released, according to the procedure described earlier. Five of the adult rattlesnakes released in the summer of 1976 were followed for 12 h by sight. The snakes were transported to the release site in translucent nylon bags, the bags were then untied, and the snakes allowed to find their way out. Observations were made from a tree near the release point. When the snake had gone a short distance, the observer was forced to follow on foot, staying as far away from the snake as possible to minimize influencing its movements.

Telemetry In the spring and summer of 1977, a total of six rattlesnakes were followed by radio-tracking using techniques similar to those of Fitch and Schirer (1971), Parker and Brown (1972) and Brown and Parker (1976). Snakes were monitored in the field for periods ranging from two to 69 days. Two of the rattlesnakes tracked were ones which had overwintered at the den after having been released there the summer before. The four other rattlesnakes tracked were released into the study area for the first time after having been force fed a transmitter. Two of the four were males which had overwintered in the laboratory. The other two were gravid females which had been captured a few days before at a location about 60 km north of their release point. Pulsed, temperature-sensitive transmitters were used (model L, the Mini-Mitter Co., Inc., Indianapolis, Indiana). Transmitters of different transmission frequencies (ranging from 27-495 to 27.635 MHz) were placed in different animals. The effective range of the transmitters was usually less than 65 m when the snake was above ground, and much less than that when the snake was beneath ground. The receiver was a Lafayette HA-420 walkie-talkie (The Mini-Mitter Co.) converted to handle six channels. After initial reception of a transmitter signal, a directional antenna (model AF, the Mini-Mitter Co.) was used to pinpoint an animal's location by triangulation. The transmitter was powered by four 1"5 V Duracell batteries which

BIOLOGY AND STATUS OF TIMBER RATTLESNAKE POPULATIONS

19

were encapsulated with the transmitter in a polyethylene vial. The vial was sealed shut with a soldering gun. Each sealed transmitter unit was a 6.0 x 2.1 cm cylinder and weighed 16-7 g. Each snake was force-fed an encapsulated transmitter coated with vegetable shortening. The transmitter unit was palpated down the snake's esophagus and presumably lodged in the stomach or small intestine. This method had first been tried under laboratory conditions for several weeks, and was found to have no apparent effect on a large snake's ability to digest its food and to defecate. The snakes chosen to receive transmitters were over 82.5 cm in total length. Two of the rattlesnakes regurgitated their transmitters, but one of the transmitters and one of the rattlesnakes were found again. Once the transmitter was in place, the snake was either returned to its point of capture or transplanted to a specific location. Snakes not native to the area were taken to the release point in nylon snake bags placed inside a backpack. The usual procedure was to locate each snake at least once a day, and more often if the snake was moving. Snakes were not otherwise purposely disturbed except for battery changes. When a snake was located, its position was marked with flagging. Litter size To obtain information on litter size and weight loss due to parturition, seven gravid female rattlesnakes were either purchased from hunters or captured in a nonstudy area and kept in the laboratory at 25-28 °C with a 12 h light-dark cycle until they gave birth. Snakes were offered food and water and a record was kept on each snake's weight. If, after giving birth, the snake accepted food, records on its weight were continued. If a snake did not adjust to captivity, it was released. Morphometric measurements Measurements of head length, snout-vent length, tail length, and weight were obtained from 260 different rattlesnakes (130 males, 71 females, 39 newborn young, and 20 of undetermined sex). Arithmetic, semi-logarithmic, and logarithmic plots were made and simple linear regressions were done to determine what type of correlation existed between the different measurements taken. Plots and regressions were made for all snakes pooled together, and then again separately by sex. An analysis was also made for snakes from different areas to see if geographic variation was evident. The linear regression equations were tested for significant difference using the general linear test. Feeding rate Seven timber rattlesnakes, varying in snout-vent length from about 27 to 84cm, were maintained in the laboratory from the autumn of 1976 to the summer of 1977. A record was kept of their weight along with the weight of food eaten. The

20

JOHN H. GALLIGAN, WILLIAM A. DUNSON

laboratory was on a 12 h light-dark cycle, and temperature usually was 25-28 °C. All snakes were kept in 27 x 52 x 32 cm glass aquaria with plastic retreat boxes, and had 60W incandescent bulbs on top of one end of their cages. Public hunts Four of the seven organised rattlesnake hunts held in the state were attended in 1976 and hunters and local residents were interviewed. Captured snakes were examined, sexed and measured. The procedure used to gather information on the snakes was the same as described above, except that the squeeze box used for the hunts was a larger, 0.6 x 1.2 m, model that was much more efficient in handling a larger number of snakes.

RESULTS AND DISCUSSION

Area survey and den locations In order to obtain information on the life history of the timber rattlesnake and the effect of commercial and sport hunting, studies were planned for both undisturbed and regularly hunted den sites. By measuring, marking and then recapturing snakes, it was hoped that information on their growth, reproduction and movements would be obtained. However, the search for an undisturbed den proved instead to be a study of the pervasive influence of snake hunting. All of the areas examined were either extensively hunted or had only a very small population of snakes. No undisturbed den with a population large enough for a comprehensive study could be found. During 1976, over 15 different areas were checked, some only once, others repetitively, depending on how many snakes were seen and how heavily hunted the area appeared. Signs of snake hunters were usually evident in overturned rocks. The following localities were examined: Bald Eagle Ridge in Centre County, Sandy Ridge in State Game Lands 60 in Centre County, near the Tipton reservoir in Blair County, two areas on Jack's Mountain near Tuscarora State Forest in Huntingdon County, two areas in Sproul State Forest in Clinton County, and three areas in Rothrock State Forest, Huntingdon County. In the Quehanna Wild Area and adjacent Moshannon State Forest, parts of the following areas were checked: Mosquito Creek, Gifford Run, Twelve-Mile Run, Wykoff Run, Upper Jerry Run, McNerney Run, Big Spring Draft and Jerry Lick Draft. The term 'area' is used to define a location where snakes are found or were expected to be found based on information from maps or knowledgeable people. A location containing snakes may be a small outcropping of rocks only a few hundred feet wide, a whole section of mountain ridge, or a talus slope. Areas were only classified as different if they were separated by distances of more than two km or were found on different mountain ridges. The area most intensively examined included a supposed den on Bald Eagle

BIOLOGY AND STATUS OF TIMBER RATTLESNAKE POPULATIONS

21

Ridge, one o f the areas in Rothrock State Forest, one of the areas on Jack's Mountain, and the Quehanna Wild Area. Although the first three had only small rattlesnake populations, they were repeatedly examined because they were thought to be no longer hunted. The Quehanna Wild Area was examined because it had been recommended by many hunters and the Bureau of Forestry as having one of the best rattlesnake populations in the state. The Rothrock State Forest site was eventually disturbed by snake hunters, and at almost all of the areas checked in the Quehanna area and Moshannon State Forest there were signs of snake hunting. By the autumn of 1976, only two of the sites examined in the Quehanna Natural Area and Moshannon State Forest showed no apparent traces of rattlesnake hunters, and both of these had only small populations of snakes. Snakes were marked at these two locations and at the den on Bald Eagle Ridge. Finally, in the autumn of 1976, it was decided to do the transplantation and movement studies at the Bald Eagle Ridge den because of its proximity, and the availability of some data from 1975 on snake captures. Although Burger (1934) reported the hibernation of timber rattlesnakes in sand in the New Jersey Pine Barrens, there seems to be a preference for making dens in ledges and crevices along slopes with southern exposures. Presumably the southern slope is favoured because it is the side receiving the most solar radiation. Ditmars (1936) reported that timber rattlesnake dens in Pennsylvania face south, while Petersen (1970) stated that timber rattlesnake dens in Connecticut generally have southern, southwestern, and southeastern exposures, with northern exposures being avoided. In the 27 den areas that we have either examined ourselves or that have been reported to us by reliable sources and checked on topographic maps, the majority are on the slopes that face south or southwest. If the direction of the slopes of the dens are compared (a den area may have more than one slope), about 70 9/0face this direction. The remaining 3 0 ~ face either west or southeast. Although these statistics are believed to be fairly representative they are slightly biased. All of the snake hunters interviewed agreed that snake dens usually have a southern exposure and as a result they spent more time hunting such slopes. Therefore fewer dens of northern exposure may be discovered than would be if an equal effort were put into searching all slopes. Some northward facing dens have been reported by hunters although we have not had the opportunity to visit them.

Description of main study den The den designated as 'B' was chosen for further studies such as release experiments and rodent trapping. The den is located at an altitude of about 500 m on a ridge running SW to N E (Fig. 3). The den area is primarily composed of talus rock on three slopes and woodland on the fourth. The talus slopes are Pleistocene in age and are composed of Tuscarora Quartzite. These rocky slopes face south, west and north.

22

JOHN H. GALLIGAN, WILLIAM A. DUNSON

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In spring 1975, eight black racers (Coluber c. constrictor) and five adult timber rattlesnakes were captured at B den. F o u r of the black racers and two of the rattlesnakes were removed while the rest were marked and returned to the den. In spring 1976, the den was examined on 14 days for a total of 23 h. Six black racers and two rattlesnakes were captured and one rattlesnake was seen but not captured. In spring 1977, the den was examined on 43 different days for a total of 78 h. One northern copperhead (Agkistrodon contortrix mokasen), two black racers, three black rat snakes (Elaphe o. obsoleta) (one of which had been released there the previous summer), one eastern garter snake (Thamnophis s. sirtalis), and three timber rattlesnakes (all of which had been released there the previous summer), were captured. Some of the above snakes were recaptured as m a n y as seven times in a single spring.

BIOLOGY AND STATUS OF TIMBER RATTLESNAKE POPULATIONS

23

Emergence at main study den An effort was made to determine if any correlation existed between weather and the emergence of snakes in the spring. Air and ground temperatures and the initial capture dates of black racers and rattlesnakes at B den are shown in Fig. 4. Daily minimum and maximum air temperatures were obtained from the Pennsylvania State University Meteorology Department. Weekly mean minimum and maximum soil temperatures at a depth of 914mm were obtained from Dr Guy McKee of the Pennsylvania State University Agronomy Department. Although temperature measurements were not taken at the den, they were recorded less than 21 km away from it. There is no obvious relationship between air and ground temperatures, and dates of initial capture. There were often warmer periods weeks before the dates on which the snakes chose to emerge. If temperatures at which the first rattlesnake emerged in 1975 are used to predict snake emergence in 1976 and 1977, the prediction would be two weeks earlier than observed. Snakes did emerge earlier in 1976-77 but they also emerged at higher temperatures than in 1975. Snake emergence, therefore, is probably affected but not completely determined, by temperature. There are obvious evolutionary advantages against using temperature alone as a cue for emergence since occasional early warm spells are misleading indicators of the general climate. Black racers emerged earlier than timber rattlesnakes (Fig. 4). In 1975, the first black racer was captured 15 days before the first rattlesnake. In 1976, there was a 30day difference, and in 1977 it was 45 days. Vetas (1951) noted a similar relationship between the western striped racer (Masticophis t. taeniatus) and the Great Basin rattlesnake ( C. v. lutosus).

Rodent trapping at main study den Population estimates of small rodents which could serve as food for the snakes at B den were calculated from capture-recapture data. Most of the animals caught were white-footed mice (Peromyscus leucopus) but some voles (Clethrionomys gapperi) were also captured. Because white-footed mice do not usually adhere to the equal catchability assumption of the Schnabel estimator (Niles, 1976), separate estimates were calculated for white-footed mouse and vole populations. During the seven trap periods, 45 different white-footed mice were captured, and a total of 65 recaptures were recorded. The population estimate of the white-footed mice in the 0.743 ha area trapped was 45 mice with a 95 ~o confidence interval from 35 to 58. Since white-footed mice tend to be recaptured many times, the Schnabel estimate is identical to the actual number caught. Therefore, the actual population number is probably larger than the estimated one. Since only 14 different voles were captured and there were only four recaptures, a reliable assessment of their population could not be made. The vole population was estimated to be 24 animals/0.743 ha with a confidence interval from 9 to 61. The white-footed mice were captured throughout the area trapped, which ranged from areas where there was some soil between rocks to other places where no soil was

24

JOHN H. GALLIGAN, WILLIAM A. DUNSON

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BIOLOGY AND STATUS OF TIMBER RATTLESNAKE POPULATIONS

25

apparent. The voles, however, showed a more limited habitat preference. Thirteen of the 18 captures of voles were from traps set at the bottom of the slope near the woods. The other five were only 15 m up the slope from the woods. The rocks at the bottom of the slope where the voles were caught were partially covered with, or embedded in, soil. These results contradict Stormer (1968) who stated that 'the occurrence of P. leucopus is inversely related to talus rock; while the occurrence of C. gapperi is positively related to talus rock.' Since the talus slope was the only area trapped in this study, it is impossible to say how the rodent population in the rocks compared with that in the surrounding woodland. However, comparisons can be made with population estimates of rodents made on both wooded and old field sites in areas less than 30 km away from the den area (Spring, 1977). Two forested areas which ranged in size from 1.4 to 1-9 ha were trapped in the spring of 1977. Spring caught mainly P. leucopus and only a few Microtus. The average population estimate of P. leucopus for these two areas was 12/ha. If this estimate is multiplied by the average body weight, there were about 394g of white-footed mice per ha. The two old field sites contained almost exclusively M. pennsylvanicus, with very few Peromyscus being captured. The average population estimate was 51 Microtus/ha. If this estimate is multiplied by the average weight of all Microtus captured, the old field averaged 1597 g/ha. In comparison with Spring's trapping areas, it appears that B den has a higher small rodent biomass. Using the average Peromyscus weights obtained from Spring's data, and the average Clethrionomys weights from Burt and Grossenheider (1964) with the population estimates of the Schnabel estimator, the den trap grid was estimated to contain 1007 g of mice and 639 g of voles. No timber rattlesnakes were dissected for food items in this study. In other studies, Peromyscus, Clethrionomys, and Microtus made up more than half the food items found (Barbour, 1950; Bush, 1959; Keenlyne, 1972; Savage, 1967; Smyth, 1949; Uhler et al., 1939). Thus there was considerable potential food available to snakes at the den and it can be deduced that the released snakes which left the den area probably did so for reasons other than food availability.

Snakes released at new den sites The release experiments were carried out at B den where a total of 33 rattlesnakes were released in 1976 between 23 June and 25 September (Table 1). Six of the 33 snakes were subsequently recaptured at B den. Three were recaptured in autumn 1976, but were not found in either the spring or summer of 1977. Two others were found in the spring, but not in the autumn, and one snake was captured in both autumn and spring. In autumn 1976 there were not many days conducive to snake hunting. Cold weather came early, and days warm enough for snakes to be out sunning were few. However, the den was checked almost daily in the spring, and on the days it was hunted, it was the usual routine to walk around it at least twice.

26

JOHN H. GALLIGAN, WILLIAMA. DUNSON

The total number of snakes captured at B den in spring 1977 was the lowest in three years, yet it was checked more often than in either of the two previous years. M a n y hunters at various snake hunts in the state had similar complaints. Some snakes might have been killed in the unusually cold winter of 1976-77. The frost line in State College that winter went deeper than 1.4 m, which was 0-6 m deeper than normal. Another possible explanation for the scarcity of snakes is that the rapid spring warming caused the snakes to leave the dens earlier than usual. The effect that winter weather may have had on the number of released snakes recaptured is impossible to evaluate. However, there is reason to believe that m a n y of the snakes left the area immediately after release. On 23 June, 1976, 20 snakes were released one at a time, a procedure which took about 20 minutes. By the time that last snake was released, a few snakes were observed to be already 30 m away. Five of the snakes released at another time in 1976 were followed for a limited distance by sight, the results of which are discussed below. TABLE

1

R E C A P T U R E OF A D U L T SNAKES T A K E N FROM T H E Q U E H A N N A W I L D AREA A N D T R A N S P L A N T E D T O B D E N O N B A L D EAGLE R I D G E

Number of snakes released Males

Females

13

7

Date of release

23 June 1976

Number of snakes recaptured

1 1

Totals

5

0

3 2 1

0 0 2

24

9

6 July 1976 13 July 1976 14 July 1976 25 September 1976

1 1 1 1

Date of recaptures

9 September 1976 16 May 1977 4 October 1976, 12 October 1976, 30 April 1977 9 September 1976 5 May 1977 4 October 1976

6

Release and recovery o f newborn rattlesnakes

tn 1976, a total of 48 newborn rattlesnakes were.released at den B in the following sequence: eight on 23 August, six on 25 August, eight on 27 August, 22 (3 litters) on 29 August, and four on 15 September. All but the last four, which were retained nine days due to cold weather, were released within 48 h of their birth. The young may undergo a process of imprinting to a specific site, and it was hoped that release at such an early age would permit the process to proceed naturally. Each of the first three litters was released together in different locations. The group of 22 newborn snakes was distributed singly around the den so as not to overpopulate any one location and make it unnaturally hard for them to find food. The young snakes were observed to move very little for about the first seven days, and then to disperse slowly. The only means of identifying a snake was through scale clippings on the ventral sides of its tail, which meant it could only be identified by handling. N o

BIOLOGY AND STATUS OF TIMBER RATTLESNAKE POPULATIONS

27

newborn snakes were captured for the five weeks following the first litter's release since the snakes moved very little at first and it was hoped to keep all disturbances to a minimum. After five weeks the weather quickly turned cold, and there was only one good day to hunt snakes. On that day (12 October, 1976), three marked and two unmarked baby rattlesnakes were captured. The three marked ones had all been released on 29 August, 1976. The two unmarked young were probably both from the same mother, as only one gravid rattlesnake had been found at the den. The next spring and summer (1977) an intense search of the den produced one young rattlesnake. It was a marked one that had not been captured since its release on 29 August, 1976. It appeared to be in good condition and had increased in snoutvent length from 24.0 to 27-8cm. Its weight had increased slightly from 17.4 to 17-6g. Although it is to be expected that not all snakes at a den will be found by someone searching for them, the capture of only one young rattlesnake in 1977 out of 48 released there in 1976 suggests either a large mortality or emigration from the area. Mortality could be caused by several factors, such as predation, starvation or freezing. Although no work has been done on mortality in timber rattlesnakes, some conclusions can be drawn from studies on other species. The results of a study spanning 10 years on the Pacific rattlesnake (Crotalus viridis oreganus) showed that there was a very high mortality among the newborn young (Fitch, 1949). The largest decline was felt to have taken place between birth in the autumn and the following spring. Fitch estimated that the population doubled every autumn due to the presence of young, yet by the next spring and summer the newborn snakes made up only 22-5 ~ of the population. This figure declined even further to 9.4 ~o by the second year. Fitch and Twining (1946) reported that they found many emaciated young and believed that a lot of young Pacific rattlesnakes died due to insufficient food. Wright (1941) felt that an apparent high mortality among young massasaugas (Sistrurus c. catenatus) was due to their inability to find food which they could swallow and perhaps also because young snakes may not have hibernated deeply enough to get below the frost line. Klauber (1956), in studies comparing the weight of prairie rattlesnakes (C. v. viridis) before and after hibernation, concluded that the adults lost 4 ~ of their weight during hibernation, and juveniles about 20 ~. Hirth (1966a), in a study on Great Basin rattlesnakes (C. v. lutosus), found that newborn snakes lost an average of 25.5 ~o of their body weight during hibernation compared with 8-8 ~ and 6-3 ~ body weight lost by adult females and males respectively. Predation is probably also a major cause of mortality. Fitch and Glading (1947) and Fitch (1949) suggested that predation accounted for the loss of a large number of newborn Pacific rattlesnakes (C. v. oreganus). They found remains of rattlesnakes in feces of coyote and fox and in the pellets of red-tailed hawks and horned owls. They also suspected cooper and sparrow hawks and striped skunks of feeding on young rattlesnakes. Klauber (1956) pointed out that not only does a malnourished young snake face the dangers of starvation, but also increased

28

JOHN H. GALLIGAN, WILLIAM A. DUNSON

predation since it must spend more time exposed searching for food. In the present study red-tailed hawks and a fox have been seen in the den area near where the newborn timber rattlesnakes were released. Fitch (1949) reported that emigration may also be common among young snakes. He found that 95 ~ of the snakes caught in an area that had been heavily hunted for a long time were yearlings, as opposed to 22.5 ~o in undisturbed areas. Such a high emigration rate might serve to expose the newborn snakes to increased predation and lessen the chances that a suitable place for hibernation would be found. It is uncertain whether rattlesnakes in Pennsylvania are born at the den and remain to hibernate there. Swanson (1952) believed that young timber rattlesnakes in Pennsylvania were born at such a distance from the den that they were forced to hibernate away from it. He claimed he had never found an immature snake at a den. Steven Harwig (personal communication), one of the most knowledgeable persons on timber rattlesnakes in Pennsylvania, also believes that the young are not usually born at the den entrance. He stated that gravid rattlesnakes congregate at a 'maternity rock', which may be the spot closest to the den that is a good location for sunning and also offers a retreat from heat and predators. Similar aggregations of gravid females have also been described for other snake species (Fitch, 1960; Fitch and Shirer, 1971 ; Klauber, 1956; Noble and Clausen, 1936; Tinkle, 1957, Viitanen, 1967, Wharton, 1966). During the course of this study, a few young rattlesnakes were found at dens. The finding of two newborns at den B in the autumn was described earlier. At a den in Huntingdon County, rattlesnakes measuring 26.4, 28.9, 37.8 and 43.8 cm in total length were captured in the spring. The two smallest ones had only buttons on their rattles and the other two had only a button and one segment. The two smallest, and perhaps all four of them, had probably been born the previous autumn at or near the den. N o r m Erickson, a commercial hunter who sometimes butchered rattlesnakes for meat, claims that 90 to 95 ~ of the snakes he has caught at dens in July and August were gravid, suggesting that the young would have been born at a den. At least three studies have reported an absence of appreciable numbers of immature rattlesnakes at dens (Hirth, 1966a; Heyrend and Call, 1951; Woodbury and Hansen, 1950). One of these (Woodbury and Hansen, 1950) acknowledged that young may at least occasionally be born at the den, while the other two reported the discovery of some newborn rattlesnakes which had 'arrived at the den'. Hirth (1966b) reported that young had 'arrived at the den after the last juvenile and adult had entered'. The fact that newborn snakes were still arriving at the den after the older snakes had entered supports the belief that many of the youngest age class may die from freezing due to not finding a suitable place to hibernate before the cold weather arrives. Tracking o f snakes released at a novel location Five snakes released in a new location (den B) and tracked by sight moved in the same general direction, at an azimuth of 60 ° (Fig. 5A), along the ridge. The snakes

BIOLOGY AND STATUS OF TIMBER RATTLESNAKE POPULATIONS

29

N

J A

B 7

4,

C

0

5

E

250

F

500

750

IO00m

Fig. 5. Movements of non-native rattlesnakes released at B den. The triangular points represent the location similarly marked on the topographic map of the den in Fig. 3. Numbers represent the successive points of observation, except in A where they mark the position of five snakes tracked to final distances of 18, 75, 96, 108 and 220m. A. Sight tracking of five snakes released in 1976. Note the similarity of directional headings along the ridge top. B. Radiotracking of an adult male released in 1977. C. Radiotracking of an adult male released in 1977. D. Radiotracking ofa gravid female released in 1977. E. Radiotracking of a gravid female released in 1977. F. Radiotracking of an adult male first released in 1976, then recaptured and tracked after emergence from hibernation at B den.

30

JOHN H. GALLIGAN, WILLIAM A. DUNS~)N

N 5

5

0 /

~-I

,--,

4

250

500

750

I000

I

I

I

I

m

D Fig. ~-contd.

first moved uphill from their release point and then followed the crest of the ridge. Individual snakes were followed for 18 to 220m. Three of the four rattlesnakes which were force-fed transmitters and released at den B showed very similar movements (Fig. 5B, D, E), The two males which overwintered in the lab were released together at 1100 on 4 June, 1977. One male (Fig. 5B) travelled along the ridge for 263 m and then took refuge in rocks at the top of the talus slope 9 h later (point 2). The regurgitated transmitter was discovered five days later at a point 524 m f r o m the snake's last known location (point 3). The second rattlesnake was tracked a distance of 67 m over seven days (Fig. 5C). By evening of the first day of its release, it had only moved 51 m (point 2). Several days

BIOLOGY AND STATUS OF TIMBER RATTLESNAKE POPULATIONS

31

later the regurgitated transmitter was found just a few ,metreslaway from its last , retreat (point 3). A gravid female rattlesnake was released at 1330 on 13 June, at the same release point as the two males just discussed. Its direction of travel was rather straight, paralleling the direction of the ridge for about 1170 m (Fig. 5D). On 27 June, this rattlesnake was again released at a point 9 m WSW from its previous site. This time, however, the snake was brought into the den from a southwesterly direction, instead of a northeasterly one. It was carried to the release point in the same way as before. The snake was released at 1100 and recaptured at 1300. It travelled in the same general direction as previously, and was recaptured at a point on top of the ridge 15 m N E from its release point. A second gravid female was released at 1255 on 16 July at the same location as the preceding female and it followed a similar course (Fig. 5E). During a 25 h period, it travelled at least 614 m.

Telemetry of snakes on emergence from hibernation The movements of two rattlesnakes which were captured at den B in the spring of 1977 were monitored by telemetry. Both rattlesnakes had been released at the den the previous summer and had apparently overwintered there. The first snake (Fig. 5F) was recaptured on 5 May, held in captivity for about 2 h, and then released with a transmitter. It moved from the ridge down a talus slope to a point only 2 m from the woodland edge. On 11 June, the snake was still at the same spot and had not been located elsewhere during the previous 14-day interval. The snake then began to move along an arc through woodland and then onto talus rock where it was observed trying to shed its old skin, which had broken into pieces. The following morning, the snake was located for the last time beneath rock 15 m up the talus slope. The second rattlesnake (Fig. 6) was captured at the den in a talus slope on 30 April. It was force-fed a transmitter, and released where it was caught within 2 h of its capture. The snake stayed at this same location for seven days. It was then lost and could not be located until 11 May when it was found by sight 27 m SW (along the slope) of its release point (point 1 on Fig. 6). As the snake's transmitter was not being received, the snake was captured and given a new radio. It then moved from this location SSW down the slope 23 m. The snake stayed at this spot (point 2) for three days until it moved 3 m SW to a new site (point 3) for another three days. From this location, the snake then went 22 m N W to a spot just over the crest of the ridge (point 4). The rattlesnake then stayed at this location from 5 May until 2 June. On 3 June, it was discovered 7 m SW from its last location (point 5). The snake had obviously shed since its last sighting two days before, and some searching at the area produced its old shed skin, tangled in briars and readily identifiable through scale clippings. Using the location of this shed skin as a new point, it was discovered that the snake had not just travelled 7 m SW, but had gone at least 8 m SE and then 9 m NW. F r o m 3 June until 13 June, this rattlesnake was never seen more than 0.5 m away from a ledge it used for sunning. Then, on 14 June, the snake was found 41 m away at a

JOHN H. GALLIGAN, WILLIAM A. DUNSON

32

N

II

12

18 0

Fig. 6.

I00

200

300

400

500m

Radiotracking of an adult male rattlesnake in 1977 after emergence from hibernation at B den This was a non-native snake first released in 1976.

BIOLOGY AND STATUS OF TIMBER RATTLESNAKE POPULATIONS

33

location which was 10.5 m into the woods at the SW bottom of the den (point 6). For the next ten days, the snake was in a new location every time it was found. During this period, it was tracked for 762 m and had travelled across a ravine and then along the top of the next ridge. The first part of its movements (from point 6 to point 12) was in a southerly direction. Once the snake came to the top of the ridge, however, it turned south-westerly and followed the crest. On 26 June the snake was found (point 17) only 7 m away from its previous location (point 16) two days before, and was captured in order to give it a new transmitter. It had eaten, and a partially digested chipmunk had to be forced up to get the transmitter which lay behind it. After replacing the transmitter, the chipmunk was also force-fed to the snake. The snake was located five days later at the same location, and no regurgitated chipmunk could be found in the area. Seven days later on 8 July, the snake was found 154 m further to the SW along the top of the ridge (point 18). This was the last time it was found. During the 69 days that this snake was followed, it had travelled 1055 m, with most of the distance (803 m) being covered in 11 days. Some factors affecting movements Although it is not clear if the two introduced snakes caught at den B in the spring had become permanent den residents, they showed a different type of movement than that observed with those snakes which had recently been released at the den. Both rattlesnakes which had hibernated at the den moved very little until the second and third weeks of June. Why these snakes stayed so long in the den area, and then apparently left it so quickly, is difficult to explain. The snakes may have been waiting for the right time of the year to go to summer ranges. They may have also been affected by their shedding condition as neither left the area before shedding. One left 12 days after, and the other apparently immediately after shedding. Some snake hunters claim that the snakes will not leave the den before shedding, although this has not been reported in any scientific studies. Movement of one of the rattlesnakes could also have been induced by handling. This snake always moved to a new location on the talus slope immediately after being handled. After being handled for the last time, it travelled more rapidly than usual for five days, before it was lost. There was also a difference in the speed and direction in which the newly released and 'resident' snakes moved. The movement of newly released snakes was immediate, rapid, and unidirectional along the ridge in contrast to the movements of the snakes which had hibernated at the den. Even when one rattlesnake which had overwintered at the den was moving away from the den, it moved much more slowly than the newly released snakes. This rattlesnake also moved away from the den in the opposite direction to that travelled by the newly released snakes. These results are in agreement with a study done by Landreth (1973) on Crotalus atrox. He found that 'snakes in foreign environments moved on fairly straight courses and for greater distances each day than native animals'. Fitch and Shirer (1971) also found that displaced C. h. horridus moved much more than those left at their original sites of capture.

34

JOHN H. GALLIGAN, WILLIAM A. DUNSON

Many studies (Brown and Parker, 1976; Fitch and Shirer, 1971; Fraker, 1970; Hirth, 1966b; Landreth, 1973; Noble and Clausen, 1936; Seibert and Hagen, 1947) have found evidence of homing ability in a total of ten different snake species. Fitch and Shirer (1971) were the only ones to work with timber rattlesnakes; they studied three individuals. Two of these rattlesnakes were displaced before tracking. One snake, a gravid female, was displaced a few kilometres and followed for eight days until lost. During this time, it travelled a total of 942 m with a distance of 421 m being covered on the seventh day. The snake also 'remained on or near the hilltop outcrop, following the rocks in a direction which did not bring it appreciably nearer to the location of original capture'. This was in contrast to the travels of a timber rattlesnake (not displaced) which was followed for more than 27 days, during which time it was never more than 105 m away from its original capture point. Another timber rattlesnake was displaced 229 m and returned to its original capture point by an indirect route two weeks later. In our 1976 studies snakes were transported to their release sites in light coloured snake bags. Landreth (1973) showed that the western diamondback rattlesnake (Crotalus atrox) when moved in view of the sun would often crawl in the direction in which they were translocated. Thus, there was the possibility that the snakes were just retracing the path taken to the release point. The snakes we released in 1977 were carried to their release point in snake bags enclosed in a red nylon backpack and a 'control release' was made. When a rattlesnake that had previously been followed 1172m (Fig. 5D) was released again at the den after being carried in from the opposite direction, it travelled in the same direction as before.

Size distribution There were few small timber rattlesnakes in the sample available for this study. Of 221 snakes measured, only 32 had snout-vent lengths (SVL) less than 600mm. Similar differences in the number of small versus large snakes have been reported for timber rattlesnakes (Langlois, 1964) and other rattlesnake species (Hirth, 1966a; Heyrend and Call, 1951 ; Woodbury and Hansen, 1950). In timber rattlesnakes, this absence of small snakes could be partially a result of high mortality in the young as discussed previously, and of a long life expectancy once adulthood is reached (Klauber, 1956; Perkins, 1950, 1955; Say, 1819; Shaw, 1957, 1962). However, the effect is probably exaggerated by differences in the behaviour of snakes of different sizes which result in a greater capture of older snakes. Male timber rattlesnakes attain a larger size than females (Fig. 7). No snakes smaller than 450 mm were included. Only 10 ~ of the female, but 42 ~ of the male, rattlesnakes measured had a SVL of 900 mm or greater. Furthermore 21 ~ of the females had a SVL of less than 700 mm, whereas this group included only 7 ~o of the males. The larger size in males may be the result of a slower growth rate in females after they reach maturity, a longer lifespan in males, or both. Gibbons (1972) suggested that females are smaller because no reproductive advantage is gained by

35

BIOLOGY A N D STATUS OF TIMBER RATTLESNAKE POPULATIONS 25

×

io

I-

hi

•

o'° I..,.

L

m

H

~.~

FEMALES

<~ .J I.LJ

is

IO

6

_N l~

~

5

o

2

2.

500

3

600

9 6

5

4

700

800

SVL, Fig. 7.

is

900

I000

I100

MM

Histogram of snout-vent length (SVL) of male and female rattlesnakes. Numbers on the top of each column are sample sizes. Measurements are in mm.

snakes of a larger body size. This seems doubtful in the light of some studies which have found that larger snakes generally produce more young per litter (Tinkle, 1957, 1960, 1962). There may be a selection for larger male body size in association with male combat dances (Sutherland, 1958; Gibbons, 1972). Sex ratio A total of 173 rattlesnakes were sexed after excluding the snakes obtained at the Morris snake hunt because they did not constitute a random sample. This number also does not include some small rattlesnakes which were not sexed. Of the 173 snakes, 111 were males and 62 were females, resulting in a ratio of almost two to one. This may just reflect a difference in the behaviour of the sexes which results in one sex being caught more readily. At the Morris snake hunt, a group of selected large snakes was sexed and half of the 66 snakes examined were females. Skewed sex ratios in favour of males in rattlesnake populations have been noted before (Fitch, 1949; Julian, 1951; Klauber, 1956; Woodbury and Hansen, 1950). Two litters of newborn rattlesnakes were sexed in this study in 1977, and 9 out of 14 young were found to be males. However, Klauber discovered that both sexes were evenly represented in an examination of 1491 young of the year. He believed that there was an excess of adult males of only about 10 ~ due to a slightly higher mortality among the females. However, owing to differences in activity between the sexes, more males were usually captured by snake hunters, leading to an 'apparent' excess of males. This idea is supported by Fitch and Glading (1947), who found that gravid female Pacific rattlesnakes (C. v. oreganus) were less active than males from July to October. Fitch and Twining (1946) reported a decline in the number of female Pacific rattlesnakes captured, but also that during the season when females

36

JOHN H. GALLIGAN, WILLIAM A. DUNSON

were active the sex ratio still ran almost two to one in favour of males. Furthermore, gravid females may aggregate near the den, leading to a greater likelihood of capture by hunters. In the only long-term study of sex ratios in a rattlesnake population, Julian (1951) reported that female great basin rattlesnakes (C. v. lutosus) 'dropped out' of the population sooner, indicating that males are longer lived. Julian found that the sex ratio changed from one to one at birth to about two to one in favour of males by the age of 7-8 years.

Size of females at sexual maturity Female timber rattlesnakes in Pennsylvania are already sexually mature when they reach a SVL of 770 mm and attain a body weight of about 430 g, as determined by the size of the smallest rattlesnake known to produce a litter. The actual size at onset of sexual maturity is probably less than this as a gravid female of this size would presumably have become mature in the preceding autumn. Klauber (1956) reported that his smallest gravid timber rattlesnake was 887 mm in total length. He does not cite the locality of this specimen. Five of the females which produced litters in our study and nine out of 14 females found to be gravid in 1976 were smaller than Klauber's reported minimum size. In 1977 one of the two gravid females captured to be used in telemetry experiments was also under 887 mm. The average total length of 16 gravid females was 876mm while the smallest gravid female had a total length of 819mm (68mm smaller than Klauber's reported minimum). The largest pregnant female had a total length of 952 ram. Gibbons (1972) found that female canebrake rattlesnakes (C. h. atricaudatus), a southern subspecies of the timber rattlesnake, exceeded 1000mm in SVL and weighed over 700 g at sexual maturity. Although both timber rattlesnakes and canebreak rattlesnakes reach similar maximum sizes (1880mm), the timber rattlesnake's average size (910-1370mm) is about 160mm less than that of the canebrake's (1070-1520 mm) (Conant, 1975). These differences most likely do not mean that timber rattlesnakes breed sooner in Pennsylvania than elsewhere, but probably reflect instead the short growing season for snakes in Pennsylvania.

Female reproductive cycle Between 16 June and 18 August, 1976, 37 female timber rattlesnakes with an SVL greater than 770 mm were palpated, and 14 were determined to be gravid. An SVL of 770 mm was chosen as the size of known sexual maturity because it was the size of the smallest female timber rattlesnake to produce young in the laboratory. Since only 38 ~ of the females examined were gravid, a cycle of at least two years seems likely. It is possible but less likely that the small number of gravid females is the result of different behaviours in gravid and non-gravid rattlesnakes, which results in a disproportionate number of each type being captured. Much information now exists to support the belief that viperids which range into

BIOLOGY AND STATUS OF TIMBER RATTLESNAKE POPULATIONS

37

northerly climates have a biennial cycle, especially near the northern limit of their distribution (Burkett, 1966; Fitch, 1949, 1960; Gibbons, 1972; Glissmeyer, 1951; Klauber, 1956; Rahn, 1942; Wharton, 1966; Woodbury, 1951; Woodbury and Hansen, 1950; Viitanen, 1967). The reason usually suggested for this is the limited active season of snakes in northern regions which prohibits them from obtaining the amount of food necessary to meet the energy demands of an annual cycle, and/or does not allow enough time for the embryo to fully develop. Tinkle (1962) proposed that follicular enlargement and fat storage must take place before hibernation if a snake with a biennial cycle is to reproduce the following season. Fat body size has indeed been shown to be related to the reproductive state of the female (Gibbons, 1972; Tinkle, 1962; Wharton, 1966). Some authors (McCoy, 1975; Petersen, 1970) have concluded from an analysis of other snakes that the timber rattlesnake also has a biennial reproduction cycle. The small percentage of gravid females could also be interpreted to mean that at least some of the females have a longer than biennial cycle. The length of the reproductive cycle may lengthen due to a decrease in the growing season as a snake reaches its northern limits. St Girons (1957) studied Vipera aspis on the Brittany peninsula in France and discovered one, two and three year cycles within a distance of 160 km. The percentage of gravid females in his biennial area was 54 ~ and in the triennial region 35 ~o. Whether a female will be able to reproduce within two years of a previous litter may be determined by whether or not a minimum of fat reserves have been built up. St Girons found no V. aspis females with mature eggs in the spring if they had less than a certain minimum amount of fat. Gibbons (1972) felt that the season may not be long enough for C. h. atricaudatus to build up enough fat to be on a biennial cycle in South Carolina. Wharton (1966) found that cottonmouths of Cedar Keys, Florida, have a biennial cycle which is not influenced by the length of the active season of the snakes as much as by the limited food supply found on the islands. Perhaps every two years is as often as a timber rattlesnake can reproduce in Pennsylvania, the deciding factor being just how successful a female is in obtaining food.

Growth rate A very rough indication of growth rate can be obtained by plotting the relationship between SVL of snakes measured, and the date of capture (Fig. 8). Unfortunately the majority of the 182 snakes plotted were measured during a one month period, and only the first few age classes are distinguishable by visual inspection. The young were born in late summer and early autumn with a SVL of 220-280 mm. Snakes between 400 and 550 mm are probably in their third summer. However the data are difficult to interpret without an accurate means of determining age. In their fourth summer, the snakes may have reached a SVL of 640-740 mm. In the fifth summer, the snakes may be 760 to 900 mm. If the SVL of the smallest female

38

J O H N H . G A L L I G A N , W I L L I A M A. D U N S O N

1200

0

o 1000

@

o

80

o O

80

8 |o 0 o

800

|. IV!

b

~E ~E ®

g

o

> or} 0

600 o- MALE •- FEMALE " " UNSEXED

• o

400

LI

A

A AA

20C

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A

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i

i

,

M d J A MONTH OF THE YEAR

i

S

Fig. 8. The snout-vent length (SVL) of rattlesnakes captured during April (A) through September (S) of 1976. The arrow indicates SVL of the smallest gravid female found. Measurements are in mm.

39

BIOLOGY AND STATUS OF TIMBER RATTLESNAKE POPULATIONS

to produce young is used as an index of sexual maturity, some females may attain maturity in their fifth or sixth summer and produce their first litters in their sixth or seventh summer. Once sexual maturity is reached, the growth rate undoubtedly slows down. This slowdown m a y be partially due to the buildup of fat bodies in years when they are not reproducing (Tinkle, 1962), and the reduction in the amount of food eaten during years when they are reproducing (Keenlyne, 1972). Gibbons (1972) examined the ovaries of the canebrake rattlesnake in South Carolina and concluded that females did not have their first litter until six years after birth. However in re-examining his data it Seems that females could produce litters at the end of their sixth summer at an age of five years. Therefore, female timber rattlesnakes in Pennsylvania may mature at approximately the same age as the southern subspecies but at a smaller size. Litter size Seven female timber rattlesnakes held in the laboratory gave birth to young in 1976 and two gave birth in 1977 (Table 2). The mean litter size was seven young and one TABLE 2 INFORMATIONON LITTERSOF TIMBER RATTLESNAKESBORN IN THE LABORATORY

Snake number

B-24 B-32 E-87 B-15 B-43, B-49, E-86 c B-80 B-83 Mean

Number Total Number of Snout-cent Female body weight, g of w e i g h t undereloped l e n g t h , BeJbre After young of young, eggs mm birth birth g 8 6 5a 8

138-4 178.8 99.8 177.6

1 1 3 1

22

374.0

2

9 5

196.6 102.9

7

140-9

Weightlost by female as % initial body weight

0 1

775 811 874 b 810 901 770 855 819

538-0 580.5 631.7 582.8 413.7 592.5 430-0 529-3 464-3

301.0 315-0 440.0 308-0 217.5 421.0 205.2 301.7 314.2

44 46 30 47 47 29 52 43 32

1

827

529.2

313.7

41

Includes 1 young born deformed which died shortly after birth. b No snout-vent length measurement was taken but since it had a total length of 838 mm its snout-vent length would probably have been less than 792 mm. c Data from three females were pooled (see text for explanation).

undeveloped egg. The range of the litter sizes is not clear because three females in the same cage all had their litters the same night. The largest litter recorded was nine young and no undeveloped eggs. One of the largest females (SVL 875 mm) had a small litter of five, while the two smallest females (SVL 775 m m and 792 mm) each had litters of eight young and one egg. No conclusion about the relationship between a female's size and its litter size should be drawn from such a small sample size. Gibbons (i 972) found no relationship between length of the female and litter

40

JOHN H. GALLIGAN, WILLIAM A. DUNSON

size in the canebrake rattlesnake, but he too had obtained his results from a small sample size of 16. In C. atrox larger females do have larger litters (Tinkle, 1957, 1960). The weight loss due to parturition of the females in this study varied between 29 and 50 % of the body weight. Six of the nine females lost from 43 to 52 %, and the others lost, 29, 30 and 31%. The snakes which lost 30 and 32 % had the smallest recorded litters of five young. Although the relative weight losses of females after giving birth were often similar, length and weight of individual newborn snakes showed much variation. For example, two similarly sized females which weighed 581 and 583 g lost 46 and 47 % in weight after parturition. The female which lost 46 % had six young and one undeveloped egg. The other female gave birth to eight young and one undeveloped egg. Newborns from the female with fewer young were 34 % heavier and 34 % longer than those of the female with a larger brood. The total weight of the six young from the smaller brood was 178.6 g while those of the larger litter of eight totalled 177.8 g, a difference of only 0.8 g. The average litter size of seven young observed for the nine females in this study is less than has been reported elsewhere. Klauber (1956) reported the litter size of C. h. horridus to range from five to 17 with a mean of 10. However, some of his data were obtained by dissecting females and counting enlarged eggs. This may have resulted in a higher than normal count since undeveloped enlarged eggs were present in almost all litters observed in this study. Gibbons (1972) determined (through dissection) the litter size of 16 female C. h. atricaudatus in South Caroline to range from l0 to 16 with a mean of 12.6. Time of birth The dates of the seven births observed in this study in 1976 ranged from 22 August to 14 September. Three females brought into the laboratory on 18 June had litters on 22, 24, and 26 August. The other females brought in on 2 and 12 July, and 12 August all had young on 28 August. The female which gave birth 14 September was moved into the laboratory on 13 August. In 1977, two females brought into the laboratory on 12 June produced young on 12 and 17 August. Parturition dates of timber rattlesnakes previously reported range from 20 August to 8 October. E. M. Cheuvront of Aliquippa, Pennsylvania (Klauber, 1956), reported that 8 female timber rattlesnakes caught in early September gave birth to young on 15, 18, 21, 24, 25 and 26 September and 1 and 8 October. Ditmars (1936) reported birth dates to be 6, 7, 12 and 18 September. Other reported dates are 13 and 15 September (Conant, 1938), 8 September (Trapido, 1939), 26 August (Edgren, 1948) and 20, 24 and 26 August (Petersen, 1970). Since rattlesnakes are poikilotherms any temperature changes in the environment will have an effect on the duration of gestation. Blanchard and Blanchard (1940) reported that a 0.6C difference in a season's temperature during gestation caused a

BIOLOGY AND STATUS OF TIMBER RATTLESNAKE POPULATIONS

41

difference of 4.5 days in the date of parturition in Thamnophis s. sirtalis. A shortening in gestation time is therefore possible in captive snakes which are usually kept at a higher temperature than they would encounter in the wild. However, since the snakes brought into the laboratory 41 days apart in 1976 both had their young on the same day, while two snakes brought into the laboratory one day apart gave birth 17 days apart, the range of birth dates obtained may not have been greatly changed by the effects of captivity. Morphometric measurements Certain correlations were made between body weight, snout-vent length, head length and tail length in order to determine if any differences existed between the sexes or populations. It was also hoped that head length might be used as a predictor of snout-vent length, simplifying future field measurements. A correlation between snout-vent length and weight would also be useful in determining the general nutritional status of snakes. Snout-vent length (SVL) was directly correlated with head length (HL) (Fig. 9). Comparisons were made between the sexes and no significant difference was found. Comparisons of 24 snakes from the Clearfield County Fair showed a significant difference (P < 0.01) from all others. This difference is more likely due to the effects of captivity rather than genetic variation. When the snakes were obtained, it was noted that many appeared to be very underweight. The equation fitted to the individual points of all snakes (except those from the Clearfield County Fair) had a correlation coefficient (r) of 0-973. Although snakes of either sex with the same SVL have similar proportional head lengths, head length proportion does decrease slightly with increased size. Head lengths of newborn rattlesnakes are larger (6-38-7.40 ~o SVL; mean 6-89 ~o) than those of adults (3.51-6.25 ~ ; mean 4.42 ~o). Figure 10 shows the relationship between snout-vent length and weight. When plotted on a double logarithmic grid, the data described a linear function. Again, the only significant difference between groups or sexes was the group of snakes from the Clearfield County Fair (P < 0.01). If the snakes from Clearfield County Fair were excluded, the coefficient of correlation between SVL and W is 0.987. Kaufman and Gibbons (1975), in a study ofweight-SVL relationships of the canebrake rattlesnake found that the females were heavier than the males. Such a difference was not found in the present study. Kaufman and Gibbons examined 52 females and 54 males which had been collected over a 7-year period. The 109 males and 75 females (Clearfield County Fair snakes excluded) used in this comparison were almost all collected during 1976. Kaufman and Gibbons did not state how many of their females were gravid or if males and females were collected evenly during the season. If more females were collected closer to the end of the summer or autumn, a higher weight in females might be expected due to gravid snakes having nearly developed young and many non-gravid ones having a large store of fat in preparation for reproduction the following spring (Tinkle, 1962). Most of the snakes in this study

JOHN H. GALLIGAN, WILLIAM A. DUNSON

42 50-

•

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40

.

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. ",• ..=,..'.." "~" • •o e

°'

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•

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HL = 9.483 + 0.03289 SVL

I

10200 Fig. 9.

400

I

600 SVL,

I

800 MM

I

l

I000

1200

The relationship between snout-vent length (SVL) and head length (HL) in timber rattlesnakes (sexes combined).

had been measured by mid-July. Females which had given birth the previous autumn may not have had sufficient time to restore depleted fat bodies. Gravid females may not reach their maximum weight until nearer the end of the gestation period. Kaufman and Gibbons say that weight-SVL relationships did not significantly change due to season. In our study, the regression equation of the length-weight relationship in gravid females was compared with the regression equation for females known to be non-gravid. No significant difference was found. However, a difference may have gone undetected due to the small number of gravid females tested (N = 11). In Fig. 11 the relationship between relative tail length (expressed as ~o SVL) and ~VL is shown; there is sexual dimorphism. Male rattlesnakes had significantly greater tail lengths than females, but both showed considerable variation. Male tail

BIOLOGY AND STATUS OF TIMBER RATTLESNAKE POPULATIONS

5000

43

-

?. %°o

"i

500

o~°

'I,¢0 1 14,1 °

e

o

I00 w,.

50

SVL

-

• ~.5776W

0'~14

I

Q Q e

:t l IO I00

l

i

I

, , l,l

500

i

i

I

I000

SVL, Fig. 10. The relationship betweensnout-vent length (SVL) and body weight (W) in timber rattlesnakes (sexes combined). lengths were 5.3-12.3 % SVL (mean 8.1%); female tail lengths were 5.5-7.7 % (mean 6.5 %). The regression line for males is SVL = 235.4 + 8-82 T L and the coefficient of correlation (r) of this line is 0.86. The regression equation for females is SVL = 223-8 + 10.52TL, which has a coefficient of correlation (r) of 0.83. The mean total length of 62 newborn rattlesnakes was 265 m m and the mean weight was 20-4g. There was, however, much variation around these averages, mainly between litters (Table 3). The head length of the newborn snakes was 15.5-19.0 m m (mean 17.1). The head length was proportionately larger than it is in the adult. Stewart et al. (1960) took measurements of a litter of 12 newborn timber

JOHN H. GALLIGAN, WILLIAM A. DUNSON

44 II

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I 400

I 500

I 600

I 700

I 800

I , 900

I I000

1 I100

I 1200

S V L , MM

Fig. 11.

The relationship between snout-vent length (SVL) and tail length (TL) in the timber rattlesnake. Open circles represent males; closed circles represent females.

TABLE 3 BODY W E I G H T , HEAD L E N G T H S AND TOTAL L E N G T H S OF

Litter number B-24 B-32 E-87 B-15 B-43] B-49~ E-86J B-80 B-83

Number of young

Total length of young (ram) Range Mean

62

NEWBORN TIMBER RATTLESNAKES

Weightof young (g)

Head length (ram)

Range

Mean

Range

Mean

8 6 4" 8

225-273 279-308 276-286 272-283

256 294 281 276

16.1-19.4 27.2-31.8 23.2-23-8 20-2-23-9

17.3 29.8 23.4 22.2

16.0-18.0 17.0-19.0 16.0-18-5 16.7-17.5

17-0 18-0 17.5 17.3

22 b

245-278

257

13.4-20.0

17.0

15.5-18.0

16.6

9 5

261-277 259-279

287 274

19.7-23-6 19.9-21.2

21.8 20.6

16-3-18.0 17.0-17.5

17.4 17.4

° Malformed young not included. b Data from three females were pooled (see text for explanation).

BIOLOGY AND S T A T U S OF TIMBER RATTLESNAKE POPULATIONS

45

rattlesnakes one month after their birth. These snakes were generally longer and weighed less than the newborn snakes measured in this study. Total length was 289.9-330.0 mm (mean 303.7). Weight of the newborn snakes was 12.3-17.6 g (mean 15.2). Newborn snakes in this study measured within 24 h after birth, and with about the same mean body length of the one-month-olds studied by Stewart et al. (1960), weighed about 50 ~ more. The one-month-old snakes probably utilized some of that lost weight in growth, since the smallest snake measured by Stewart et al. was bigger than all but three of the 48 young snakes examined in this study.

Feeding rate in captivity Information on growth and feeding that is derived from captive snakes should not be applied directly to natural conditions. However it may be used, in the absence of field data, roughly to estimate the food intake of rattlesnakes. A juvenile male rattlesnake ate 738 g of white mice over a 199-day period (Fig. 12A). During this time, its weight increased from 257 to 388 g. If it is assumed that an average adult Peromyscus leucopus weighs about 25 g and a Clethrionomys gapperi averages 27g (Burt and Grossenheider, 1964), then the young male ate the field equivalent of about 30 adult Peromyscus or 27 Clethrionomys. The two females studied (Fig. 12B, C) started at the same weight (440 g), but 330 days after they had given birth, one was twice as heavy as the other. One snake (Fig. 12B) weighed 291 g after eating 440g of white mice, while the other (Fig. 12C) weighed 582 g after eating 1079 g during the same period. The first female had eaten the field equivalent of about 18 adult Peromyscus or 16 adult Clethrionomys in order to increase its weight by 34 ~ since parturition. The second consumed the equivalent of about 43 adult Peromyscus or 40 adult Clethrionomys during the same period and increased its weight by 184 ~ . Since the active season of wild rattlesnakes is about 150 days or less, and since outdoor temperatures are not as high as those in the laboratory, snakes similar in size to the mature females used in this study would probably eat less than half of the amount recorded here. Much will depend, of course, on how active a snake is, but nevertheless it appears that rapid growth requires a considerable number of rodents. In the rodent population survey an estimate of 45-Peromyscus was obtained for a 0.743 ha area at B den over a one week period. It would be necessary to monitor rodent population dynamics carefully over a season to determine the total production of rodents, and thereby the number of snakes that could be sustained. However, it appears very unlikely that any single area could permanently support a large number of rattlesnakes. Thus a summer migration away from the den may be obligatory for most of the hibernating rattlesnake population.

Interviews with commercial hunters Eleven commercial snake hunters, who have hunted a minimum of eight years each, were interviewed. Every one said that without a doubt there had been a great

46

JOHN H. GALLIGAN, WILLIAM A. DUNSON

180 160 140 120 I00 30 I-'10 LIJ ..J

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140 120 I00

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i 300

13°o 400

Fig. 12. Body weight gain in relation to the amount of food eaten in captivity by three timber rattlesnakes. The line with open symbols represents the body weight of the snake; the vertical lines represent the weight (as a percentage of the snake's initial weight) of food items. A. Juvenile male. B. Adult female which was gravid when its weight was first measured. The large drop in weight between day 45 and day 59 was mainly due to parturition. C. Adult female which was gravid when its weight was first measured. The large drop in weight between day 0 and day 17 was mainly due to parturition.

BIOLOGY AND STATUS OF TIMBER RATTLESNAKE POPULATIONS

47

decline in the number of rattlesnakes in the areas they hunted. Many felt that the largest decline had been within the last ten years. Most of these hunters stated that almost all of the big dens in their area had been hunted out and they were now hunting dens which they would not have bothered with ten years ago because the same dens were then considered too small. Another c o m m o n theme was how easy it was to 'hunt out' a den. Seven of the eleven hunters told stories about dens which had a large population of.snakes when first discovered. After five to seven years of hunting they were completely depleted. Summaries of parts of four individual interviews dealing with these points are presented below. N o r m Erickson is a district game protector in Emporium, Cameron County, who used to be quite an active commercial hunter. He has been hunting snakes for over 45 years, and although he no longer considers himself a commercial hunter, he was still selling 40-50 snakes per year in 1976. His experience as a commercial snake hunter, and the nature of his work as game protector, has given him the opportunity to become very familiar with an area considered by m a n y to be some of the best rattlesnake habitat in the state. He stated in an interview on 22 July, 1976 that there had been 'a very large decline in the number of rattlesnakes, especially in the last eight or nine years.' He claims he used to know of 35 to 38 good dens, but now knows of only one. Mervine Reed is a snake hunter from Milesburg, Centre County, who has been hunting for 17 years. He believes rattlesnake populations have declined, but thinks that the rattlesnake should be eradicated. He told of a den from which he took over 100 rattlesnakes and copperheads over a seven year period. In the last three years, he has not seen one snake there, even though he has been checking it frequently. Robert Mohney, a one-time commercial snake hunter with more than 30 years of experience in looking for rattlesnakes, hunts mainly in Clearfield and some of the surrounding counties. Prior to 1976, he said he could catch 13 to 15 snakes in one visit to one of his dens. In 1976, however, he was only able to catch a total of 11 after visiting 14 different dens. Ralph Fye is a commercial hunter from Karthaus, Clearfield County, with about 20 years of experience in finding rattlesnakes. Mr Fye hunts, a m o n g other places, the Quehanna Wild Area. He believes that the number of rattlesnakes is declining fast, and cited m a n y cases where snakes have been almost exterminated from good habitat. He said the only way he finds most of his snakes now is by using his fourwheel-drive jeep to get far away from any roads and by doing a lot of hiking. He claimed that when he started, he could catch more snakes along the roadsides than he can now with all of his hiking. He almost never sees a rattlesnake lying on the road now. As of 1976, he was still catching about 150 per year, but said that he was getting ready to quit because even though rattlesnakes are bringing more money, he feels too much work goes into catching each snake, now that they are getting so much harder to find.

48

JOHN H. GALLIGAN, WILLIAM A. DUNSON

Commercial uses

Rattlesnakes are sold to be eaten, skinned, mounted, displayed in roadside zoos and used in milking demonstrations, to be kept as pets, turned in for bounty, and to be used for their rattles and fangs. One use often mentioned but known to be false is in the preparation of antivenins. Dr M. Z. Bierly, Jr. (personal communication) of Wyeth Laboratories confirmed that the timber rattlesnake is never used in the preparation of polyvalent antivenin (Crotalidae). Rattlesnake hunts in Pennsylvania

There were seven organised rattlesnake hunts held in Pennsylvania in 1976. The purpose of a hunt is usually to enable hunters to compete for trophies in such categories as: most snakes caught, biggest rattlesnake caught, and/or others depending on the individual snake hunt. In order to compete one must first sign up at the hunt headquarters and pay a small registration fee. Captured snakes are then brought back to the hunt headquarters and turned into the wire 'pit' enclosure, where they are first counted and measured. At all of the hunts except one, all snakes entered are supposed to have been captured the day of the hunt. The hunt is usually sponsored by a group such as a fire company or sportsmen's club, which makes money at the hunt by selling food and drink to the hunters and tourists. At some of the hunts, money is also earned by selling memorabilia and running various games of chance. In 1976, Pennsylvania rattlesnake hunts were held as follows: Landisburg in Perry County (5-6 June), Morris in Tioga County (12-13 June), Clearfield in Clearfield County (19 June), Noxen in Wyoming County (19-20 June), Crossfork in Potter County (26-27 June), Lake City in Elk County (3-4 July), and Sinnamahoning in Cameron County (10-11 July). The organiser of the hunt may be an individual, a town organisation or a rattlesnake club. The Landisburg, Noxen, Crossfork, and Sinnamahoning hunts are run by the Keystone Reptile Club, while the Indiana County Reptile Association runs the Lake City hunt. The remaining two hunts are held by local residents. The hunts are usually good tourist attractions, and much of the people's time inside the 'pit' is occupied with holding snakes for photographs and answering spectators' questions. Since thousands of people attend these affairs every year, the manner in which the snakes are treated by pit officials, and the answers given to questions asked may have a very great effect on the spectators' attitudes towards the snakes. The Keystone Reptile Club held four rattlesnake hunts throughout the state in 1976. Data of the past Keystone Reptile Club hunts are presented in Table 4. The club (made up of 20-25 regular members) is a non-profit-making organisation, and it is the local sponsors such as a sportsmen's club or a fire company who make money through concession stands. All snakes captured at any of their hunts are released, but this does not, of course, mean that the snakes will survive. Two of the club activities which attract many spectators are free handling and sacking contests. Free handling is simply the picking up of a poisonous snake bare-handed. The club

BIOLOGY AND STATUS OF TIMBER RATTLESNAKE POPULATIONS

49

TABLE 4 STATISTICS ON

Hunt Landisburg Noxen

Crossfork

Sinnamahoning

PENNSYLVANIA RATTLESNAKE HUNTS SPONSORED BY THE KEYSTONE REPTILE CLUB

Date June 1975 June 1976 June 1977 August 1973 June 1974 June 1975 June 1976 June 1977 June 1973 June 1974 June 1975 June 1976 August 19694 July 1970 July 1971 July 1972 July 1973 July 1974 July 1975 July 1976 July 1977 July 1977b

Number of registered hunters

47 55 92 106

Number of rattlesnakes caught 15 35 26 6 22 96 54 47

18

45 69 202 225 209 291

37 17 46 51 63 71 62 40 26 19

Not run by the Keystone Reptile Club. bA second hunt was held by the Sinnamahoning Sportmen's Club on the same weekend as the one run by the Keystone Reptile Club in Sinnamahoning.

members inside the wire 'pit' enclosure spend a lot of time picking up rattlesnakes or copperheads while they are giving lectures about the snakes. Surprisingly enough, very few people are bitten while free handling; the club admits to only two rattlesnake bites in seven years. The sacking contests are a little more dangerous than the free handling, both to the contestant and to the snake. The objective of a sacking contest is to see how fast two people can put five rattlesnakes in a bag. A sacking team consists of a 'sacker' and a 'pinner'. The pinner must pin each of five rattlesnakes down with a snake hook, grab it behind the head, and put the snake into the bag which the sacker is holding opea. When the fifth snake is put into the bag, and the sacker twists the bag shut, the three timers stop their watches and average the times. Judges are supposed to watch the contest and if any snakes are hurt, a fivesecond penalty will be assessed. A sacking contest is held after each one of the Keystone Reptile Club's four hunts, and at the last hunt, in Sinnamahoning, a second sacking contest is held for the state championship. This latter contest includes those with the fastest times of the previous four contests. The Pennsylvania champion is then eligible to participate in the national championship held in Texas. The record time for a Keystone Reptile Club sacking contest is currently 18.2 s. It is not unusual for someone to be bitten, and to be awarded a patch that shows he is a member of the 'Sunken Fang Society'.

50

JOHN H. GALLIGAN, WILLIAM A. DUNSON

The Indiana County Reptile Association is a splinter group of the Keystone Reptile Club which broke offafter a dispute between a few of the members over some snakes being killed for skins instead of being released. The only real difference between the two organisations are some of the rules for the sacking contests. ICRA contestants are not permitted to pin the rattlesnake. They must instead pick up each of the five snakes barehanded and put them in a bag. The fastest 1976 time in sacking contests was 4.0 s. Due to the way the sacking contest is run, snake bites are not uncommon. The ICRA sponsored one hunt in 1976, which was held in Lake City (Elk County); 11 rattlesnakes were captured. The Morris hunt started in 1955 and is the oldest and largest snake hunt in Pennsylvania. It is run by the Morris Fire Company, but other organisations such as the local churches alsoset up stands. According to spokesman Ralph Miller, who also serves as a rattlesnake bounty agent for Tioga County, the hunt came into existence in 1955 to help make Morris a safer community. Morris runs the only snake hunt in the state which pays hunters for the snakes they turn in. Snakes need not have been captured the day of the hunt, nor in Tioga County, to be eligible for the contest. Most hunters freely admitted that they have been collecting snakes since the first warm days of spring, and usually at places far away from Morris. On the Sunday of the hunt, snakes are sold to the general public, at prices fixed according to size. All snakes not sold to the public are then sold to a snake dealer. In 1976, 87 were sold for $400 to a dealer in New York. In 1975, over 300 snakes were not sold, but died in their cages, while the town tried unsuccessfully to find a buyer. The hunt organisers were often heard telling tourists that the snakes go for medical research and in making of antivenin. Information on past snake hunts was difficult to obtain, and discrepancies often arose. For example, hunt officials, in defending the existence of their hunt, claimed that up until 1976, the usual number of rattlesnakes turned in at each hunt was about 400 snakes. The decline in 1976 was due to bad publicity, they said. When asked to see their records so that exact figures could be obtained on past years hunts, the officials said that no records were ever kept. However, figures on previous hunts were obtained from Diane Eaton, a reporter for the Wellsboro Gazette, who found them in articles written about the hunts in old newspapers. This information is presented in Table 5, and shows that 400 snakes was not the normal number turned in, but was the largest number of snakes ever caught. It is difficult to decipher any trends in the Morris snake hunt data. The number of registered hunters does not necessarily indicate how many people actually went hunting, or how long they hunted. A serious problem is that hunt officials do not want to release any figures which might be interpreted as showing a decline in the rattlesnake population. This has apparently resulted in an inflated report of the catch for 1977. Perhaps the only thing that can be said about the figures is that the number of rattlesnakes captured started to rise sharply in 1971, peaked in 1973 and then declined for three more years.

51

BIOLOGY AND STATUS OF TIMBER RATTLESNAKE POPULATIONS

TABLE5 CATCH STATISTICS FOR THE MORRIS SNAKE HUNT BETWEEN 1960 AND 1977

Date

Number of hunters

Number of snakes caught

Greatest number ofsnakes turned in by one hunter

1960 1961 1962 1963 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977

150 114 150 141 230 124 200 218 300 400 300 362 350 308 279 184 187

104 140

78 55 42 36 87 20 19 23 32 15 51 52 68 114 121 69 70

136 110 54 110 143 277 112 293 340 407 364 342 126 147~

° Actual catch reported by impartial observers was much lower, perhaps less than 80. R a t t l e s n a k e s at hunts often show signs o f physical a b u s e (Table 6). O b v i o u s e x t e r n a l s y m p t o m s included cuts, b r o k e n b o n e s a n d skin a b n o r m a l i t i e s associated with defective shedding. It is also likely t h a t even m o r e serious internal injuries n o t o b v i o u s externally are sustained b y the snakes d u r i n g c a p t u r e a n d handling. F o r e x a m p l e p i n n i n g a n d r o u g h t r e a t m e n t o f the snakes m a y cause vertebral injuries; m o u t h r o t m a y result f r o m m i l k i n g the snakes or forcing the jaws open. The snakes at the h u n t s are definitely m a l t r e a t e d a n d it is a m a t t e r o f s o m e d o u b t w h e t h e r m a n y o f t h e m can survive even if s u b s e q u e n t l y released in suitable h a b i t a t . TABLE 6 SOME OBSERVATIONS ON THE HEALTH OF TIMBER RATTLESNAKES TURNED IN AT PENNSYLVANIA HUNTS 1N 1976

Hunt

No. snakes examined

No. with skin shedding tears

No. with cuts or swellings

No. with broken bones

No. dead

67 37 41

14 11 2

6 4 8

1 1 1

2 0 0

Morris Crossfork Sinnamahoning

Rattlesnake bounties

B o u n t i e s have often been used as a n incentive for the d e s t r u c t i o n o f rattlesnakes. S o m e M a s s a c h u s e t t s towns h a d r a t t l e s n a k e b o u n t i e s as early as 1719 ( K l a u b e r , 1956). O t h e r states which have p a i d b o u n t i e s on t i m b e r r a t t l e s n a k e s s o m e t i m e in the p a s t include Iowa, M i n n e s o t a , V e r m o n t , N e w Y o r k , W i s c o n s i n a n d Pennsylvania.

52

JOHN H. GALLIGAN, WILLIAM A. DUNSON

Klauber (1956) states that rattlesnake bounties have been paid from time to time by sportsmen in the Pennsylvania counties of Cameron, Tioga and McKean. He also states that in 1951, a bill proposing a statewide bounty of $1.50 on poisonous snakes was defeated in the legislature. The only official bounty at present known to us in Pennsylvania is the one offered by Tioga county. The Tioga county bounty of $1-00 per rattlesnake was first paid in 1949 by the bankers of the town of Wellsboro. It was started in the hopes of making the county more attractive to tourists and settlers by reducing the number of rattlesnakes found there. In 1950, the responsibility for bounty payments was taken over by the county, which still pays it today. The $1.00 bounty can be collected by any Tioga county resident who turns part of a rattlesnake's tail and the rattle into a bounty agent. Data for most years of the number of rattlesnakes turned in under the Tioga County code are presented in Table 7. Such data are difficult to interpret since the number of hunters collecting, and the ages of the snakes are not known. A large drop or rise in the number of snakes turned in during a year might be attributed to the activities of just a few hunters. TABLE 7 NUMBER OF RATTLESNAKESTURNED IN UNDER TIOGA COUNTY'S BOUNTY BETWEEN 1949--54 ANO 1960-76

Year

No. of snakes

Year

No. of snakes

1949 1950 1951 1952 1953 1954 1960 1961 1962 1963 1964 1965

1500 1469 909 ll60 1525 1297 988 782 1558 1638 1334 1638

1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976

1334 1939 1258 1250 1529 647 1228 1575 1100 1100 389

PLAN FOR CONSERVATION

The most serious hinderance to proper protection of snakes is the shocking ignorance of their habits among the general public. Most residents of Morris interviewed felt that the rattlesnake was very dangerous, and that it was possible for a person to die from a rattlesnake bite before reaching a hospital for treatment. Many experienced snake hunters, on the other hand, felt that a rattlesnake bite would only rarely be fatal if no treatment was received. Unfortunately, data on snake bites are hard to obtain. Dr E. J. Witte of the State Health Department (personal communication) said that even though under the law all such bites must be reported

BIOLOGY AND STATUS OF TIMBER RATTLESNAKE POPULATIONS

53

to the Health Department, most hospitals never do so. He could say, however, that no one had died from snake bite in Pennsylvania in many years. During the period from 1943 to 1953 Pennsylvania sustained less than ten venomous animal fatalities in eleven years (Klauber, 1956). Since it is known that in the United States about 50 more people die every year from insect bites and stings than from rattlesnake bites (Anon., 1976), death from snake bite is thus very rare in Pennsylvania. Klauber also notes that only 3 ~o of all rattlesnake bites are fatal, and that most of the fatalities are caused by the eastern (C. adamanteus) and western diamondback rattlesnakes (C. atrox). Our own experience with the occurrence of snake bite is that almost all of the bites involve snake handlers, snake hunters, or people trying to kill the snake that eventually bit them. For example, all of the rattlesnake bites of which we have personal knowledge, six in 1976 and four in 1977, affected people catching or handling snakes. Current Pennsylvania regulations governing the catching or killing of rattlesnakes are scant. The only protective regulation is one which makes it illegal to damage a den while trying to catch snakes. The organisers of snake hunts are required to obtain a permit. This, however, only states that snakes are not to be caught by destroying a den and stipulates that hunt organisers must file a report stating how many snakes were caught and what was done with them. Organisers of a hunt may legally kill or sell the snakes if they wish. Rattlesnakes currently are killed legally in state or federal forests, state game lands and wild areas. We have heard many reports of foresters and employees of the fish and game commissions killing all rattlesnakes they find in the course of their duties. On 1 January, 1978, a new list of endangered, threatened, and indeterminate amphibians and reptiles became official. On this list the timber rattlesnake was classified as indeterminate (i.e. 'apparently threatened or uncommon to rare, but insufficient data available on which to base a reliable assessment of status'). No restrictions on commercial hunting or the killing of timber rattlesnakes by individuals or snake hunts are in effect. The eastern massasauga rattlesnake (Sistrurus c. catenatus) is listed as an endangered species on the Pennsylvania Fish Commission list. Due to the snake's restricted range in Pennsylvania (five counties), small size (51-76cm), and preference for swampy habitat it receives much less attention than the timber rattlesnake. This lower profile has made it much easier for it to achieve protection. In 1974 the Pennsylvania Fish Commission asked for and received the authority to protect all amphibians and reptiles in the state of Pennsylvania. In 1975 the Commission held a meeting, attended by many of the state's herpetologists, to discuss what actions needed to be taken in protecting Pennsylvania's amphibians and reptiles. One of the suggestions adopted by the scientists at the meeting was to require all rattlesnake hunts to release their snakes after the hunt. This proposal was short-lived however, after citizens of the town of Morris, Pennsylvania, asked State Representative Warren H. Spencer to intervene (Eaton, 1976). The people of Morris

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hold the largest snake hunt in the state and every year sell all the snakes they catch. Therefore, Representative Spencer stated his intention to meet with Fish Commission Director Ralph Abele 'to work out some type of arrangement so that the position they (the Commission) have taken will not hinder the village of Morr~ from continuing their snake hunt.' Following this, the Fish Commission drafted a 'permit' which did not include a provision requiring the release of any snakes. In February, 1977, a Herpetological Advisory Committee was convened and the status of Pennsylvania's amphibians and reptiles was again discussed. One of the results of the meeting was the setting up of a list of endangered, threatened, and indeterminate species discussed above. The Advisory Committee also recommended to the Fish Commission that commercial hunting be outlawed and that all organised rattlesnake hunts be required to release their snakes. The Pennsylvania Fish Commission derives its authority to make regulations concerning reptiles from the Pennsylvania Fish Laws, section 251 which states: 'The Executive Director (of the Fish Commission), with the approval of the Commission, may promulgate rules and regulations governing the taking, catching, killing and possession of all amphibians and reptiles and in addition may establish seasons and possession limits for all amphibians, reptiles and aquatic organisms.' The same section provides for a $20-00 fine for every regulation broken and a $10-00 fine for each specimen illegally in possession (Purdon's Pa. Statutes Annotated, 1976). In April, 1977, the Fish Commission's Board of Commissioners met, but the Advisory Committee's recommendations to require rattlesnake hunts to release their snakes or to outlaw commercial sales were not even considered. The Commission has advised us that the regulation of the sale of amphibians and reptiles, will require further legislative action. The Commissioners did adopt a regulation prohibiting the destruction of dens and approved a list of endangered, threatened, and indeterminate fishes, amphibians and reptiles. Future regulations must deal with the direct destruction of snakes by commercial hunters and 'sportsmen'. Consideration must be given to the effects of activities which do not kill the snakes immediately but may have drastic effects upon them later. Fitch and Glading (1947) and Fitch (1949) found that many rattlesnakes (C. v. oreganus) in their study lost weight after being handled. Weight loss was apparent in some snakes more than two years after being handled. Wharton (1966) reported similar results with cottonmouths (Agkistrodon piscivorus) although he only handled the snakes for five minutes. There is also evidence that snakes disturbed in an area will abandon that area (Fitch, 1960; Wharton, 1966). If snake hunts are to be allowed to continue, studies must be undertaken to examine the long-range effect of the extensive handling the snakes receive during the hunt. The movement and survival of snakes released into new areas must also be investigated further, since most of them may die during the winter. For 75 years the Carnegie Museum in Pittsburgh has been collecting records of the distribution of snakes in Pennsylvania. These data show that the total range of

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the timber rattlesnake in Pennsylvania has decreased drastically (Dr C. J. McCoy, personal communication). Because rattlesnakes reproduce slowly they take a long time to recuperate from extensive hunting. Woodbury and Hansen (1950) reported on one population of rattlesnakes at a den hunted very heavily for one year which still had not recovered 12 years later. In a study on Great Basin rattlesnakes (C. v i r i d i s ) , Parker and Brown (1974), reported on the devastating effect of gathering snakes at the dens when they are aggregating. They concluded that recovery of former population size is a long-term process. As rattlesnakes decline, the number of people becoming active in snake hunting is increasing. Habits such as denning in winter and the aggregation of females when gravid can subject a population of rattlesnakes to heavy losses. If numbers of gravid females are captured when they aggregate in late summer, a large part of the reproductive potential could be lost, even though a relatively small part of the total adult population is removed. One of the best ways to save the timber rattlesnake is by education of the public to ignore old prejudices and to look at the rattlesnake as they would any other wild animal. However such a process of education will take generations. Many people in rattlesnake country find it easier to believe in myths told to them by trusted neighbours and relatives than in facts assembled by 'outsiders'. In view of the time such an educational programme would take relative to how fast the timber rattlesnake is declining, the only feasible solution is the adoption of protective laws. Currently much of the best rattlesnake habitat in Pennsylvania is on state and federal lands. Immediate protection of rattlesnakes on these public lands in combination with a prohibition of commercial sales, bounties and organised hunts, would do much to check the snake's decline.

ACKNOWLEDGEMENTS This study was supported in part by grants from the Western Pennsylvania Conservancy and the Pennsylvania Fish Commission. We gratefully acknowledge the assistance of Peter Saber, David Galligan, and Edwin Leid in the field. Rick Swarts and Martin Boraas assisted with the statistical analyses, and Marianne Galligan helped in numerous ways.

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