Temperature regulation, body weight and changes in total body fat of the free-tailed bat, Tadarida brasiliensis cynocephala (Le Conte)

Camp. Biochem. Physiol., 1975, Vol.

50A,pp. 231 to 246. Pergamon Press. Printed in Great Britain

TEMPERATURE REGULATION, BODY WEIGHT AND CHANGES IN TOTAL BODY FAT OF THE FREETAILED BAT, TADARIDA BRASILIENSIS C YNOCEPHALA (LE CONTE) JOHN F. PAGELS* Department of Biology, Tulane University, New Orleans, Louisiana, U.S.A.

(Received 13 November

1973)

Abstract-l. Resident Tad&da brasiliensis cynocephala in New Orleans, Louisiana, on colder days formed denser clusters in more protected areas of the roost. 2. Resistance to hypothermia during cold exposure was least in summer, intermediate in early autumn and greatest in late autumn. 3. In autumn months female bats resisted hypothermia longer than male bats. 4. Length of survival at ambient temperatures of 6-7, 15-16 and 22-25°C increased from autumn through winter, and female bats always lived longer than male bats. 5. Greater resistance to hvnothermia and areater survival by Tudarida in cool months are correlated __ with greater fat stores.

INTRODUCTION INTERSPECIFICand intraspecific differences in the thermoregulatory abilities of bats have become increasingly evident in recent years. Additionally, data for several species stress the importance of such factors as sex, season, reproductive condition, nutritional state and acclimatization in the thermoregulation of a given species (Han@ 1959; McNab, 1969; Henshaw, 1970; O’Farrell & Studier, 1970; Rasweiler, 1973). Two subspecies of the free-tailed bat, Tadarida brasiliensis, occur in the United States. The western subspecies, T. b. mexicana (Saussure), migrates and it is absent from much of its northern range in winter months (Glass, 1958, 1959; Davis et al., 1962; Villa & Cockrum, 1962). Many studies have been made concerning thermoregulation in T. b. mexicana (Twente, 1956; Henshaw, 1960; Herreid, 1963a-d, 1967; Licht & Leitner, 1967). Little is known about temperature regulation in the eastern subspecies, T. b. cynocephala (Le Conte), a form that is resident in New Orleans, Louisiana (Pagels, 1972). Lava1 (1973) recently provided information, including some data on temperature regulation, for T. b. cynocephala in Baton Rouge, Louisiana. In New Orleans Tadarida roosts in homes, warehouses and other suitable structures and it is often directly exposed to changes in ambient temperatures. Field and laboratory investigations of the biology of temperature regulation in T. b. cynocephala, * Present address: Department of Biology, Virginia Commonwealth University, Richmond, Virginia 23220, U.S.A.

primarily in response to cold, are discussed in this paper. Included is information on seasonal and sexual differences in resistance to hypothermia at various ambient temperatures, and annual total body fat and weight cycles. MATERIALS AND METHODS Most bats used in the temperature studies were mistnetted as they emerged from a private home in downtown New Orleans, Louisiana. Bats roosted high within the walls and attic of the house. The nature of the roost and lack of crawl space precluded observations on clustering and associated activities. Additional bats were collected by hand at a warehouse (Pagels, 1972). The narrow roost area on the outside of the warehouse facilitated observations of relative cluster compactness and movements within the roost. Air temperatures (T,) in the roost area were gathered by attaching probes (YSI Model 44TD Thermistor Tele-thermometer) in the roost area. Due to frequent movements of the bats and the height of the roost it was difficult to measure temperatures within clusters. Some rectal temperatures (Tb) of bats were obtained by removing bats and carrying them to the dock below. The procedure required 1530 set and an increase in Tb during this handling was probably negligible. Additional temperature data were obtained from the U.S. Weather Bureau in downtown New Orleans. Bats were sampled twice a month at the warehouse for determination of body weight and total fat present. No collections were made in August. The bats were taken between 0700 and 1100 hours and maintained alive for about 2 hr. In the laboratory the bats were killed, sexed, weighed and kept individually in plastic bags for later analyses. Determinations of total fat were made using Soxhlet with chloroform-methanol Extraction Apparatuses 231

JOHN I?. PAGELS

238

(2 : 1) as the solvent. Prior to extractions the gut contents were removed and the animals weighed again. Fat indices (g of fat/g of lean dry weight) and water indices (g of water/g of lean dry weight) were determined for 174 bats.

Laboratory temperature studies

Observations were initiated on several dates to determine the ability of the bats to resist hypothermia or maintain homoiothermy in different seasons and at several ambient temperatures. Bats used on 26 December 1967 were collected at the warehouse the morning that the experiment was started. All other bats were mistnetted at the home on the evenings before observations were initiated. Only bats emerging from the roost were taken, hence by the next morning all bats had fasted for at least 24 hr. Bats were weighed prior to cold exposure. Bats were contained in 05-l. cardboard cans in all studies. ?j,‘s were measured as the animals were placed in the temperature units and thereafter every 24 hr during the first 10-12 hr of exposure. Rectal temperatures were measured at a depth of 1.5 cm using a Tele-thermometer small animal probe. Bats were exposed to Ta’s of 6-7°C on seven dates, and on four dates additiona bats were exposed to T,‘s of 15-16 and 22-25°C. Eight to ten bats of each sex were used in all observations except 26 December 1967 when only seven females were used. In three studies after recording the T,_,‘sin the first 10-12 hr the bats were checked daily and kept in the temperature units without food or water until they died. In addition to the bats used in the experiments of September, October and December 1969, ten bats of each sex were killed imm~jately after capture to determine total fat present on these dates and to provide additional data on seasonal changes in total fat.

Table 1. Relationship Roost temperature (“C) Date 1968-69 23 September 30 September 17 October 24 October 5 November 11 November 27 November 16 December 3 January 6 January 27 January 26 February 9 March 26 March

Near

In

28.5 27.0 27.0 19.0 15.0 11.0 22.0 4.0 9.0 40 13.0 13.0 7.0 14.0

335 27-O 27.0 240 17.0 11.0 21.0 4.0 9.0 4.0 15.0 -

RESULTS Observations at the railroad warehouse from October 1967 to March 1969 reveaIed no decrease in the number of bats present during the winter months. In February 1968, the coldest February in

New Orleans since 189.5, minimum T.‘s 5°C or lower were recorded on twenty-three days and on five of these days the T, dropped to 0°C. Cluster compactness and area of the roost used at the warehouse reflected TB’s. In general appearance bats were closely associated on all days (Table 1). On warm days bats were in a single file pattern along most of the roost area and usually at flight temperature, 30°C or above (Pagels, 1972). On cooler days clusters were formed in less exposed areas of the roost. On 26 March 1969, for example, T, near the roost was 14°C. Most bats were in clusters and most were at flight temperature. Bats roosting individually were cold and none checked was capable of flight. On the coldest days most clusters of bats were very dense, and only the most protected areas of the roost were used. Because of the density of the clusters it was difficult to remove bats. Even on coldest days a few individuals or small groups roosted in less protected areas. Body weights of maie bats collected at the railroad warehouse (Fig. 1) were more irregular and demonstrated less seasonal variation than body weights of female bats. The low female weights in March of each year matched dates vaginal plugs were found (Pagels & Jones, 1973). The sharp increase in female weight after March was due to pregnancy.

between air temperatures

Roost section used

Cluster compactness Loose

Moderate X

X

X

X

X X

X

X

and flight abilities of bats

Dense

Narrow

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

* See text. Area of roost used, and relative cluster compactness Observations were made between 0730 and 1000 hours.

Moderate

Wide

X X

X

X

X

X

X

X

Bats at flight temperature Yes Yes Yes Yes No No No No No No No No No Some*

at the time of each visit are indicated.

Resistance to hy~the~ia

I

AugSept Ott

b

I

NW

:

I,

Dee

Jon

in the free-tailed bat

Fcb

/

’

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Mar

Apr

May

9

June

239

I

July

Fig. 1. Mean body weights of male and female ZWurida. Circles designate weight from October 1967 to October 1968; x from October 1968 to March 1969. Except where noted in parentheses mean represents six or more bats.

Fig. 2. Fat indices of individual male and female Tudarida. Open circles designate November 1967May 1968; closed circles designate September-December 1968. Indices of fat extracted (Fig. 2) more closely reflected expected seasonal changes than did actual body weight. The apparent discrepancy between body weight and fat indices of animals collected and weighed in the morning before gut contents were removed reflects periodic feeding in winter months. There was little variation in lean dry weight (fresh weight minus fat and water). Lean

dry weight of males was slightly higher, but not sign%cantIy different than lean dry weight of female bats. Means and 95 per cent confidence limits of lean dry weights for female and male bats were 3.25 + O-31, and 343 + 044, respectively. In addition to changes in body weight, evidence for feeding during winter was determined by examining stomachs of animals cohected. A few

JOHNF.

240

bats contained some insect remains on all winter dates; however, amounts of insect remains were not measured. Although I have no activity data for the coldest nights, I observed bats flying on all evenings that I visited the roosts during the winter months of 196869. The bats typically disappeared after emergence. On 3 February 1969 activity at the roost in the private home was atypical. In mid-day T, rose to 21°C but by 2000 hours the T, had dropped to 10°C. Bats were observed flying at both the home and the warehouse. At the home the bats were very noisy, but instead of emerging and immediately disappearing from sight as was the usual case, many bats emerged only to return to the roost site in a few seconds. Thus, in the period of observation there were many bats flying around the opening of the roost, with many bats emerging and others returning at the same time. Later in the evening the minimum T, recorded was 55°C. R. Davis et al. (1962) observed similar behavior in T. b. mexicana in Sinton, Texas, on a cool winter evening.

PAGELS I 40 t 30 20 1 IO-

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Mean Tb’s of male and female bats during the first day of exposure to T, 6-7°C are indicated in

0

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3 4

30 July -_._.__8 July

5 6 7 8 3 IO II

12

Time

Fig. 4. Rectal temperatures of female Tadurida exposed to ambient temperatures of 67°C on fist day of each experiment. See Fig. 3 for explanation. ____ _

I 9

c

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om

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Fig. 3. Rectal temperatures of male Taduridu exposed to ambient temperatures of 6-7°C on first day of each experiment. The horizontal line represents the mean and the vertical line indicates the range. The rectangles designate 95 per cent confidence limits of means.

Figs. 3-4. Females resisted hypothermia longer than males on all dates except 9 and 30 July. Both male and female bats resisted hypothermia longer in October and December than on other dates. Female bats used in the 26 December 1967 experiment exhibited the greatest and most uniform resistance to hypothermia. Beginning in September male resistance increased on successive dates, with greatest resistance demonstrated on 10 December. Females also resisted least during summer months; however, except for 26 December 1967, female resistance to hypothermia was greatest on 15 October. The responses of the bats on the first day of exposure to T, 15-16°C are similar to those at T, 6-7°C. At T, 15-16°C the least resistance to hypothermia by both male and female bats was in July and September, and the greatest resistance to hypothermia occurred in October. Male and female responses to Ta’s 15-16°C were similar in July and September, although female resistance to hypothermia was greater than male resistance in October and December. The pattern of response to exposure to T, 22-25°C was similar to that at lower temperatures. Except that both males and females were slightly more thermolabile on 8 July, there were virtually no seasonal or sexual differences in response to 22-25°C.

Resistance to hypothermia in the free-tailed bat Combined body weights of experimental bats measured before the start of the temperature observations are given in Fig. 5, Greater resistance to hypothermia at each of the experimental temperatures can be correlated with greater body weight, i.e. fat deposits, on all dates except 10 June and 9

241

given in Table 2. Bats demonstrated sexual differences in survival similar to differences in resistance to hypothermia and amounts of fat deposited. Note (Table 2) that (1) female ~~~u~j~~ survived longer than males in each situation, (2) in September and October bats lived longest at r, 1%16°C but in

, 6,4

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Fig. 5. Mean body weights of experimental bats at the start of each experiment. Numbers designate number of bats used. Vertical lines designate range, heavy horizontal line is the mean and rectangles enclose 1 S.E. July when bats demonstrated little resistance to hypothermia although relatively heavy. Female bats weighed more in October than male bats. Figures 1 and 2 depicted the annual change in body weight and the mounts of fat deposited. Fat indices of the ten males and ten females kitled immediatety after capture on 4 September, 15 October and 10 December are presented in Fig. 6. Statistically significant least-squares equations for predicting fat index (FI) from body weight (BW) are presented in Fig. 7. The standard errors reflect individual variation in the lean components as well as differences in the amount of water present. I have not presented the water indices of bats collected throughout the year; however, water indices of the aforementioned Tadarida killed after capture in September, October and December are presented in Fig. 8. As in several other species of bats there was a tendency for water indices to complement increases in fat indices (Baker et al., 1968; Ewing et al., 1970; Krulin & Sealander, 1972). As noted, I kept animals in the 4 September, 15 October and 10 December studies at each of three temperatures until they died. Weights of bats at the start and the number of days lived at each exoerimental temoerature on the three dates are 1

I.60

I ,40 i_

I IO Dee Fig. 6. Fat indices of bats killed before start of experime&s on the dates indicated. See Fig. 5 for explanation. I

0:

242

JOHN F. PAGELS

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2.60-

2.50-

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Body

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Fig. 7. Fat index (FI) as related to body weight (BW) in male (N = 30) and female (N = 30) Tadarida (2 1 SE.). 2.10-

December at T, 6-8”C, (3) a notable increase in survival of females at T, 1516°C on 15 October and (4) in males a notable increase in survival did not occur at any temperature until 10 December. As expected from the relationship between body weight and fat indices, survival and body weight are linearly related. The significant least-squares regression equations are plotted in Figs. 9 and 10 for male and female bats, respectively. The weights of the bats at death were also interesting from the standpoint of seasonal and sexual differences (Fig. 11). Weight loss was greater at the higher T,‘s, but female bats lost slightly more weight than males at all Ta’s.On 10 December weight loss at each T, was slightly more than in September and October, especially at the lowest T,.

Table 2. Relationships

1

I 4

I

15 ._ Ott

sept

IO

Dee

Fig. 8. Water indices of bats killed before start of experiments on the dates indicated. See Fig. 5 for explanation. DISCUSSION

Tinkle & Patterson (1965), Henshaw & Folk (1966), Herreid (1967), Licht & Leitner (1967) and Henshaw (1970) discussed clustering and reviewed much of the earlier information on microhabitat

between body weights and the number of days that Tadarida lived at each ambient temperature 15-16°C

67°C 4 September

2.00-

15 October

10 December

4 September

15 October

22-25°C 10 December

4

15

10

September

October

December

Females 8 Wt start

12.0 13.2 13.9 11.4 13.4 13.4 12.0 13.0 13.6 (10.7-13.5) (12.8-15.0) (13.1-15.1) (10+12*6) (12.2-15.6) (11.7-14.3) (10.7-13.6) (11.5-14.1) (12.5-14.4) X Days lived 15.3 19.5 52.0 19.0 34.0 38.0 12.0 17.0 22.3 (11-22) (20-82) (12-64) (9-16) (2-28) (13-27) (39-63) (12-24) (12-32)

Males B Wt start

12.0 12.6 13.7 12.0 12.6 13.4 (11.612.5) (114-13.9) (10.8-14.7) (110-12.9) (11.6-13.7) (llG15~1) B Days lived 38.1 15.1 18.0 34.0 (14-20) (13-25) (13-47) (1661) The ranges are in parentheses.

11.9 12.3 13.7 (10.8-12.5) (110-13~5) (12.4-16.9) 9.7 11.6 21.5 (2-13) (3-17) (11-29)

Resistance to hypothermia 100

in the free-tailed bat

243

r

”

IO

I

II

12

13

Body

14

weight

15

16

17

(BW)

Fig. 9. Number of days male bats lived (DL) at air temperatures indicated as related to initial weight (BW). At 6_7”C, DL = 9.884BW - 108.373 rf:12.75; 15-16”C, DL = 6*3386BW -58.008k 9.310; 22-25X, DL = 3.4552BW - 29.016k 4.60.

Body

weight

(SW)

Fig. 10. Number of days female bats lived (DL) at air temperatures indicated as related to initial (BW). At 6-7”C, DL = 12_273BW- 130.88+ 12.172; 15-16”C, DL = 10052BW-98.97k9.07; 22-25”C, DL = 3.1190BW-22.818k5.3021.

weight

6-7 0

b?

I4 t

15-16

“C ,.

‘C

22-25

“C

10’0

IO

II IO

-

-

Fig. 11. Summary of relationships among body weights at the start and end of experiments on the dates and at the ambient temperatures indicated. The tops of the bars designate the mean weight at the start, and the horizontal line below the top indicates the mean weight at death.

244

JOHN F.PAGELS

selection and the role of clustering in bats. In this study the nature of the open roost at the warehouse in New Orleans (Pagels. 1972) afforded T. b. cynocephala protection from wind, rain and direct sunlight but did little to alter daily and seasonal temperature extremes. Differences in TB’s were manifested in clustering behavior; that is changes in size, compactness and locations of the clusters. In cave dwelling forms the clusters and the caves act as buffers against temperature extremes. Greater cluster density and locations of clusters in more protected areas on cold days appears to reflect an initial attempt by T. b. cynocephala to decrease exposed surface area, that is to decrease conduction and maintain high T,,‘s. This suggestion is supported by observations that the clusters were much looser in warm weather, and the laboratory observations that Tadarida is able to resist hypothermia, or maintain a large body-to-ambient-temperature differential for relatively long periods during winter months. Herreid (1967) observed that metabolic rate is a function of cluster size, i.e. larger groups had lower rates. Although I did not measure metabolism, it is likely that with decreasingly low TB’s heat production decreases greatly as the Tb’s begin to drop near the T,, or the converse. The dense clusters would then aid in conserving the small amount of heat produced under the hypothermic conditions. Twente (1956) found that in cool surroundings some T. b. mexicana in clusters elevated their Tb’s but did not fly resulting in a cluster temperature somewhat higher than that of the surrounding air. Under laboratory conditions not all T. brasiliensis demonstrate the ability to arouse from low Tb when in cold T&k. In my laboratory studies an occasional bat that had been hypothermic for several days was found very active while still contained in the cold chamber. Herreid (1963a, 1967) made similar observations on T. b. mexicana in laboratory studies. If Tadarida behaves in a similar fashion under natural conditions, a dense cluster may function in at least a couple of ways during the arousal period. Arousing bats may physically stimulate cold neighbors by activity and noise. Perhaps not related to clustering or arousal, Herreid (1967) found in cave measurements that bats in metabolism chambers elevated metabolism in response to the noise of bats flying near the chamber. Another function of the cluster in arousal is that cold bats may rewarm to more irritable Tb’s from heat conducted and radiated from adjacent arousing bats. Winter movements, such as by Tadarida in New Orleans, is not unique among bats. Movements among and within hibernacula have been noted in hibernating bats (Folk, 1940; Griffin, 1940; Mumford, 1958; Jones & Pagels, 1968; and others) and Fenton (1970), Henshaw (1970), Krulin & Sealander (1972) and Pagels & Blem (1973) present discus-

sions on the possible costs of such activity on the energy reserves of bats. Unlike hibernating vespertilionids that apparently lose weight at a relatively constant rate during hibernation (Beer & Richards, 1956; Mumford, 19.58; Troyer, 1959) the winter activity of T. b. cynocephala in New Orleans is evidenced in variable body weights in winter months. In addition to diurnal weight changes associated with feeding, weight increase of bats prior to hibernation or migration and weight losses reflect changes in amounts of fat present. With more information becoming available on bat activity, metabolism (including metabolism during flight), data on energy stores will play an increasing role in assessing the overall fitness of populations of bats. For example, on the basis of body weights of Eptesicus fuscus collected during the fall and spring in Minnesota, Beer & Richards (1956) estimated E. fuscus could live under relatively constant hibernating conditions in a cave for 194 days, very close to the frost period in the vicinity of St. Paul, Minnesota. Such estimates for T. 6. cynocephala in New Orleans are presently impossible because of variation in T&‘s and consequent periodic feeding and weight changes. Compared to body weights of T. 6. mexicana in the fall in Kansas (Twente, 1956) and Texas (Herreid, 1963b) it seems the amount of fat deposited by T. b. cynocephala would be great enough to support migratory flights. At all times of the year T. b. cynocephala had lower fat indices than the levels reported for T. b. mexicana collected in March in New Mexico (Weber & Findley, 1970). Weber & Findley stated that the high fat indices in March in Tadarida are necessary for spring migration. Although interspecific, geographical and individual differences should be expected in fat deposition, the seasonal differences reported herein for T. 6. cynocephala are similar to the annual cycle of the gray bat, Myotis grisescens (Krulin & Sealander, 1972), and the seasonal components reported for several other bat species (Baker et al., 1968;Ewing et al., 1970; Weber & Findley, 1970). Greater fat deposits in female Tadarida are similar to the observations of Ewing et al. (1970) and Krulin & Sealandei (1972). Pearson et al. (1952), Cox (1965), Dwyer & Hamilton-Smith (1965), Stone & Wiebers (1965), Tinkle & Patterson (1965) and Dwyer & Harris (1972) provide additional discussion on the thermoregulatory activities of female bats, that in large part relate to various aspects of the reproductive cycle. In warm seasons T. b. cynocephala was at a highly unnatural T, when placed in a cold unit at 6-7°C and members of each sex demonstrated little ability to maintain high T,,‘s. During the winter the temperature responses of T. b. cynocephala were unlike those of vespertilionids inhabiting temperate regions. Several recent studies have indicated that in addition to the weight and lipid changes discussed above,

Resistance to hypothermia in the free-tailed bat there are physiological and behavioral differences between hibernating bats in daily lethargy, i.e. diurnation, and hibernating bats in hibernation (Menaker, 1961, 1962; Dwyer, 1964; Stones & Wiebers, 1965; Henshaw & Folk, 1966; W. Davis et al., 1967; O’Farrell & Studier, 1970; and see Henshaw, 1970). Briefly, in hibernating bats the physiological and behavioral changes result in seasonal compensation for low T, and low or absent food supply by reduction in metabolism with Tb near T,, but with an increased ability to actively arouse from low Tb. In laboratory studies Tadark& demonstrated seasonal differences in temperature responses more like that of homoiotherms that undergo seasonal acclimati~tion. In warm seasons when migratory T. b. mexicana is found in Texas, T,,‘s of bats in cave habitats are usually high despite a wide range of T*‘s (Herreid, 1963c), and the present study indicates that the ability of T. b. cynocephala to resist hypothermia is greater during the winter. Henshaw (1970) noted that certain species of homoiothermic bats can tolerate hypothermia very well. Tadarida in this study also demonstrated increased survival while in hypothermy, and that the length of survival is related to the amount of stored fat. Migratory T. b. mexicana when placed under hi~r~ting conditions lived only one-fourth to one-third as long as hibernating species of vespertilionids placed under the same conditions (Herreid, 1963b). Herreid suggested that Tadarida was unable to completely utilize energy (fat) reserves at hibernating conditions. In all laboratory observations the lowest body weights at death were at T, 22-25°C; weight loss at T, 1516°C was inte~ediate, and the least amount of weight was lost at T, 6-7°C. Presumably weight loss reflected use of energy stores and/or water. It should be noted that prior to death some of the bats that had lost excessive amounts of weight probably would not have been capable of arousing to flight temperature (Pagels, 1972). An increase in length of survival at T, 1516°C in September and October demonstrated that lower Ta’s and a decrease in Tb,, despite lengthy resistance to hypothermia, is effective for greater survival during periods of cold stress. On 10 December weight loss was greater at all Ts’s than in observations initiated on earlier dates, especially at the lowest T,. These data suggest an increased ability to utilize energy reserves at lower temperatures and a drop in the optimum temperatures for maximum survival in hypothermy. Although Tadarida is resident in New Orleans, it is possible that in certain winters it may move; this is evident at least in certain parts of its range. Sherman (1937) in a study over several years, found upwards of 10,000 T. h. cynocephala in a colony in Gainesville, Florida, in the summer months, whereas only several hundred remained throughout the winters. Sherman noted that the winter of

245

1934-35 was severe, and that only a few bats were in the building that winter. Bailey (1951) studied an attic colony of T. b. cynocephala in Baton Rouge, Louisiana, in the fall and early winter of 1950. Bailey observed about 20,000 bats on 23 September, a noticeably reduced number on 15 October and no bats on 17 December. However, Lava1 (1973) reported T. 6. cynoeept~a~a as apparently resident in Baton Rouge. T. b. cynocephala may be described as being neither a hibernator nor a good homoiotherm, but a bat that enjoys certain of the assets of each thermoregulatory pattern. For the present, Tadaridu seems well adapted for overwintering in Louisiana, a state that is as described by Dyke (1941) in the colder season “. . . alternately subjected to tropical air and cold continental air, in periods of varying length’. Acknowledgements-Much of this work was a portion of a dissertation submitted to the Graduate School of Tulane University in partial fulfillment of the requirements for the degree of Doctor of Philosophy. I am grateful to Drs. CIyde Jones and Norman C. Negus who provided advice and support throughout the study. I thank Dr. R. D. Suttkus for his encouragement and also for support through a National Institutes of Health Environmental Biology Training Grant (No. S-TOIESOO27). Additional support was received from a National Aeronautics and Space Administration Fellowshio. Dr. Francis L. Rose orovided sueeestions on methods of fat extraction. I g;atefuIly acknowledge Dr. Keith Grisham, Frank Thomas, Frederick Jannett and Robert Cashner for assistance in the collection of bats. Drs. R. R. Mills and C. R. Blem read the manuscript and offered helpful suggestions. I also thank Dr. Blem for numerous discussions on thermoregulation in vertebrates and for assistance in analyzing the data. RETRACES BAILEYF. (1951) Observations on the natural history of the freetailed bat, Tudaridu cynocephala (Le Come). Thesis, Louisiana State University at Baton Rouge. BAKERW. W., MARSHALLS. G. & BAKERV. B. (1968) Autumn fat deposition in the evening bat (Nycticeius hutneralis). J. Mammal. 49, 314-317. BEERJ. R. & RICHARDSA. G. (1956) Hibernation of the big brown bat. J. ~a~r~?zai.37, 3141. Cox T. J. (1965) Seasonal change in the behavior of the western pipistrelle because of lactation. J. Mammal. %, 703. DAVIS R. B., HERREIDC. F., II & SHORT H. L. (1962) Mexican free-tailed bats in Texas. &al. Nonogr. 32, 31 l-346. DAVIS W. H., CAWEINM. J., HA~~ELLM. D. & LAPPAT E. J. (1967) Winter and summer circulatory changes in refrigerated and active bats, Myotis ~UCI$&K J. MammaI.48,132-134. DWYER P. D. (1964) Seasonal changes in activity and weight of Mi~iopterus sc~re~bersi ~[epotis (Chiroptera) in northeastern New South Wales. Aastral. J. 2001.12, 52-69.

246

JOHN F. PAGELS

DWYER P. D. & HAMILTON-SMASH E. (1965) Breeding

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Key Word Index-Chiroptera; Molossidae; Tadarida brasiliensis cynocephala; bats; clustering; body weight; total body fat; body temperature; hypothermia; temperature regulation.