Scent-marking in lone wolves and newly formed pairs

Anim. Behav., 1979, 27, 750-760

SCENT-MARKING IN LONE WOLVES AND NEWLY FORMED PAIRS BY RUSSELL J . ROTHMAN & L . DAVID MECH* Department of Ecology and Behavioral Biology, University of Minnesota, Minneapolis, MN 55455 and Patuxent Wildlife Research Center, U .S . Fish and Wildlife Service, Laurel, MD 20811

Abstract. Scent-marking was studied in wolves (Canis lupus) along 133 km of tracks in northern Minnesota during winters of 1975 to 1976 and 1976 to 1977 and in two captive packs and four captive pairs for various periods . Lone wolves, which possess neither mates nor territories, rarely marked by raised-leg urination and defaecated and urinated less along roads and trails, where territorial pairs and packs generally marked . Newly formed pairs marked the most, eventually decreasing their rates to those of established packs . Generally, wolves that scent-marked also bred, whereas non-marking wolves usually did not breed . Scent-marking apparently is important to the success of courtship in new pairs and to reproductive synchrony in established pairs, as well as serving a territorial function . Considerable speculation has centred upon the socio-ecological functions of scent-marking in canids (Kleiman 1966 ; Anisko 1976 and reviews therein) . In wolves, the primary means of scentmarking is by urination (Peters & Mech 1975) . Sexually immature and subordinate wolves of both sexes generally squat-urinate (SQU), but dominant pack animals usually raise-leg urinate (RLU) (Peters & Mech 1975) . Raised-leg urinating clearly fills Kleiman's (1966) criteria for scent-marking, and appears to be strongly related to territorial possession (Peters & Mech 1975) . For an understanding of the context of scentmarking, we provide the following summary of wolf social biology in the study area . Wolf packs inhabit exclusive, relatively stable territories of from 125 to 310 km2 each (Mech 1973, 1974) . Packs include a dominant adult male and female, the alpha pair, which generally direct the pack's activities (Mech 1970) . The other members are subordinates, usually the offspring of the alpha pair, some of which may disperse from the pack and become lone wolves (Mech 1972, 1973) . Generally, loners travel along the periphery of territories (Mech 1972, 1973) and occasionally cover areas of as much as several thousand km 2 per year or disperse as far away as 224 km (Mech, unpublished) . If caught in a pack's territory, loners are sometimes chased and killed (Mech 1970,1977 ; Van Ballenberghe & Erickson 1973) . Lone wolves must establish a pair bond and a territory to reproduce . We would predict, then, that lone wolves, which are nomadic and without territories (Mech & Frenzel 1971 ; Mech 1973), would not

scent-mark, although this question had not been studied . It was known that one new pair, formed from lone wolves of opposite sex, scent-marked at an especially high rate (Peters & Mech unpublished) . Nevertheless, whether all such pairs mark so intensively has not yet been determined . Besides urination, defaecation and scratching can also serve as scent-marking in wolves (Peters & Mech 1975) . Scats often are left at conspicuous locations such as on rocks and at trail junctions . Scratching, the alternate movements of the stiffened limbs, often occurs after defaecation or a RLU . It has not been reported to follow a SQU and is performed predominantly by high-ranking males (Peters & Mech 1975 ; this study) . Whether lone wolves use defaecation and scratching to mark has been unknown . Thus several unanswered questions about scent-marking emerge . Do lone wolves of either sex scent-mark? If so, at what age and under what conditions? If not, when does scentmarking begin, and what induces it? What is the relationship between scent-marking and locating and securing a mate and territory? Do most newly formed pairs mark at high rates? If so, why? This study attempts to answer these and related questions . Methods Field aspects of this study were conducted in a 2500 km 2 area of the Superior National Forest in northeastern Minnesota, 92° W . longitude, 49 ° N . latitude . The topography is relatively flat, with low ridges . Lakes comprise over 15 of the area . Annual snowfall averages 145 cm and the growing season is about 100 days ; annual temperatures range from -46 to 36 C (Ohmann & Ream 1971) . The area is in the southern extreme of the northern coniferous

*Present address : North Central Forest Experiment Station, 1992 Folwell Avenue, St . Paul, Minnesota 55108 . 750



ROTHMAN & MECH : WOLF SCENT-MARKING

biome (taiga) of North America (Odum 1971) . Logging roads criss-cross the region . Field investigations were conducted during winters of 1975 to 1976 and 1976 to 1977 and were based on ground tracking (via snowshoes, skis, and vehicles) of 11 identified single wolves or newly formed pair members plus their mates (Table I) . The animals tracked had been radiotagged as part of a continuing investigation of wolf socio-ecology (Mech in press and refs . therein), and were located from the air each day, weather permitting . Urination postures were determined from the position of urine marks in the snow . Steps were counted by a hand-held counter, and the following data were recorded : type and age of mark, location, number of wolves, travel direction, type of trail, gait, investigations, RLU targets, distance between marks, presence of kills, and meteorological information . Photographs were taken, and samples of marks were frozen for laboratory analysis . We estimated the quantity of urine in each mark after practice at accurately estimating volume of liquid in marks made by yellow-dye-filled syringes . RLU's were defined as urine marks found only on vertical objects, and SQU's as urine on the snow surface. Because some RLU's can also leave urine on the surface, as seen in captive packs, some marks recorded as SQU's in the field may

actually have been RLU's . With captive wolves, RLU's and SQU's were distinguished by observation of the actual leg position . While tracking pairs of wolves, it was impossible to determine which member made which scent-mark . Both SQU and defaecation probably were performed equally by male and female pair members, as verified by observations of captive wolves . Thus all loner/newly formed pair comparisons were based on SQU and scat rates per individual . However, observations of captive animals indicated that production of both RLU's and scratches were probably malebiased, so those rates were calculated per pair . This is in keeping with the reporting of marking rates in wolf packs (Peters & Mech 1975) . The U .S . Fish and Wildlife Service's captive wolves near Minneapolis were also studied during the summer and fall 1976 and winter 1976 to 1977 . Data were collected on scentmarking rates and reproductive behaviour in four pairs of wolves (not necessarily pair-bonded), a pack of seven adults ('North Pack') and a pack of six adult and maturing wolves ('South Pack') Seal et al . in press) to supplement the field studies and to aid in their interpretation . Location data from radio-tracking lone wolves from 1974 to 1977 were analysed for insight into movement patterns immediately preceding pairing with a wolf of the opposite sex .

Table 1 . Summary of Individual Histories of Radio-tagged Wolves Tracked during Study

Wolf

Sex

Age at beginning of study (yrs)

Loners 353

F

1 .6-3 . 6

5131 5429

F F

6-10 1 .6-3 . 6

5139

F

5190 5421

M M

1 .6 1 . 6-3 . 6

Pairs 5430+1

F

1 . 6-3 . 6

5401 5071

M F

1 . 6-3 . 6 3 . 6-5 . 6

5132 5176

M F

4-6 2.6

353+1 5139+1

1-6

751

Social status Lone wolf, paired in late fall 1976 and set up territory Lone wolf Strayed from pack at times, but never permanently dispersed Member of newly-formed pair, Nov . 1975 to Nov. 1976, when mate was no longer seen with her Same as 5429 Lone wolf Lone wolf, paired in Jan . 1976 and set up territory

Although a littermate of 5139, 5176 was not studied until Jan . 1977, one year after 5139 was studied See above See above



752

ANIMAL BEHAVIOUR, 27, 3 Table II. Comparison of Data Obtained by Ground Tracking Lone Wolves and Newly Formed Pairs, 1975 to 1977 Roads and trails Marks Dist . (km) tracked Type*

Lone wolves

33 . 4

Newly formed pairs 36 .0

RLU SQU SCT

No .

Per km

0 0.0 4 0. 1 1 0 .0

RLU 107 SQU 17 SCT 10 SCR 4

3.0 0.2 0. 1 0. 1

Dist . (km) tracked Type

Woods

Waterways

Marks

Marks

No .

Per km

Dist . (km) tracked

Type

No .

Per km

35 . 3

RLU SQU SCT

4 9 6

0.1 0.3 0.2

3 .5

RLU SQU SCT

0 2 4

0.0 0.6 1.1

24 . 8

RLU SQU SCT SCR

37 15 3 1

1 .5 0 .3 0.1 0 .0

0.9

RLU SQU SCT SCR

0 1 0 0

0.0 0. 5 0.0 0.0

*RLU = Raised Leg Urination ; SQU = Squat Urination ; SCT = Scat ; SCR = Scratch . RLU and Scratch rates calculated per pair ; SQU and Scat rates calculated per individual .

All comparisons discussed below without reference to statistical significance are not significantly different but are presented for their suggestive value . Results Data were collected from four female and two male lone wolves and five newly formed pairs along 133 km of tracking (Table I) . As indicated in the table, two of the animals were studied both as lone animals and as members of newly formed pairs . The youngest wolf we studied that RLU'd was paired female 5139, who was about 1 . 6 years old when we recorded RLU's by her . In addition, a lone year-old male in another study was seen RLU'ing (William Berg, personal communication) . On the other hand, two lone males at least this old, and a lone female an estimated 6 to 10 years old, did not RLU . In 72 . 2 km of tracking lone wolves, we observed no scratching and only one series of RLU's (Table II) . Lone female 353 RLU'd four times in 7 . 4 km on 4 January 1976 after probably having been chased by a resident pack . All four RLU's were in the woods even though at least half her route was along roads or trails . No significant age or sex differences in SQU and scat production was detected for loners . Although marks by strange conspecifics stimulate marking in packs (Peters & Mech 1975), no loners marked upon discovery of strange marks (n = 14) . In addition, no marks by loners were found at kill sites (n = 14), locations typically marked heavily by territorial pairs (X = 4 RLU's and 1 SQU per kill, n = 5) . Lone wolves deposited more of their scats and SQU's per kilometre in the woods or on

waterways than they did along roads and trails (Table II, Wilcoxon signed rank test, n = 6, P < 0 . 05). Initiation of Marking and Pair Formation If dispersed lone wolves are all potential breeders, each should be capable of RLU'ing, for all paired wolves we studied did . Newly formed pairs RLU'd and scratched along roads and trails at an average rate of 3 . 0 RLU's per km and in the woods at 1 . 5 RLU's per km (Table II) . The RLU rate peaked immediately preceding breeding, and increased again following breeding (Fig . 1), and the rate of RLU'ing and the period a pair had been together were inversely related (r2 = 0 . 98 ; P < 0 . 01 ; Fig . 2) . High rates of RLU'ing occurred soon after first contact between loners . In one case, lone female 353 began doing so within at most five days of first contact . Female 5430 began RLU'ing Breeding

•

Total marks

. RLU

I Squ Scat

Jan

f eo

Mor

Fig. 1 . Mean frequency of four types of scent-marks as a function of time of year in newly formed pairs in 1975 to 1976 . No data are available for 1-14 March. Breeding season determined by Mech & Knick (1978) .

ROTHMAN & MECH : WOLF SCENT-MARKING PLATE X



753

ROTHMAN & MECH : WOLF SCENT-MARKING

within at most two weeks after meeting another wolf. Furthermore, the persistence of marking apparently depends on pair members remaining together . Five pairs were temporarily separated for a total of 3 . 6 km over roads and trails and woods equally for all pairs combined . They made only one SQU and no RLU's, a rate of 0 . 1 SQU's and 0 . 0 RLU's per animal per km . In nearly 50 % of these observations, pair members RLU'd immediately before separation or after reuniting . Female 5139, who paired during winter 1975 to 1976, apparently produced and lost pups in spring and separated from her mate in early November 1976 . She remained alone through winter 1976 to 1977 . Along 4 . 7 km of tracks during late December 1976, she produced only two SQU's and two scats (0 . 4 scats, 0 . 4 SQU's, and 0 .0 RLU's per km) even though she and her mate had together been RLU'ing 3 .4 times per km one year earlier . In another instance, female 353 travelled with another wolf during January 1976 for several days in a little-used peninsula between two pack territories . During that time we found high rates of RLU'ing (4 . 8 RLU's per km) as well as tracks interpreted as mutual chasing . This pair then ventured into a nearby occupied territory and split, and 353 did not mark again in 7 . 5 km of tracking during the next three months . The next winter, when she was observed with a male, both were marking . In a more striking example, alpha male No . I of our captive South Pack, which included a

yearling male, a male pup, and three female pups, ceased RLU'ing within four days after his mate, alpha female No . 3, died accidentally in 1977 (J. M . Packard, personal communication) . He apparently performed no RLU's for the next month, even though one of the female pups courted both him and the yearling male and copulated with one of them . Previously, all of No . I's observed urinations had been RLU's . Newly formed pairs RLU'd more per km along roads and trails (84 %) than in the woods (16%, Wilcoxon signed rank, n = 6, P < 0 . 05) and packs displayed this same tendency (Peters & Mech 1975) . Four of five scratches they made were associated with a RLU or scat (Table III) . All scratches observed in the captive pack were associated with RLU's (40 %, n = 6) or scats (60 %, n = 9) . The distribution of SQU's and scats by new pairs did not differ significantly from that expected between woods and trails . However, new pairs made significantly more SQU's per km along roads and trails than did loners (Table II ; t = 2 .00, df = 6, P < 0 . 09) . Loners deposited significantly more scats in woods than did pairs (Table IV ; t = 2 . 29, df =: 6, P < 0 . 07) . Double Marking by Newly Formed Pairs `Double marking' is the phenomenon in which two marks, RLU's and/or SQU's, are made either in juxtaposition or overlapping (Plate X, Fig . 3) . Peters & Mech (1975) observed several RLU-SQU combinations and attributed them to a SQU by a female and a RLU by a male, as we did also . However, we also found male and female RLU's within 10 cm of each other from 18 Table III . Associations among Marks in Newly Formed Pairs* Type of markt

2

3 4 5 Duration of pair-bond (months)

6

Fig. 2 . The relationship between RLU rate along roads and trails and the duration of the pair bond in newly formed pairs (r2 = 0 .98, P _< 0 . 01) . Includes unpublished data from R . Peters .

RLU

SQU

RLU

22

SQU

6

1

SCT

2

2

SCR

3

1

SCT

SCR

1

*Single marks not included . Marks within 5 m of each other were considered associated, and those within 20 m of kills were excluded . tRLU = Raised Leg Urination ; SQU = Squat Urination ; SCT = Scat ; SCR = Scratch.



754

ANIMAL BEHAVIOUR, 27, 3 Table IV. Location of Scats for Lone Wolves and Newly Formed Pairs distance tracked in each location

Number of scats (%) Newly-formed pairs

Loners

Kills (within 25 m)

3 (16%)

10%)

Roads and trails

5 (28%)

13 (65%)

46%

58

Woods

9(50%)

6 (30%)

49%

40

Waterways

1 (6%)

0(0%)

5%

18(100%)

20 (100 %)

Total

December through 16 March, and they may have occurred beyond these dates but they were not observed when snow cover was absent . The rate of double-RLU'ing decreased as duration of the pair-bond increased (r2 = 0 .96, P < 0 . 01 ; Fig . 4) . Because double RLU'ing had not been reported for free-ranging wolves, no doubleRLUing data are available from packs for comparison . We also observed double-marking in the captive packs . Multiple marking was noted frequently in which one sex marked, then the other sniffed and RLU'd at or near the first mark, and the whole sequence was repeated several times . Alpha female No . 3 in the South Pack initiated 96 yo of the simple double-marks (n = 23) observed from mid-August through late October 1976 . A few of the longer sequences were initiated by the Alpha male No . 1 . Proestral Bleeding Wolves in our study area generally breed between 28 January and 4 March (Mech & Knick 1978), and vaginal bleeding may occur for as long as 45 days before oestrus (Young 1944) . We found blood in the RLU's and SQU's of our wild study animals by 4 January and at least to 24 February (Table V) . Blood appeared in 26 % of the urinations of all four newly formed pairs from 9 January to 24 February . Of the total marks produced, many must have been made by males, so the frequency of proestral bleeding in female marks alone would have been much higher than 26% . Few data were collected for lone females during this period . Investigations by Loners and Pairs All pack members inspect scent-marks, but in the captive South Pack the alpha pair made

Loners

Newly-formed pairs

Location

100%

2% 100

69 % of the investigations of all scats, RLU's, and SQU's (Table VI), including their own double-marks, single RLU's, and SQU's (Table VII) . By noting where snow was nuzzled or dug out along a wolf's trail, we found that lone wolves and new pairs made a mean of 3 to 4 investigations per km along roads and trails (Tables VIII and IX). With loners, whose trails are easiest to interpret, the investigations discovered a minimum of 0 . 9 scent-marks per km. RLU Characteristics RLU targets were primarily conspicuous vertical objects such as vegetation or snowbanks . RLU's had significantly less urine and significantly less variability in estimated volume 100

80

60

U 0

40

20

I I t I 3 4 5 2 Duration of pair-bond (months)

Fig . 4. Relationship between the percentage of total RLU's involved in double-marks and the duration of the pair-bond in newly formed pairs (r2 = 0 . 96, P < 0 .01) . Includes unpublished data from R . Peters.



'755

ROTHMAN & MECH : WOLF SCENT-MARKING

after the breeding season (Peters & Mech 1975 and Fig . 1). In our captive packs, alpha males RLU'd more often outside the breeding season than did alpha females . The captive females during this period sometimes RLU'd, but usually they SQU'd or urinated with a flexed leg, which seemed to be a low-intensity RLU . Captive alpha female No . 3 was not observed RLU'ing from mid-August to mid-November . On 15 November 1976, she urinated both with a flexedleg and raised-leg, and all of the subsequent urinations observed until her death in February 1977 involved leg lifting to some degree (J . M . Packard, personal communication) . Three observations of wild wolves show that alpha females may at least flexed-leg urinate, if not RLU, outside the breeding season : (1) wolf 2455 on 7 June (S . H . Fritts, personal communication), (2) male 376's mate of less than 6 weeks on 12 July (S . H. Fritts, personal communication), and (3) wolf 2407 on 6 August (Mech, unpublished) .

(X = 2 . 80 cm 3 ± 1'09 SD, n = 29) than did SQU's (If = 6 .19 cm 3 ± 3 . 59 SD, n = 8) . Six

RLU's that we visited weekly during winter 1975 to 1976 were all still visible and odoriferous after six weeks. Both male and female wolves may RLU at any time of year, although the frequency of RLU'ing increases during courtship and again Table V. Periods of Apparent Proestral Bleeding in Wild Wolves, as Detected In Urine Marks, 1976 Minimum periods* of vaginal bleeding Wolf No .

Visible in mark

Female 353t

Detected by urinalysis$ 4-24 Jan . 1976

-

Pair 5139

12-21 Feb .

9 Jan . to 21 Feb .

Pair 5071

13-24 Feb.

20 Jan . to 13 Feb .

*Insufficient samples were obtained outside these periods, so the dates do not necessarily represent the entire period when scent marks contain blood . t Was intermittently with a male during this period . +Urine in snow was collected and analysed by Labstix Reagent Strips (Ames Co ., Elkhart, Ind. 46514 ; mention of brand name does not imply endorsement by U .S . Government) .

Discussion The present study sheds considerable light on the role of scent-marking in the transition between lone-wolf nomadism and pack territory establishment . Furthermore this study strongly

Table VI. Summary of Marking and Investigation Data from Captive South Pack, between August and October 1976 during 20 h of Observation Number Wolf

RLU

Alpha male No . 1

SQU

SCT

SCR

INV

46

2

13

15

57

Alpha female No . 3

0

45

20

0

53

Pups (4)

0

36

26

4

78

*RLU = Raised Leg Urination ; SQU = Squat Urination ; SCT = Scats ; SCR = Scratches ; INV = Investigations . Table VII. Summary of Alpha Pair Double-Marking and Investigation Data from `South Pack' between August and October 1976 during 20 h of Observation* Alpha male No . No. RLU's involved in Total double marks 23

Double Single marks RLU's 29

17

Alpha female No . 3

I

No . investigations of Double Single marks RLU's 21

*RLU's by Male No . I and SQU's by female No . 3 .

9

Single SQU's 35

No . SQU's involved in Double Single marks SQU's 26

19

No . investigations of Double Single Marks RLU's 19

7

Single SQU's 9



ANIMAL BEHAVIOUR, 27, 3

756

suggests that a significant function of scentmarking is pair-bond formation and maintenance . Lone wolves strive to maintain a low profile while travelling . They respond significantly less to recorded howls than do packs (Harrington & Mech in press), and they do not ordinarily scent-mark (Table II). However, lone wolves do have a high investigation rate that would result in locating scent-marks (Table VIII) . The rates of investigation by loners (Table VIII) compare favourably with rates of marking by packs and pairs (Table II, and Peters & Mech 1975), so it is reasonable to assume that loners detect most of a resident pack's sign along its route . Although scent-marking probably does not actually create an impregnable barrier, it no doubt reduces the likelihood of a lone wolf encountering a resident pack . It is easy to see how `reading' of scent-marks might direct lone wolves into unoccupied areas where the likelihood of finding a mate and establishing a territory would be enhanced . One

lone wolf observed from an aircraft `cowered and showed signs of anxiety' after investigating the scent-marks of a resident pack (Jordan et al . 1967). Another female, 5430, while still a loner, showed a more dramatic response . During early winter 1975 to 1976, she was travelling along a frozen river, while about 40 m away, a resident pack slept in the woods . Wolf 5430 stopped, lifted her head as if sniffing the air, and then suddenly ran off . Apparently she had detected the scent or marks of the pack. The next day she was located 22 km to the southwest, where within four weeks she found a mate and territory . In a saturated population, however, it is not always that easy for a loner to find a mate and vacant territory . Wolf 2473, for example, remained alone from 20 October 1972, when she was radio-tagged, until about 10 November 1973, when she began using an area that became her territory . By 20 December 1973, the first time 2473 was seen after settling in the new area, she had a mate . Apparently several vacant

Table VIII. Olfactory Investigations by Single Wolves Trail junctions Wolf

Dist . (km) tracked

No . passed

No . investigated

No . of investigations elsewhere

Investigations per km

No . marks found

5131 5190* 5429* 353 5421

3 .6 1.6 02 5 .8 4.6

9 2 1 26 14

0 0 0 10 4

9 0 1 28 29

2.5 0 5.0 4 .8 6.3

5 0 0 6 3

Total

15 . 8

52

14

67

3.7

14

*Not true lone wolves. See Table I.

Table IX. Olfactory Investigations by Newly Formed Pairs of Wolves Investigations per km

Trail junctions Dist . (km) tracked

No. passed

No . investigated (with or without RLU's*)

No. marked with RLU

5430 353 (1976) 5139 5071 & 5401

5.1 0.8 5.6 19 . 7

8 7 15 25

7 5 9 20

7 4 7 18

4.8 2.6 3 .5 1 .7

9 .2 5 .7 5.1 3 .5

Total

31 . 2

55

41

36

3-2(l)

5 .9 (X)

Wolf

*RLU = Raised Leg Urination .

Rate excluding marking

Total rate (RLU and investigations)



ROTHMAN & MECH : WOLF SCENT-MARKING

areas are checked periodically, presumably those not marked recently by resident packs, until a potential mate is found in one of them . Once two individuals meet, however, a successful pair-bond is not necessarily assured . In most carnivores that pair-bond, lengthy courtship occurs, most likely involving subtle behavioural cues and other signals (Ewer 1973) . Furthermore, individual preferences are well-known in other canids (LeBoeuf 1967 ; Beach 1970 ; Beach & Merari 1970) . Because of the close correlation between RLU'ing and early stages of pairing and because lone wolves do not usually RLU, RLU'ing may be critically related to courtship and pairbonding . Pair-bonding has not been defined in wolves, but we consider it to consist of behavioural interaction between male and female resulting in mutual sexual attraction and attachment lasting at least throughout the gestation period and the raising of any pups born . During courtship, social stimulation, especially dominance-related behaviour, is intensified (Ginsburg 1965) . Our newly formed pairs marked at their highest rates during their first few weeks together (Fig. 2) . In cape hunting dogs (Lycaon pictus), marking was observed 90 min after first encounter (Frame & Frame 1976) . Increased rates of marking around the breeding season have been established clearly in deer (Odocoileus hemionus) Miiller-Schwarze 1972), mongooses (Helogale parvula) (Rasa 1973), and various canids (Kleiman 1966 ; van Lawick-Goodall 1971 ; Golani & Mendelssohn 1971 ; Beach 1974 ; Bekoff & Diamond 1976) . The above observations, along with the many reports of androgen and oestrogen control of scent-marking in gerbils and dogs (Yahr & Thiessen 1975 and refs . therein ; Beach 1974), strongly suggest that hormonal changes due to the social stimulation of courtship are responsible for the onset and frequency of scentmarking. The absence of leg-lifting by lone wolves and by subordinates of a pack and the seasonal differences in frequency of leg-lifting by alpha females might be attributed to differences in hormone levels, but evidence for this is lacking . Leg lifting by females preceding and during the breeding season has also been documented for jackals (Canis aureus) (Golani & Mendelssohn 1971) and coyotes (Canis latrans) (Bekoff & Diamond 1976) . Several studies of a variety of mammals, however, link sex hormones and gonadotropins to the regulation of social status

757

and sexual behaviour, including scent-marking (Lincoln et al . 1972 for red deer ; Rosenblatt & Aronson 1958 for cats ; Rose et al . 1971 for primates ; Clegg et al . 1969 for sheep ; Yahr & Thiessen 1972 for rodents) . Thus it is reasonable to postulate that differences in the levels of certain hormones exist between wolves of different social status and that such differences help regulate scent-marking . However, factors other than cues involved in pair-formation may elicit scent-marking and scent-discharge, presumably by stimulating production of the appropriate steroid hormone or pituitary gonadotropins : change in social rank (Zimen 1975), presence of predators or unusual disturbances (Mykytowycz 1970), agonistic encounters (Schaller 1972 ; Roche 1973 ; Kleiman 1974), and fright or sudden arousal (Ewer 1973) . Thus, adrenal stimulation from sudden arousal may explain our only observation of a lone wolf urinating with a RLU posture four times during the same incident (Results) . It is unknown whether RLU and SQU marks differ chemically . However, endocrine differences associated with different social status may be manifested by the presence, absence, or amount of various metabolites in the urine . Mammals can detect individual differences in scent-marks (Kalmus 1955 ; Bowers & Alexander 1967 ; Gorman 1976) and can detect the reproductive condition and sex of the marker (Beach & Gilmore 1949 ; Brownlee et al . 1969 ; Dunbar 1977) . Furthermore, a compound present in the urine marks of male, but not female, red foxes (Vulpes vulpes) was recently identified (Jorgenson et al . 1978) . The Double-Mark and its Significance To maximize reproductive success a courting pair must be synchronized both physiologically and behaviourally to assure successful fertilization . Hediger (1965) emphasized the importance of synchronization in European hamsters (Cricetus frumentarius), in which either partner may kill the other if not sexually synchronized during mating . We propose that the behavioural and physiological synchronization of wolf pairs is accomplished via the visual and olfactory stimulus of the double-mark . Double-marking has also been referred to as `simultaneous' or 'alternatemarking' in other canids, but we prefer the term `double-marking' because it describes the result of the behaviour rather than the sequence, which is highly variable among canids . Although



758

ANIMAL BEHAVIOUR, 27, 3

Schenkel (1947) proposed several similar pairrelated functions of marking in wolves, his reference to `urine ceremonies' neglected any mention of double-marking by courting individuals. Double-marking has been described as part of courtship in other canids, but without reference to possible function : in dogs (Fox & Bekoff 1975 ; Bekoff, in press), golden jackals Golani & Mendelssohn 1971 ; Golani & Keller 1975), coyotes (Bueler 1973 ; Bekoff & Diamond 1976), Cape hunting dogs (van Lawick-Goodall 1971 ; Frame & Frame 1976), raccoon dogs (Nyctereutes procyonoides), and bat-eared foxes (Otocyon megalotis) (Kleiman 1968) . In both wild dogs and golden jackals, double-marking occurred almost immediately after members of the pair first met (Golani & Keller 1975 ; Frame & Frame 1976). Four characteristics of the double-mark convince us of its importance in pair-formation and courtship success : (1) it apparently is absent in pairs that later fail to mate, (2) it is associated with high rates of mutual investigation ; (3) its frequency is maximal immediately after pairing, and eventually decreases to a base rate ; and (4) it is performed almost exclusively by the high-ranking, breeding pair . High-ranking wolves are the breeders in a pack . Thus if the double-mark involves information exchange necessary for courtship and mating, then such behaviour and information would not be important in subordinates, and they would not be expected to double-mark . Furthermore, only a potentially breeding pair, free of the social restraints and inhibitions that affect subordinates, would be capable of producing a doubleRLU . L . H . & G . W . Frame (personal communication) observed one case of doublemarking by a subordinate pair of Cape hunting dogs . The dominant female arrived shortly after the mark was made and urine-marked over the double-mark, after which the subordinate pair was never seen double-marking again . The apparent change in degree and frequency of leg-lifting in female wolves as the courtship and breeding seasons approach (see 'RLU Characteristics)' may be facilitated by some synergistic effects of double-marking . The significance of the inverse relationship between frequency of double-RLU's and length of the pair-bond (Fig . 4) is unclear . However, in certain birds, courtship duration and display frequency between members of previously established pairs are lower than in new pairs

(Coulson 1966 ; Erickson & Morris 1972) . These studies suggest decreased courtship intensity with familiarity . The paucity of such information in mammals points out the need for further studies of the role of experience on courtship duration and mating success . For scent-marking to be effective in courtship and pair-bonding, conspecifics must perceive the marks and behave appropriately . Sexual preferences for urine of the opposite sex, preference for urine from oestrous females over non-oestrous ones, and a change in behaviour upon sniffing urine have all been documented in canids (Beach & Gilmore 1949 ; Doty & Dunbar 1974 ; Gier 1975 ; Anisko 1976) . In wolves, all pack members investigate scent-marks, but most investigations are by the alpha pair that produced them (Tables VI, VII) . Furthermore, lone wolves of both sexes, and newly formed pairs, probably spend substantial time during their travels investigating scent-marks, for their investigation rates are high (Tables VIII, IX) . In packs, subordinate wolves have at least as good an opportunity as the alpha pair to inspect the pair's marks when the group travels together . Over 90 % of the double-marks of captive alpha pairs were investigated by other pack members soon after they were produced . Because neither loners nor pack subordinates perform RLU's, and neither possess mates, some sort of social intimidation or reproductive suppression could be mediated through olfactory cues. That olfactory signals in urine can exert such an influence on mammalian reproduction has been well-documented (Whitten 1956 ; Parkes & Bruce 1961 ; Bronson 1974 ; Lombardi & Vandenbergh 1977) . The attractive properties of urine from members of the opposite sex make it likely that members of a breeding pair will investigate each other's marks, as our studies of captive wolves indicate they do (Table VII) . Undoubtedly, these olfactory investigations assist in the essential synchronization of the breeding pair's reproductive cycles . This would explain the intensive interest that pair members exhibit for their own marks (Table VIII), which would be necessary to determine whether the partner had marked over it . Attempts at isolation of a priming pheromone in canid urine are currently being undertaken (W . Whitten, personal communication) .



ROTHMAN & MECH : WOLF SCENT-MARKING

A further function of double-marking might be to indicate to loners whether or not a mated pair exists in a territory . The junior author observed a case in which an alpha female of a pack lacking other adult females was killed . The alpha male continued to RLU, and the dead wolf's place was eventually filled by a female loner. The loner may have detected the absence of fresh double-marks and thus determined that no other female was present in the pack. Instead of fleeing from the vicinity of the pack, as a lone wolf usually would, this loner travelled parallel to the pack until she was eventually accepted as the alpha female . The results of the present study, combined with those of Peters & Mech (1975), indicate that the urine-marking system in wolves serves a dual function : (1) reproductive synchronization, and (2) territory advertisement and enforcement. The need for a complex, unambiguous signalling system is clear in species where individuals change their social condition from solitary to group living (Kleiman 1967 ; Kruuk 1975) . Because RLU-marking first appears in newly formed pairs during a period of social transition, it seemingly would qualify as such a signal . Acknowledgments We thank the Wilkie Foundation, U .S . Fish and Wildlife Service, U .S .D.A . North Central Forest Experiment Station, and the Department of Ecology and Behavioural Biology of the University of Minnesota for financial and logistic support . Grateful appreciation is also extended to the following people for assistance in ground-tracking wolves : J . Renneberg, S . Knick, W . Paul, M . Korb, J . M . Packard, D . Bruggers, and S . Lampman . E. C . Birney, F . McKinney, A . Pace, C . K . Snowdon, R . Lillehei, R . Timm, J . Colin, and S . H. Fritts reviewed earlier drafts of this article, and N. Holschuh provided advice on statistical analysis . REFERENCES Anisko, J . 1976 . Communication by chemical signals in canids . In : Mammalian Olfaction, Reproductive Processes, and Behavior (Ed . by R. Doty), pp . 283-293 . New York : Academic Press . Beach, F. 1970. Coital behavior in dogs . VIII . Social affinity, dominance and sexual preference in the bitch . Behaviour, 36, 131-147 . Beach, F . 1974. Effects of gonadal hormones on urinary behavior in dogs . Physiol . Behav., 12, 1005-1013 . Beach, F . & Gilmore, R . W. 1949. Response of male dogs to urine from females in heat . J. Mammal., 30, 391-392 .

759

Beach, F. & Merari, A . 1970 . Coital behavior in dogs . V . Effects of estrogen and progesterone on mating and other forms of social behavior in dogs . Psych . Monogr ., 70, 1-32 . Bekoff, M . In press . Scent-marking by free-ranging dogs ; olfactory and visual components . Biol. Behav . Bekoff, M . & Diamond, J . 1976. Precopulatory and copulatory behavior in coyotes . J. Mammal., 57, 372-375 . Bowers, J . M . & Alexander, B . K. 1967 . Mice : individual recognition by olfactory cues . Science, N. Y., 158, 1208-1210. Bronson, F. H . 1974. Pheromonal influences on reproductive activities in rodents . In : Pheromones (Ed . by M . C . Birch), pp. 344-365 . New York : American Elsevier. Brownlee, R . G ., Silverstein, R. M ., Muller-Schwarze, D . & Singer, A . G . 1969 . Isolation, identification and function of the chief component of the male tarsal scent in black-tailed deer . Nature, Lond., 221, 284-285 . Bueler, L. 1973 . Wild Dogs of the World. New York : Stein and Day. Clegg, M . T., Beamer, W . & Bermant, G . 1969 . Copulatory behaviour of the ram (Ovis aries) : effects of pre- and post-pubertive castration and androgen replacement therapy. Anim. Behav ., 17, 712-717 . Coulson, J. C. 1966 . The influence of the pair-bond and age on the breeding biology of the Kittiwake gull (Rissa tridactyla) . J. Anim . Ecol., 35, 269-279 . Doty, R . L. & Dunbar, I . 1974. Attraction of beagles to conspecific urine, vaginal and anal sac secretion odors . Physiol. Behav., 12, 825-833 . Dunbar, I . F . 1977. Olfactory preferences in dogs : the response of male and female beagles to conspecific odor. Behav . Biol ., 20, 471-481 . Erickson, C . & Morris, R . 1972 . Effects of mate familiarity on the courtship and reproductive success of the ring dove (Streptopelia risoria) . Anim . Behav., 20, 341-344. Ewer, R . F . 1973 . The Carnivores . Ithaca, New York : Cornell University Press . Fox, M . W. & Bekoff, M . 1975 . The behaviour of dogs . In : The Behaviour of Domestic Animals (Ed . by E . S . E . Hafez), pp. 370-409 . London : Balliere Tindall . Frame, L . H . & Frame, G. W . 1976 . Female African wild dogs emigrate . Nature, Lond., 263, 227-229 . Gier, H . T. 1975 . Ecology and social behaviour of the coyote. In : The Wild Canids (Ed. by M . W. Fox), pp . 247-262. Princeton, New Jersey : Van Nostrand-Reinhold. Ginsburg, B . 1965 . Coaction of genetical and nongenetical factors influencing sexual behavior . In : Sex and Behaviour (Ed . by F. Beach), pp . 5375 . New York : Wiley. Golani, I . & Keller, A . 1975 . A longitudinal field study of the behavior of a pair of golden jackals . In : The Wild Canids (Ed . by M . W. Fox), pp . 336362. Princeton, New Jersey : Van NostrandReinhold . Golani, 1. & Mendelssohn, H. 1971 . Sequences of precopulatory behavior of the jackal (Canis aureus L .) . Behaviour, 38, 169-192. Gorman, M . L . 1976. A mechanism for individual recognition by odor in Herpestes aurapunctatus (Carnivora : Viverridae) . Anim . Behav., 24, 141-145 .

7 60

ANIMAL BEHAVIOUR, 27, 3

Harrington, F . H . & Mech, L. D . In press . Wolf howling and its role in territory maintenance . Behaviour. Hediger, H . 1965 . Environmental factors influencing the reproduction of zoo animals . In : Sex and Behavior (Ed . by F. Beach,) pp . 319-354 . New York : Wiley . Jordan, P ., Shelton, P . & Allen, D . L . 1967 . Numbers, turnover, and social structure of the Isle Royale wolf population . Am. Zool., 7, 233-252 . Jorgenson, J . W., Novotny, M., Carmack, M ., Copland, G. B., Wilson, S . R ., Katona, S . & Whitten, W. K . 1978 . Chemical scent constituents in the urine of the red fox (Vulpes vulpes L .) during the winter season . Science, N. Y., 199, 796-798 . Kalmus, H. 1955 . The discrimination by the nose of the dog of individual odors and in particular the odor of twins . Br. J. Anim. Behav ., 3, 25-31 . Kleiman, D . 1966. Scent-marking in the Canidae . Symp . Zool. Soc. Lond., 18, 166-177. Kleiman, D . 1967 . Some aspects of social behavior in the Canidae . Am. Zool., 7, 365-372 . Kleiman, D . 1968 . Reproduction in the Canidae. Int . Zoo Yearbook, 8, 107 . Kleiman, D . 1974. Scent marking in the Binturong (Arctictis binturong) . J. Mammal., 55, 224-227 . Kruuk, H . 1975 . Functional aspects of social hunting in carnivores . In : Function and Evolution in Behaviour (Ed . by G . Baerends, C. Beer & A . Manning), pp . 119-141 . Oxford : Clarendon Press . van Lawick-Goodall, H. & J. 1971 . Innocent Killers . New York : Ballantine Books. LeBoeuf, B . 1967 . Interindividual associations in dogs . Behaviour, 29, 268-295. Lincoln, G . A ., Guiness, F. & Short, R . V . 1972 . The way in which testosterone controls the social and sexual behavior of the red deer stag (Cervus elaphus). Horm . Behav ., 3, 275-396 . Lombardi, J. R . & Vandenbergh, J . 1977 . Pheromonally induced sexual maturation in females : regulation by the social environment of the male . Science, N.Y., 196, 545-546 . Mech, L . D . 1970. The Wolf. Garden City, New York : Nat . Hist . Press . Mech, L . D . 1972. Spacing and possible mechanisms of population regulation in wolves . Am . Zool., 12,642 . Mech, L. D . 1973 . Wolf Numbers in the Superior National Forest of Minnesota. U.S .D.A . Forest Service Research Paper NC-97 . Mech, L. D. 1974. Current techniques in the study of elusive wilderness carnivores . Proc . Xlth Int. Cong. Game Biol ., 11, 315-322. Mech, L . D . 1977. Productivity, mortality, and population trends in wolves from northeastern Minnesota. J. Mammal., 58, 559-574. Mech, L. D . In press . A summary of wolf studies in northeastern Minnesota. Proc . 1978 Wildlife Symp., Edinburgh University. Mech, L. D. & Frenzel, L . D ., Jr. 1971 . Ecological Studies of the Timber Wolf in Northeastern Minnesota . U.S .D .A . Forest Service Research Report NC-52 .

Mech, L. D . & Knick, S . T. 1978 . Sleeping distance in wolf pairs in relation to the breeding season . Behav . Biol., 23, 521-525 . Mtiller-Schwarze, D . 1972 . Social significance of forehead rubbing in black-tailed deer (Odocoileus hemionus columbianus) . Anim . Behav ., 20, 788797 . Mykytowycz, R . 1970. The role of skin glands in mammalian communication . In : Advances in Chemoreception, Vol . 1 : Communication by Chemical Signals (Ed . by J . W . Johnston, Jr, D . G . Moulton & A . Turk), pp. 327-361 . New York : AppletonCentury-Crofts. Odum, E . P . 1971 . Fundamentals of Ecology . Philadelphia : W . B . Saunders . Ohmann, L. F . & Ream, R . R . 1971 . Wilderness Ecology : Virgin Plant Communities of the Boundary Waters Canoe Area. U .S .D .A . Forest Service Research Paper NC-63 . Parkes, A . S . & Bruce, H . M . 1961 . Olfactory stimuli in mammalian reproduction . Science, N.Y, 134, 1049-1054 . Peters, R . & Mech, L . D . 1975 . Scent-marking in wolves . Am . Scient ., 63, 628-637 . Rasa, O . A . E . 1973 . Marking behavior and its social significance in the African dwarf mongoose (Helogale undulata rufula) . Z. Tierpsychol ., 32, 293-318 . Roche, F . 1973 . A wolf by any other name . Defenders of Wildlife News, 48, 196-198 . Rose, R . M ., Holaday, J. W. & Bernstein, I . S . 1971 . Plasma testosterone, dominance rank and aggressive behavior in male rhesus monkeys . Nature, Lond., 231, 366-368 . Rosenblatt, J . S . & Aronson, L. 1958 . The decline of sexual behavior in male cats after castration with special reference to the role of prior sexual experience. Behaviour, 12, 285-338 . Schaller, G . 1972 . The Serengeti Lion . Chicago : University of Chicago Press . Schenkel, R . 1947 . Expression studies on wolves . Behaviour, 1, 81-129 . Seal, U. S ., Plotka, E ., Packard, J . M . & Mech, L . D. In press. Endocrine correlates of reproduction in the female wolf. Biol. Reprod. Van Ballenberghe, V . & Erickson, A . W . 1973 . A wolf pack kills another wolf . Am . Midl . Nat ., 90, 490-493 Whitten, W. K. 1956 . Modifications of the estrous cycle of the mouse by external stimuli associated with the male. J. Endocrin ., 13, 399-404 . Yahr, P . & Thiessen, D . D. 1972. Steroid regulation of territorial scent-marking in the Mongolian gerbil (M. unguiculatus). Horm . Behav ., 3, 359-368 . Yahr, P . & Thiessen, D . D . 1975 . Estrogen control of scent-marking in female Mongolian gerbils (Meriones unguiculatus) . Behav . Biol., 13, 95-101 . Young, S . P . 1944 . The Wolves of North America, part I . Washington, D .C . : American Wildlife Institute. Zimen, E . 1975 . Social dynamics of a wolf pack . In : The Wild Canids (Ed . by W . M. Fox), pp . 336-362 . Princeton, New Jersey : Van Nostrand-Reinhold . (Received 1 February 1978 ; revised 16 November 1978 ; MS . number: A2135)