Am. Midl. Nat. 139:275–281

Behaviors of Bobcats Preying on White-tailed Deer in the Everglades

RONALD F. LABISKY1 AND MARGARET C. BOULAY2

Department of Wildlife Ecology and Conservation, University of Florida, Gainesville 32611
ABSTRACT.—Predatory behaviors of bobcats (Lynx rufus) that preyed on 39 radio-instrumented white-tailed deer (Odocoileus virginanus) in the Everglades during a 3-yr study, 1 April 1989–31 March 1992, are described and compared with those of other felids. Bobcats killed 33 fawns and six adults by administering $one bite to the neck and throat region. The maximum prey : predator weight ratio was 8:1. Twelve (31%) of 39 kills were dragged 2–10 m to concealment cover before being eaten. Twelve (71%) of 17 carcasses that were not dragged from the kill site exhibited a characteristic death form in that the head on each was twisted backwards (throat dorsal) and positioned diagonally under the shoulder. Feeding was initiated on large muscle masses, predominantly on the hindquarters. Bobcats eviscerated 29 (83%) of 35 carcasses, severed $ one fore- or hind-limbs from 18 (55%) of 33 kills, and
plucked hair from 13 (33%) of 39 carcasses. Bobcats partially or completely covered 17 (52%) of 33 carcasses with plant litter. Thus, bobcats preying on deer in the Everglades displayed notable differences in eviscerating, feeding, and covering behaviors.

INTRODUCTION

Throughout their range, bobcats (Lynx rufus) prey on small to medium-sized species, principally rodents and lagomorphs (Fritts and Sealander, 1978; Kitchings and Story, 1979; Fox and Fox, 1982; Litvaitis et al., 1986; Maehr and Brady, 1986; Wassmer et al., 1988). Bobcats also kill large prey, such as white-tailed deer (Odocoileus virginianus)during winter (Litvaitis et al., 1986), or scavenge on large prey that die from other causes (Pollack, 1951;
Fritts and Sealander, 1978; Kitchings and Story, 1979; Fox and Fox, 1982). In some areas, bobcats prey extensively on fawns of white-tailed and mule deer (O. hemionus) (Garner et al., 1976; Epstein et al., 1983). A 3-yr study, 1 April 1989–31 March 1992, of survival of radio-instrumented white-tailed deer fawns and adults in the Florida Everglades revealed that bobcat predation accounted for $60% of 52 fawn deaths (Boulay, 1992), and $17% of 36 adult deaths (Labisky et al., 1995). The magnitude of this predator-prey interaction provided a unique opportunity to elucidate the predatory behaviors of bobcats. Accordingly, the objectives of this paper were to describe and quantify the killing, feeding and covering behaviors associated with 32 fawn and six adult white-tailed deer killed by bobcats in the Everglades, and to compare these behaviors with those of other felids.

STUDY AREA

The study area encompassed approximately 200 km2 of the wet prairie/tree island community of Big Cypress National Preserve and Everglades National Park in southern Florida. This region is characterized by a subtropical climate, with distinct dry/winter and wet/ summer seasons. Mean annual temperature is 23 C; mean monthly temperatures range from
14 C in February to 28 C in August (Duever et al., 1986). Mean annual precipitation is 136 1 Corresponding author
2 Present address: Oregon Department of Fish and Wildlife, Oakridge, Oregon 97463 276 THE AMERICAN MIDLAND NATURALIST 139(2) cm, of which two-thirds falls during April–October, resulting in seasonal flooding (Duever et al., 1986). Topographic relief is minimal. The habitat consisted primarily of wet prairie (93%) that was interspersed with slightly
elevated (1 m) hardwood tree islands (7%) (Duever et al., 1986; Miller, 1993). Common species of the wet prairie included sawgrass (Cladium jamaicensis), maidencane (Panicum hemitomon), sand cordgrass (Spartina bakeri), muhly grass (Muhlenbergia filipes) and swamp lily (Crinum americanum). Tree islands were characterized by both temperate and tropical hardwoods, including red bay (Persea borbonia), sweet bay (Magnolia virginiana), wax myrtle (Myrica cerifera), cabbage palm (Sabal palmetto), oaks (Quercus spp.), gumbo limbo (Bursera simaruba) and cocoplum (Chrysobalanus icaco).
Deer density on the study site was relatively low, ranging from 3.5–5.0 deer/km2 during study period (Labisky et al., 1995). The mean fawning date was 22 February (Boulay, 1992). The density of bobcats on the study site was unknown, but considered substantial due to frequent daytime sightings and the high rate of predation on deer (Labisky et al., 1995).

METHODS

Deer were pursued by helicopter and captured by netgun (Barrett et al., 1982) or by hand (neonatal fawns) during 1989, 1990 and 1991. Sex, age (fawns: Haugen and Speake, 1958; adults: Severinghaus, 1949), morphometics and physical condition (Stockle et al., 1978) were recorded for each deer, which also was marked with a numbered No. 49 monel
tag in each ear and a radio-transmitter collar (Wildlife Materials, Inc., Carbondale, Illinois). Transmitters emitted resting (13 pulse), activity (23), and mortality (43) signal modes. The mortality mode was activated after 2–5 h collar inactivity. Individual signals were monitored for mortality mode four of every five calendar days by aerial telemetry.
Potential predators of deer included the Florida panther (Puma concolor coryi), bobcat, black bear (Ursus americanus), gray fox (Urocyon cinereoargenteus) and American alligator (Alligator mississippiensis). Carcasses were examined as soon as possible, usually 1–3 days postmortem, and field necropsies were performed (Nettles, 1981; Davidson and Nettles, 1988). The carcass and surrounding habitat were photographed and examined for signs of predation (Wade and Bowns, 1984). Predation was considered a possible cause of death when the carcass exhibited evidence of trauma. The head, throat and neck regions of each carcass were skinned and examined for puncture wounds, subcutaneous hemorrhaging and tissue damage (Nettles, 1981; Davidson and Nettles, 1988). Feeding by the predator was
differentiated from scavenging by the freshness of the carcass, relative amount and pattern of consumption and presence of hemorrhaging (Cook et al., 1971; Hawthorne, 1980; Bartush and Lewis, 1981). The dominant scavengers on the study area were the turkey vulture (Cathartes aura) and black vulture (Coragyps atratus). Felids were considered as responsible predators if the head, neck and throat region revealed trauma from bites; if the carcass had been dragged, eviscerated or covered; if deer hair had been plucked; or if signs such as mounds, scrapes, tracks and scats were present (Robinette et al., 1959; Hawthorne, 1980; Wade and Bowns, 1984). Distance between and diameter of tooth marks, location and number of bites, type of bone damage, amount of consumption in relation to elapsed time and size of tracks and scrapes were used to differentiate predation by panthers and bobcats (Hawthorne, 1980; Wade and Bowns, 1984). Two terms common in felid behavior, covering and caching, warrant explanation. Covering
of the prey carcass by the predator before leaving the kill is a behavior that generally is considered an attempt to conceal the carcass from scavengers, whereas caching usually refers to the storing of surplus carcasses by a predator for later consumption (Kitchener, 1991). Although carcasses that were covered at the kill site by bobcats in this study may
1998 LABISKY & BOULAY: BOBCATS AS PREDATORS 277 have been cached, particularly inasmuch as they were often fed upon during later visits, we have elected to refer to this behavior only as ‘‘covering.’’

RESULTS

Thirty-nine deer [33 fawns (,1 yr in age): 13 females, 20 males; 6 adults ($2 yr): 5 females, 1 male) were killed by bobcats; bobcats were observed at five kills. The mean age of the 32 fawns at death was 4.4 6 2.4 SD (range 5 1.2–11.5) mo; carcass weights of fawns varied from 6 to 25 kg. The weight at death of the five adult females ranged from approximately 30 to 42 kg, and that of the adult male, $48 kg. Sixteen (41%) of the 39 carcasses were examined within 24 h of death, 13 (33%) between 24 and 48 h, and 10 (26%) between 48 and 72 h. Bobcats killed both fawns and adults with one bite to the throat and neck; however, no broken necks were observed. Canine punctures, and resultant internal hemorrhaging, were verified on the necks of 20 (51%) of the 39 kills; the trachea also was punctured on five of the 20 kills. The method of killing was not verified on the other 19 kills because the necks had been consumed by the bobcat or by scavengers. Five deer, including three fawns and two pregnant females, were attacked and killed while they were bedded. Field evidence indicated the adult male was attacked by a bobcat while it was traversing a complex of jagged pinnacle rocks; the distance from ambush to kill-site was 30 m. Twelve (31%) of the 39 deer (10 fawns, two adults) killed by bobcats were dragged 2–10 m to concealment cover before being fed upon or covered; all other kills were fed upon at the kill site. Notably, the carcasses of 12 (71%) of 17 deer that were not moved from the kill site displayed a characteristic death form with respect to the posture of the head, which was twisted backwards (throat dorsal) and positioned partially under the shoulder of the deer.

The pattern of feeding on the carcass by bobcats was inferred from the amount and location of consumed meat, including organs. Large muscle groups generally were consumed first. Of 25 carcasses from which initial feeding behavior by bobcats was determined, 13 (52%) revealed feeding principally on the hindquarters, five (20%) on both front and hindquarters, and two (8%) principally on the frontquarters; five (20%) carcasses, all fawns, exhibited a whole-carcass feeding pattern and were almost totally consumed. If the carcass was eviscerated, the heart and lungs frequently were consumed. Two of the five adult females killed by bobcats were approaching term pregnancy (one possibly in the process of birthing); bobcats initially consumed the fetus and a portion of the hindquarters in both
instances. Notably, $one fore- or hind-limbs were severed from the body by the bobcats on 18 (55%) of 33 kills; the limbs often were dragged 2–10 m from the carcass to be fed upon, but were covered by plant debris on only four occasions. Bobcats eviscerated 29 (83%) of 35 carcasses for which data were available. Some of the body organs, especially the rumen, often were dragged 1–10 m from the carcasses and placed in a mound, but were covered or buried in only four instances. Plucking of body hair was noted on 13 (33%) of the 39 carcasses. Plucked hair often was incorporated with the covering of the carcass, or portions of the carcass, with vegetative litter.

Bobcats covered parts or all of 17 (52%) of 33 deer carcasses, usually with a combination of live and dead plant material available at the kill-site; the degree of covering ranged from partial to complete. Three fawn carcasses were deposited intact, without being covered, in tussocks of sawgrass. Bobcats displayed behavioral differences in feeding on deer that were scavenged in contrast to those than were preyed upon. Consumption of four scavenged deer was restricted 278 THE AMERICAN MIDLAND NATURALIST 139(2) to the hindquarters, and only that portion of the carcass was covered. None of the scavenged deer was eviscerated, delimbed, plucked, or dragged from the death site.

DISCUSSION

The hunting behavior of the bobcat, principally a solitary hunter, consists of three phases: stalking the prey, usually from the concealment of cover; using short bursts of speed to reach the prey; and attacking the prey with a pounce or jump (McCord and Cordoza, 1982; Kruuk, 1986). When bobcats have killed adult deer, they reportedly stalked and ambushed the animals while they were bedded (Marston, 1942; McCord, 1974; McCord and Cordoza, 1982). Similarly, bobcats in the Everglades, ambushed and killed five deer in their bedsites, including two (pregnant) adult females. However, bobcats also are capable of ambushing large prey while they are mobile, as was evidenced by the killing of an adult male deer. Felids kill prey by administering a lethal bite, usually on the head or neck of the prey; death is a result of suffocation (collapse of trachea), or severing of the cervical vertebrate or spinal cord (Kruuk, 1986). Attacking the neck region appears to be particularly effective when a felid ambushes prey larger than itself. Bobcats in the Everglades exhibited this behavior as shown by the multiple-bite marks frequently observed on the necks and throats
of large fawns and adult deer. The ratio of prey weight to bobcat weight merits mention. Weights of adult bobcats in
Florida range from 5.7 to 10.2 kg for females and 9.0 to 12.5 kg for males (Progulske, 1982; Wassmer et al., 1988). Thus, the ratio of prey (deer) weight to bobcat weight in the Everglades potentially varied from a minimum of 1:2 (small fawn, large bobcat) to a maximum of 8:1 (adult deer, small bobcat). Comparatively, other solitary hunting felids also display high maximum prey : predator weight ratios, e.g., cougars (Puma concolor), 6.17:1; cheetahs, 4.13:1; tigers (Panthera tigris), 2.78:1; and lynx (Lynx canadensis), 2.25:1 (Packer, 1986). Furthermore, the prey : predator weight ratio for bobcats [8:1 (this study); 7.25:1 (Packer, 1986)] is similar to the reported ratio [7.45:1 (Packer, 1986)] for lions (Panthera leo), which often hunt in groups to facilitate the taking of large prey. Although the capability of the
bobcat to kill prey larger than itself is consistent with the killing capability of other felids, the bobcat appears to be unusually adept in its ability to kill prey species many-fold larger than itself despite the fact that it is a solitary hunter.
A frequent, and previously unreported, characteristic of deer killed by bobcats in this study was that the head was twisted backwards (throat dorsal) and rotated partially under the carcass. Although the process associated with this behavior was not observed in the field, two explanations can be posed. First, Eaton (1974) reported that the cheetah (Acinonyx jubatus) characteristically gripped the upper ventral neck of felled prey, rotated it laterally, and held the bite until the animal was suffocated. Although this method of killing deer by bobcats is plausible, it does not explain how the head was positioned under the body.

Second, the phenomenon could have been the result of the bobcat grasping the dorsally exposed shoulder of the deer after it was felled, and then pulling it forward until it ceased struggling, a behavior observed among felids that take large prey (Leyhausen, 1970). The frequency of bite and claw marks observed on the exposed shoulders of numerous
deer carcasses support this latter contention. Where on the carcass a cat begins feeding tends to be species-specific, e.g., tigers and pumas initially feed on the hindquarters (rump); lions on the viscera; jaguars (Panthera onca) on the forequarters, chest and neck chest; cheetahs on the hindquarters (rump); and lynx, bobcats and ocelots (Leopardus pardalis) on the head (Sunquist, 1981; Kruuk, 1986).

In the Everglades, bobcats began feeding on the large muscle groups of deer, principally on the hindquarters (rump) but occasionally on the shoulders, after which they opened 1998 LABISKY & BOULAY: BOBCATS AS PREDATORS 279 the thoracic cavity and fed on the ribs, heart and lungs. Although the pattern of feeding by bobcats on deer in the Everglades appears as a contradiction to the observation that small cats begin feeding on the head region of prey, most felids that feed on prey larger than themselves often initiate feeding on the viscera or hindquarters (Kitchener, 1991).
Observations from this study revealed that bobcats fed only on the hindquarters of scavenged deer. McCord (1974) observed that bobcats making multiple visits to a carcass fed significantly more on carcasses they had killed (79% of 17 visits) than carrion carcasses (18% of 16 visits). Thus, bobcats may tend to take but a single feeding from carrion due
to opportunism, advanced decomposition of the flesh or decreased water content of the meat.

Bobcats in the Everglades exhibited a strong tendency (82%) to eviscerate the carcasses of the deer they killed. In the gutting process, the rumen often was removed from the visceral cavity, dragged a short distance from the carcass and deposited in a pile, a behavior that parallels that of other felids, e.g., tiger (Sankhala, 1977). Covering of carcasses (or carcass remains) with vegetation has been documented extensively for cougars (Robinette et al., 1959; Beier et al., 1995), but less consistently for other felids, such as tigers (Sunquist, 1981) and bobcats (Marston, 1942; McCord and Cordoza,1982). However, this study revealed that bobcats covered more than half (52%) of the carcasses. Their covering tactic embodied the piling of live and dead vegetation, principally grasses, on the carcasses by raking movements with the front limbs, a behavior similar to that of other felids (Vander Wall, 1990)

In summary, bobcats preying on deer in the Everglades exhibited sterotypical killing behaviors, but exhibited differences in eviscerating, covering, and feeding behaviors. Differences in the latter behaviors appeared individualistic, but may have been driven by the energetic needs of the bobcat as related to reproductive status, i.e., female with kittens, or seasonally fluctuating availability of prey species other than deer.

Acknowledgments.—This research was funded by the National Park Service (Big Cypress National Preserve) and the University of Florida. K. E. Miller, R. A. Sargent, Jr., and J. M. Zultowsky participated in data collection. J. F. Eisenberg, D. Jackson, J. N. Layne and M. E. Sunquist provided comments on the manuscript. This paper is a contribution ( Journal Series No. R-05634) of the Florida AgriculturalExperiment Station, Gainesville.


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SUBMITTED 16 AUGUST 1996 ACCEPTED 28 JULY 1997