In 1989, research was undertaken to investigate the basic ecological role of coyotes in Yellowstone. The park is one of the few places where the natural behavior of coyotes is not strongly influenced by trapping or predator control programs. Here, a unique opportunity existed for scientists to study the social behavior of coyotes and their interactions with prey and other predators, such as bears, mountain lions, and to document their ecology in Yellowstone prior to the proposed return of gray wolves.
Researchers captured and radio-collared coyotes, mainly on Yellowstone's northern range, to study movements and behavior. Males and females were sampled from at least 16 different resident packs. Researchers estimated that 85 to 90% of coyotes on the northern range belong to packs. Average pack size during the winters of 1990-93 ranged from 6.2 to 7.1 animals, typically a dominant, mated alpha-pair and subordinate beta individuals. The betas are pups from previous litters that remain in the area in which they were born. Evidence strongly indicated that coyote territories are traditional, with some coyotes using the same natal dens documented in 1940, when Adolph Murie studied coyote ecology in the Lamar Valley. Wolf extirpation in the first decades of the 20th century probably resulted in high coyote population densities and coyotes at least partially slid into this vacant niche.
Small mammals are an important component of coyotes’ diets. In Yellowstone, such prey include microtines or voles (Microtus spp.), mice (Peromyscus spp.), pocket gophers (Thomomys talpoides), small birds such as grouse, and in spring and summer, Uinta ground squirrels (Spermophilus armatus). In one study (Gese et al. 1996), scientists observed 4,439 predation attempts by coyotes, 35% of which (1,545) were successful. Young, inexperienced coyotes detected and attacked small mammals at a higher rate than did older coyotes. Older animals were more selective, making fewer attempts at small mammal predation, but interestingly, pups and older coyotes captured similar numbers of small mammals per hour. The depth and hardness of snow influenced how well coyotes detected and killed small prey, which was most successful in moist meadows and sagebrush grasslands. The coyotes capturing small mammals consumed 98.6% of their kills, only rarely caching or immediately sharing the prey. However, coyotes often regurgitate their prey to help feed pack members. Alpha males were seen delivering whole prey to their mates during the time of gestation and pup rearing. Alphas, betas, and older pups brought food to the current year’s litter of pups at den sites.
Carrion from winterkilled ungulates (elk, deer, bison, moose, pronghorn, and bighorn sheep), as well as predation on these larger mammals, also provides vital coyote food. Coyotes appeared to affect ungulate numbers in three ways: predation on calves and fawns shortly after birth, predation on "short-yearlings" (animals just shy of one year old) and adults during winter, and indirect impacts from harassment of other predators at ungulate kills. Researchers in Yellowstone and elsewhere have observed both successful and unsuccessful attempts at predation of elk calves and mule deer fawns. Observations of coyotes preying on adult elk and deer are more rare, although Gese and Grothe (1995) observed 9 such winter attempts in the park, 5 of which were successful. In all but one case, the alpha male coyote led the attack. In all cases, the coyotes attacked from the rear and/or the flanks of their prey. Occasionally they also grabbed the neck and head, pulling the animal down to the ground. Successful attacks lasted from 14 minutes to about 21 hours; even unsuccessful ones varied from 2 minutes to more than 8 hours before the coyotes abandoned the effort. Depth of snow affected the likelihood of success, although two or more adult coyotes could kill both calf and adult elk even during deep snow conditions, if the prey were in poor condition. In 3 of the 4 unsuccessful attempts, the intended prey fled into water, and researchers observed several other instances in which coyotes approached prey but did not pursue when the elk or deer entered a river. The researchers noted that some coyote pack members stayed nearby watching while 2 or 3 animals made the kill; in contrast, in other study areas all pack members appear to all be involved in the chase and kill.
Coyotes were also observed harassing both mountain lions and grizzly bears from their kills. And coyotes were sometimes killed by other carnivores, especially mountain lions, and by vehicular collisions. Coyotes are also subject to disease, including several pathogens that are known to kill coyotes in their first 3 months of life. Park coyotes have also shown exposure to canine parvovirus, canine distemper, plague (Yersinia pestis), tularemia, and leptospirosis, but not brucellosis. These diseases may be transmitted to coyotes from other wild canids, or from domestic dogs coming into the park.Post-Wolf Research
In 1995, wolves were returned to Yellowstone. Throughout the restoration project, coyote research has continued, with an eye toward identifying the interactions between coyotes and wolves and on assessing the effects of wolves on coyote populations. During planning and environmental assessment of the effects of wolf restoration, biologists anticipated that coyotes would compete with the larger canid, perhaps resulting in disruption of packs and numerical declines.
Although early in the post-wolf study period, scientists have already observed some changes in the northern range coyote population as a result of restoring the larger canid. Shortly after wolves arrived in Yellowstone, coyote vocalizations increased in and around wolf acclimation pens and territories. During 1995-1997, coyote pack territories shifted and, in some cases, packs disintegrated as a result of one or more of the alpha coyotes was killed. Coyote den sites are more likely to be under rocks or closer to the park roadway¾ perhaps because humans pose less threat to coyotes than do wolves. Coyote pup survival and weight have increased, as has group cohesion among coyotes; this is likely a result of their banding together for protection against wolves. Researchers documented that wolves killed at least 13 adults coyotes in the winter of 1995-1996 and 7 coyotes during 1996-1997. Coyote numbers have declined, although the species is still abundant and well-distributed throughout the park. It is expected that the two species will settle into a pattern of coexistence such as existed prior to the establishment of Yellowstone National Park—a pattern that is newly being discovered by many observers of the ecosystem.Coyote-Human Interactions
Coyotes occasionally lose their wariness of humans and frequent roadsides or developed areas, becoming conditioned to human food by receiving handouts or picking up food scraps. They can quickly learn bad habits like roadside begging behavior. This leads to potential danger for humans and coyotes. Several instances of coyote aggression toward humans have occurred in the park, including one that involved an actual attack. Habituation most likely played a role in this unusual coyote behavior.
Beginning in 1988, park staff increased monitoring of coyotes along park roadsides. We experimented with scaring unwary coyotes from visitor use areas with cracker shell rounds, bear repellent spray, or other negative stimuli, but there is little indication that such techniques caused long-term term changes in individual coyote behavior. Those animals that continue to pose a threat to themselves or to humans may be translocated to other areas of the park, or even removed from the park ecosystem. Signs, interpretive brochures, and park staff continue to remind visitors that coyotes and other park wildlife are wild and potentially dangerous. They should never be fed or approached too closely, for the protection of humans and the animals.
* Information on this page provided by the NPS.
Gese, E.M. and S. Grothe. 1995. Analysis of coyote predation on deer and elk during winter in Yellowstone National Park, Wyoming. Am. Midl. Nat. 133:36-43.
Gese, E.M., R.L. Ruff, and R.L. Crabtree. 1996. Intrinsic and extrinsic factors influencing coyote predation of small mammals in Yellowstone National Park. Can. J. Zool. 74: 784-797.
Gese, E.M., R.D. Schultz, M.R. Johnson, E.S. Williams, R.L. Crabtree, and R.L. Ruff. 1997. Serological survey for diseases in free-ranging coyotes (Canis latrans) in Yellowstone National Park, Wyoming. J. Wildl. Dis. 33(1): 47-56.