Pre-Wolf Research
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-
istributed 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.
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