Proceedings of the Seventh Mountain Lion Workshop

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COUGAR PREDATION ON PREY IN YELLOWSTONE NATIONAL PARK: A
PRELIMINARY COMPARISON PRE- AND POST-WOLF REESTABLISHMENT
TONI K. RUTH, Wildlife Conservation Society, 2023 Stadium Dr. Suite 1A, Bozeman, MT
59030, USA, email: truth@montanadsl.net
POLLY C. BUOTTE, Wildlife Conservation Society, 2023 Stadium Dr. Suite 1A, Bozeman, MT
59030, USA, email: polly_thornton@hotmail.com
KERRY M. MURPHY, Yellowstone Center for Resources, P.O. Box 168, Yellowstone National
Park, Mammoth, WY 89210, USA, email: kerry_murphy@nps.gov
MAURICE G. HORNOCKER, Wildlife Conservation Society, 2023 Stadium Dr. Suite 1A,
Bozeman, MT 59030, USA
Abstract: On Yellowstone National Park’s Northern Range cougars and wolves rely on
economically important prey species, particularly elk. Understanding how these large carnivores
partition prey resources and their combined affect on prey is important for management and
conservation of cougars, wolves, and ungulate species. As part of a cougar-wolf interactions
study, we quantified predation rates and prey selection by cougars on Yellowstone’s northern
range prior to (Phase I) and post wolf (Phase II) reestablishment. During Phase II, cougars spent
an average of 3.7 days at kills and 4.4 days between each kill. The mean annual rate of cougar
predation in Phase I was 9.4 (SD = 4.0; 95% CI = 7.8 to 11.0) days per ungulate kill, and
10.9(SD = 8.5; 95% CI = 6.7 to 15.1) days per ungulate kill in Phase II. Rate of predation varied
by cougar social class. When converted to biomass killed per day, cougars averaged 12.2 kg per
day during Phase I and 12.9 kg per day during Phase II. We documented a total of 306 and 256
positive and probable cougar kills during Phase I and Phase II, respectively. During Phase II,
70% (n = 179) of cougar kills were elk, 17% (n = 43) were mule deer and 13% (n = 34) were
other prey. During both Phase I and II more than 50% of cougar kills were elk calves, with cow
elk making up the next largest category. During Phase I, cougar predation was neither a major
source of mortality nor a significant factor limiting the numbers or growth rates of elk and mule
deer populations in northern Yellowstone. Cougars present on the study area killed 2-3% of the
elk and 3-5% of the mule deer estimated to be available during 5 years spanning the Phase I
study. Simultaneous to our Phase II study, the Yellowstone Wolf Project quantifies wolf
predation rates and prey selection. Cougars killed proportionally more elk calves and fewer bull
elk than wolves between 1998 and 2002. We are continuing our data collection and analyses and
plan to: 1) compare cougar and wolf per capita rate of predation, 2) contrast femur marrow fat
content of cougar and wolf kills, by season killed and prey age, and 3) compare yearly off-take
of elk and mule deer by cougars and wolves. Cougar per capita predation rate averaged across
social classes was 0.06 kills/cougar/day. When kittens were included with maternal females, that
group had the lowest predation rate of 0.01. Without including kittens, maternal females
averaged 0.15. Subadult males had an equally high rate of 0.15. Wolf predation ranged from
0.03 to 0.078 kills per wolf per day (Smith et al., In Press).
PROCEEDINGS OF THE SEVENTH MOUNTAIN LION WORKSHOP