Seasonal Foraging Ecology of Non-Migratory Cougars in a System with Migrating Prey

Abstract

We tested for seasonal differences in cougar (Puma concolor) foraging behaviors in the Southern Yellowstone Ecosystem, a multi-prey system in which ungulate prey migrate, and cougars do not. We recorded 411 winter prey and 239 summer prey killed by 28 female and 10 male cougars, and an additional 37 prey items by unmarked cougars. Deer composed 42.4% of summer cougar diets but only 7.2% of winter diets. Males and females, however, selected different proportions of different prey; male cougars selected more elk (Cervus elaphus) and moose (Alces alces) than females, while females killed greater proportions of bighorn sheep (Ovis canadensis), pronghorn (Antilocapra americana), mule deer (Odocoileus hemionus) and small prey than males. Kill rates did not vary by season or between males and females. In winter, cougars were more likely to kill prey on the landscape as: 1) elevation decreased, 2) distance to edge habitat decreased, 3) distance to large bodies of water decreased, and 4) steepness increased, whereas in summer, cougars were more likely to kill in areas as: 1) elevation decreased, 2) distance to edge habitat decreased, and 3) distance from large bodies of water increased. Our work highlighted that seasonal prey selection exhibited by stationary carnivores in systems with migratory prey is not only driven by changing prey vulnerability, but also by changing prey abundances. Elk and deer migrations may also be sustaining stationary cougar populations and creating apparent competition scenarios that result in higher predation rates on migratory bighorn sheep in winter and pronghorn in summer. Nevertheless, cougar predation on rare ungulates also appeared to be influenced by individual prey selection.

Recolonizing wolves influence the realized niche of resident cougars

“…Ungulates included elk, mule deer, moose (Alces alces), bison (Bison bison), pronghorn (Antilocapra americana), bighorn sheep (Ovis canadensis), and a small number of white-tailed deer (Odocoileus virginianus). Deer, elk, bighorn sheep, and pronghorn exhibited seasonal migrations (Sawyer et al 2005;Smith 2007;Elbroch et al 2013); elk were heavily harvested (10-12 % annually) in efforts to reduce their population, and deer and moose supported limited, male-only harvest rates. Bighorn sheep too supported a limited harvest of either sex (http://wgfd.wyo.gov/web2011/ HUNTING-1000184.aspx).…”

“…Following well-established elk migration dates in the study area, we defined winter as December 1 of one year through May 31 of the next year, and summer as June 1 through November 30 of the same year (Elbroch et al 2013 To account for variable number of prey killed by individual cougars, we quantified each individual cougar's prey selection as the proportions of prey killed by each cougar, before conducting any population level analyses. We excluded non-ungulate prey for our analyses and divided the remainder into proportions of elk, deer, and "other ungulates," which included bighorn sheep, moose, and pronghorn (Fig.…”

“…Following Bartnick et al's (2013) hypothesis that cougars in the SYE are increasingly selecting deer instead of elk in the presence of wolves, we tested for changes in actual cougar prey selection between 2002 and 2012, a period during which wolves increased from 15 to as high as 91 in the system (a 600 % increase). We hypothesized that we would detect a shift from elk to deer only in summer, because in winter deer migrate almost entirely out of the study system, thus limiting the opportunities for prey switching (Elbroch et al 2013). We predicted cougar prey selection might switch from elk to deer because of increased encounter rates with deer related to preferential hunting, an increase in cougar use of more complex habitats where deer are more abundant (Kortello et al 2007), or declining elk availability in the study area.…”

“…The SYE is a large undeveloped landscape where ungulate prey exhibit seasonal migrations (Sawyer et al 2005;Smith 2007;Nelson et al 2012;Elbroch et al 2013) and winter snows force wolves, cougars, and their prey to share lower elevations in late winter (Kortello et al 2007;Ruth et al 2011;Elbroch et al 2013). Evidence for competition between the two species implies that ongoing competition with wolves limits the realized niche of cougars.…”

Cougars (<i>Puma concolor</i>) Killed by North American Porcupines (<i>Erethizon dorsatum</i>)

“…The study took place in the Southern Yellowstone Ecosystem (see Elbroch et al 2013 for a description of the study area). All collars were equipped with mortality sensors, which alerted us when collars had not moved for more than 8 h. We investigated sites where Cougars died to determine the cause of death.…”