Cougar predation on bighorn sheep in southwestern Alberta during winter

Predation by cougars (Puma concolor) upon bighorn sheep (Ovis canadensis) was studied in southwestern Alberta during winters from 1985–1986 to 1993–1994. We examined 320 kills and found that ungulates provided >99% of the biomass consumed by cougars in November–April. All ungulate species found within the study area were taken by cougars. Predation on bighorn sheep varied greatly from year to year; cougars were known to kill 0–13% of the November sheep population, and 0–57% of over-winter sheep mortality consisted of known cougar kills. Of 29 bighorns killed by cougars, 13 were lambs. The remainder ranged in age from 1 to 17 years and included 9 ewes and 7 rams. Cougar predation on bighorn sheep appears to be largely an individual, learned behaviour; most cougars rarely killed sheep, but some preyed heavily upon them. One female killed 9% of the population and 26% of the lambs over a single winter. For mountain-dwelling ungulates that occur in small groups, the presence of one or a few individual specialist predators may strongly and unpredictably influence demography and behaviour.