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.