IUCN / SSC Cat Specialist Group - Digital Cat Library |
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| Cruickshank, H.S. | |
| Prey selection and kill rates of cougars in northeastern Washington | |
| 2004 Full Book | |
We investigated prey selection and kill rates of cougars in northeastern Washington from 2002-2004, in a sympatric white-tailed deer and mule deer system. We tested two competing hypotheses of prey selection, "prey switching" and "apparent competition". We developed a sightability model which corrected ground counts of white-tailed deer and mule deer using life-sized deer decoys to calculate relative prey availability. A logistic regression sightability model tested for effects of group size, distance, and habitat on deer sightability, then predicted relative numbers (availability) of both deer species on transects. To estimate use of prey by cougars, we examined 60 cougar kills. White-tailed deer comprised 60% of the kills (mule deer comprised 40%), a proportion larger than the study area's prey population (70% white-tailed deer vs. 30% mule deer). Cougars selected for mule deer across the entire study area. We also detected strong seasonal changes in prey selection, with cougars strongly selecting for mule deer in summer, but not during winter. Mean annual kill rate was 6.68 days per deer killed. Kill rates did not differ between seasons or deer species. Habitat characteristics of kill sites did not differ significantly between white-tailed deer and mule deer kills. These findings are consistent with the apparent competition hypothesis and suggest that the current decline in mule deer numbers in northeastern Washington is caused by an abundant invading primary prey species (white-tailed deer) and a related increase in predation on the secondary prey species (mule deer) during summer months. |
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