Dynamics and viability of a cougar population in the Pacific Northwest

by 1979- Lambert, Catherine Marie

By Catherine Marie Sarah Lambert, M.S. Washington State University December 2003 Chair: Robert W. Wielgus Cougar (Puma concolor) populations are believed to be at high density and increasing throughout western North America, especially in the Pacific Northwest, as evidenced by increasing cougars/humans encounters. Harvest rates have increased as a result. To test this hypothesis, I determined the density, fecundity, survival, and growth rate of a cougar population in northeastern Washington, northwestern Idaho, and southern British Columbia. From 1998 to 2003, 52 cougars were captured, radio-collared, and monitored. I recorded fecundity through den site investigation and snow tracking, and mortality by weekly telemetry. Survival rates were estimated for kittens (0-1 yr), yearlings (1-2 yr), and adult (2-12 yr) males and females. Average overall density was 1.09 cougars/100km2 or 0.46 adults/100km2. I estimated the litter size at 2.53 kittens, the birth interval at 18 months, the proportion iv of reproductively successful females at 0.75, and the age of first reproduction at 30 months, for a maternity rate of 0.63 male or female kitten/year/adult female. Average survival rate for all radio-collared cougars was 0.59, 0.77 for adult females, 0.44 for adult males, 0.37 for yearlings, and 0.57 for kittens. Hunting accounted for 92% of the mortalities of radio-collared cougars. Age- and sex-specific survival and fecundity were entered into a stochastic two-sex matrix model. I used computer simulations to determine the stochastic growth rate of the population and to assess its viability over 25 years. The annual stochastic growth rate of this population was l = 0.80 (95%CI = 0.11). Starting with a total initial abundance of 357, the median times to fall below a demographic collapse (N = 30 adults) and extirpation (N = 0) were 8.5 and 25.9 years. My findings suggest that, contrary to popular belief, cougars in the Pacific Northwest are currently at low to moderate densities and are declining. Alternative hypotheses may account for the increased conflicts between cougars and humans in this area. v