Estimating cougar population trends in Oregon with integrated population models

Background/Question/Methods

Cougar (Puma concolor) populations have increased substantially in many areas of the western U.S. since the mid-20^th Century.  Coupled with an increasing human population and distribution, increased levels of interactions and conflicts with cougars have occurred in some areas.  Our objectives were to predict historical trends in population size and structure from age-at-mortality data collected in Oregon.  Oregon Department of Fish and Wildlife currently uses a deterministic population reconstruction model; we developed a Bayesian Hierarchical Model that could fully account for variability in input data and provide credible intervals for final predictions.  We used mortality data collected through the state agency mandated check-in process that described sex, age, and location of cougars killed by humans during 1987–2009.  We developed models that allowed both harvest and other anthropogenic mortality to be constant, age dependent, time dependent, or age and time dependent.  Population estimates were made for each sex in all cases.  We evaluated models fitted to data from each of 6 Oregon cougar management areas independently.  We tested the models against simulated data to confirm the extent to which the models accurately capture trends in population size and structure.

Results/Conclusions

Our results qualitatively match previous trends from the deterministic models, but the new model is more thoroughly tested and provides credible intervals on predictions. Cougar populations have increased in all management areas, sometimes dramatically. Harvest mortality was sex specific prior to 1994, but does not differ between the sexes since the use of hounds for hunting was outlawed in 1994. Our results should aid management decisions related to understanding cougar-livestock conflicts and cougar-ungulate relationships at regional scales, by predicting the population effects of future changes in policies or regulations related to cougar harvest.