INVESTIGATING THE EFFECTS OF URBANIZATION ON COUGAR FORAGING ECOLOGY ALONG THE WILDLAND-URBAN GRADIENT OF WESTERN WASHINGTON
Robins, Clint William
MetadataShow full item record
Humans have historically altered ecosystem structure through landscape manipulation, leaving “remnants,” or refuge patches of suitable habitat amidst inhospitable terrain. Large carnivores are especially vulnerable to such habitat modification because they tend to have low population densities and reproductive rates as well as wide-ranging behavior to satisfy high food requirements. Cougars (Puma concolor), by contrast, are highly resilient and have demonstrated a tolerance for fragmented and managed landscapes. The temporal influence of landscape development on cougar foraging behavior, however, is not well understood. Accordingly, I compared cougar diets assessed during two different time periods, 2004 – 2008 (Study period 1) and 2013 – 2016 (Study period 2), along a wildland-urban gradient in western Washington to determine how urbanization influences the foraging ecology of this apex predator. Generalized linear mixed model results from this investigation showed that the odds of cougar predation on synanthropic prey increased with urbanization. Ungulate usage by cougars increased over time, and the odds of ungulate predation remained relatively consistent across the wildland-urban gradient, suggesting that cougars were able to maintain similar reliance on ungulates over time and space despite potential differences in ungulate availability. The odds of rodent predation decreased with increased development, suggesting that urbanization may diminish the quality of riparian habitats in areas where wildlands abut residential landscapes. Individual differences among cougars were a significant predictor of predation on all three prey groups, and the dominant driver of cougar use of synanthrope and ungulate prey (which were primarily black tailed deer). The variation in cougar diets exhibited in this study suggests that cougar population responses to urbanization, and other forms of human disturbance, are unlikely to be uniform, and therefore, understanding the drivers that cause dietary specialization on certain prey types is a key to predicting how cougar populations will be shaped by anthropogenic landscape modification. Cougar kill locations consistently occurred in areas with low housing density despite an advancing pattern of urban growth in the region since 2004. The residential landscapes used by cougars in western Washington often fall outside city limits, and these areas have undergone limited development as a consequence of Washington state’s approach to managing urban growth. Specifically, in 1990, the Washington state legislature passed the Growth Management Act (GMA), which largely restricted urban-growth to incorporated townships and cities with the aim of protecting wildlife habitat. Washington's GMA has influenced land-use planning in a way that benefits cougars, and could be used as a model for structuring environmental policies beneficial to large carnivores elsewhere. Modeling individual differences in cougar behavior, as I have done with cougar diets in this study, could aid in mitigating cougar-human conflict by helping management agencies to identify individual cougars prone to causing depredations. Lastly, cougar reliance on ungulates has increased over time, and minimizing cougar human conflict may also require minimizing browse opportunities for deer near residences in an effort to keep foraging cougars away from homes.
- Forestry