Roadkill Distribution at the Wildland-Urban Interface

The growing wildland-urban interface is a frontier of human-wildlife conflict worldwide. Where natural and developed areas meet, there is potential for negative interactions between humans and wild animals, including wildlife-vehicle collisions. Understanding the environmental and anthropogenic factors leading to these collisions can inform transportation and habitat planning, with an objective of reducing animal mortality and human costs. We investigated spatial, temporal, and species-specific patterns of roadkill on Interstate-280 (I-280) in California, USA, and examined the effects of land cover, fencing, lighting, and traffic. The highway is situated just south of San Francisco, dividing a large wildlife refuge to the west from dense residential areas to the east, and therefore presents a major barrier to wildlife movement. Areas with a higher percentage of developed land east of I-280 and areas with more open space on the west side of I-280 were associated with an increase in overall roadkill, suggesting that hard boundaries at the wildland-urban interface may be zones of high risk for dispersing animals. This pattern was especially strong for raccoons (Procyon lotor) and black-tailed deer (Odocoileus hemionus). The presence of lighting correlated with increased roadkill with the exception of coyote (Canis latrans). Contrary to our expectations, we found weak evidence that fencing increases roadkill, perhaps because animals become trapped on roadways or because fencing is not sufficient to block access to the road by wildlife. Finally, we found strong evidence for roadkill seasonality, correlated with differences in movement and dispersal across life-history stages. We highlight the value of citizen-science datasets for monitoring human-wildlife conflict and suggest potential mitigation measures to reduce the negative effects of wildlife-vehicle collisions for people and wildlife.