The omnivore's dilemma: Diet explains variation in vulnerability to vehicle collision mortality

As human populations increase, roads are expanded and traffic increases, leading to more opportunities for animal-vehicle collisions. Roadkill is a serious threat to animal populations, and has the potential to drive threatened populations extinct. Despite this widespread damage, what makes a species' particularly vulnerable to being hit by vehicles is not well understood and mitigation attempts have been largely unsuccessful. Previous studies have found that animals are more likely to be killed in certain areas (hotspots) and that species are killed at differential rates. While there have been some suggestions that variation in roadkill rate is correlated with life history traits, such as body size and diet, most of these studies have been on a small scale and therefore are not necessarily generalizable. We aimed to explain variation in roadkill vulnerability on a larger scale by performing a formal comparative analysis of published roadkill data from around the world. Focusing on birds and mammals, we compiled data on rates that species were struck and killed, then sought to identify the life history and natural history correlates of vulnerability. We found that diet explained a significant amount of variation in the rate of roadkill, with omnivorous mammals and herbivorous birds having the highest rates within their respective classes. Mitigation attempts should target these especially vulnerable types to increase efficiency and efficacy.