Roadkill can be disgusting, a menace to your car or even dinner. For millions of animals, though, an attempt at crossing the road ends in death for them (and for a couple hundred humans in the cars that hit them). For some animal species, these collisions can actually be the factor that tips the population down the path to extinction. Car collisions have taken particularly bad tolls on animals ranging from wombats to Florida panthers.
Determining just which critters are most likely to be hit might be helpful for developing strategies to prevent these accidents. But most of the research in this area so far has focused on specific species, populations or geographic areas, and that doesn’t necessarily translate to useful results for other species or locations. So UCLA ecologist Daniel Blumstein and his student Taylor Cook delved into past roadkill studies to dig up some trends. Their research appears in the November issue of Biological Conservation.
There are a lot of hypotheses as to what makes an animal more or less vulnerable to cars. Large-brained critters might be better equipped to avoid a collision. Scavengers might be likely to get hit when they’re munching on the carcasses of other victims. The paper details a full dozen of these ideas, many of which have been investigated with varying degrees of success. So Cook and Blumstein tried to tease out which of these hypotheses might be true by gathering information from previously published studies, giving them data from a total of 80 mammal and 99 bird species living on three continents (North and South America and Australia).
The team found a few trends, many having to do with diet. Among mammals, omnivores were especially vulnerable. The most vulnerable birds were herbivores and omnivores. Carnivores of both categories had the lowest rate of becoming roadkill, but there seemed to be far more of them killed than would be expected based on their rarity, the researchers say. There was also some evidence that social animals were less likely to end up dead in the road.
Why might diet matter? “Diet type tends to be associated with a suite of life history factors, such as range size, mobility and speed and perhaps it is diet that holds together this syndrome of vulnerability,” the researchers write. Translation: They don’t know and aren’t going to speculate.
But they do say their results point to potential new ways to reduce roadkill. The most successful strategies already in use are road signs for drivers and fences that deter animals from crossing the road. “It may be possible to repel the most vulnerable animals by removing food that is specifically attractive to them from the roadside,” the researchers write. Figuring out just how to do that, though, will probably be difficult. It’s been tried and failed with moose, for instance. And omnivores eat so many different things that removing the food that lures them to the roadside might prove impossible. But carnivores might be deterred using the same methods that repel them from livestock, Cook and Blumstein speculate. Given that some of these animals are naturally rare and humans keep doing things that push them toward extinction, it might be worth a try.