All bobcats in three Southern California mountain ranges seem to shun roads whenever possible, but males run a higher risk of being killed by vehicular traffic, according to a recent study. Vehicle collisions are a leading cause of bobcat deaths in California, and the study underscores the importance of keeping wildlife in mind when planning residential and other development.
The study, published in the journal Biological Conservation, examined the daily habits of bobcats in the Chino Hills, the Santa Ana Mountains, and the San Joaquin Hills. Fifty-two bobcats were trapped, examined, and then released with GPS-tracking collars, and their movements plotted to see how the presence of roads affected their daily movements and the size of the territories they occupied.
Bobcats will cross roads if they have to, it turns out, but they prefer not to. More roads in a bobcat's territory apparently means lower quality habitat, which means the cats much stake out larger territories in areas with lots of roads to make a living. And male bobcats, whose territories are larger than females, end up crossing roads more often, exposing them to greater risk of being killed while crossing.
In the study, done by Sharon Poessel of Colorado State University at Fort Collins and the U.S. Geological Survey along with six colleagues from both those institutions, bobcats were collared and tracked between 2002 and 2009. The team analyzed how bobcats responded to the presence of both primary roads (freeways, essentially) and secondary roads (high-traffic arterials) in and near the cat's ranges. The study didn't measure the cats' responses to lower-traffic roads or suburban streets.
The results showed a strong aversion to freeways and other primary roads: of all the cats studied, only a few females in the Chino Hills ventured close to primary roads; their typical distance from busy roads averaged about a fifth of a mile, while other cats stayed three quarters of a mile or more from primary roads. Of more than 3,700 "movement tracks" mapped by the team -- essentially, trips the collared cats took during their periods of activity -- only 248 crossed primary roads, suggesting that bobcats strongly prefer to stay away from freeways.
Male bobcats were about three times as likely as females to cross primary roads, and about four times as likely to cross secondary roads.
Other studies have shown that bobcats will readily use underpasses to cross major highways. That offers a relatively straightforward way to keep bobcat habitat connected across highway corridors, say the authors. "The continued implementation of such strategies," they write, "should benefit the conservation of bobcats and other species by increasing survival, movement, gene flow, and landscape connectivity in fragmented urban systems."