Highway mortality of snakes in the sonoran desert of southern Arizona

We present an algebraic method for estimating highway mortality in snakes, based on careful data collection during low-speed driving on paved roads. A total of 368 snakes (104 live, 264 dead) were recorded over four years on State Route 85 from Why to Lukeville, Pima Co., Arizona, during 15 525 km of road-cruising; mostly within Organ Pipe Cactus National Monument. We computed an estimate of 2383 snakes killed 13·5/km/year) during the four years on this stretch of pavement, estimate that actual numbers killed would be closer to 4000 (22·5/km/year). Two taxa of special conservation interest, the Mexican rosy boa Lichanura trivirgata and the Organ Pipe shovelnosed snake Chionactis palarostris, appear to be relatively strongly impacted by highway mortality. Overall, along our 44·1 km transect, the estimated highway mortality amounts to removal of 5 km² of snake population over the four years of study. It is clear that roadways, especially if paved, substantially damage snake populations.