The effects of road substrate on the Northern Pine Snake, Pituophis melanoleucus

Background/Question/Methods

New Jersey, the most densely populated state in the nation, has a dense complex of roads.  Both paved and unpaved roads fragment the globally rare Pine Barrens occupied by the Northern Pine Snake (Pituophis melanoleucus), a state threatened species. These roads can act as barriers to ecosystem connectivity, contributing to habitat fragmentation, wildlife mortality, loss of genetic corridors, and decreased reproductive success. Roads represent a major threat to slow moving herpetofauna that are extremely vulnerable to vehicular road injuries and death. The Northern Pine Snake is a large bodied, wide-dispersing species that is particularly impacted by roads in New Jersey. Of 536 reported occurrences for Northern Pine Snakes (Pituophis melanoleucus) in the New Jersey biotics database 120, or 23%, were dead on road (NJDEP, 2009). We examined the mean rate of movement of the Northern Pine Snake across three different substrates: sand, asphalt, and concrete. We tested twelve snakes (n=12) in spring, summer, and fall 2012 at the Warren Grove Gunnery Range (WGR), Burlington County New Jersey.

Results/Conclusions

Snakes had the fastest rate of movement across sand (x=0.11m/s) compared to paved substrates: asphalt (0.09m/s) and concrete (0.06m/s). These data suggest that coarser substrates facilitate increased mobility of snakes. Using the snake’s mean rate of movement of asphalt, we estimated that it would take an adult Northern Pine Snake a minimum 2.07 minutes to cross an asphalt road, from shoulder to shoulder, at a 90 degree angle. Pairing this information with the New Jersey traffic report data for three roads intersecting the study site, we calculated the number of cars a snake would likely encounter during a single traverse.  We examined the utility of under-road-culverts as mitigation of roads for locally occurring fauna, including snakes. We installed nine 12-inch diameter culverts under a new military runway at WGR to monitor wildlife movements. We documented 364 ‘visits’ at the mouth of the culverts and 54 ‘usage’ events (14.8% culvert usage by visiting fauna, including snakes). These data support that culverts are a viable option for mitigating road impacts to wildlife. To better understand the impact of roads on genetic exchange of pine snakes a landscape genetic study is warranted.