Thursday, February 21, 2013

Roads & snakes in Saskatchewan

An eastern yellow-bellied racer (Coluber constrictor flaviventris) in Texas
Photo Credit: David Sledge.

Roads contribute significantly to mortality of snakes and can greatly increase the probability of local extinction. In North America populations of some snake species have declined or been extirpated due to road mortality. The abundance of larger snakes was reduced by more than 50% within 450 m of  a state highway (high traffic volume) and forest service system and county roads (lower traffic volume) in the Angelina National Forest in eastern Texas. Fortney and colleagues (2013) investigated road mortality as a threat to Canadian snake populations in the Grasslands National Park of Canada (GNP) area of southwestern Saskatchewan. The area has a unique snake community within Canada with six snake species: Plains Gartersnake (Thamnophis radix), Wandering Gartersnake (Thamnophis elegans vagrans), Bullsnake (Pituophis catenifer sayi), Prairie Rattlesnake (Crotalus viridis), Eastern Yellow-bellied Racer (Coluber constrictor flaviventris), and Western Hog-nosed Snake (Heterodon nasicus).

Forty-five systematic surveys of roads in the Grasslands National Park area in 2009 yielded 36 dead and 18 live snakes. Multivariate modelling revealed that proximity to hibernacula was positively correlated with presence of snakes on roads. Paved roads had a disproportionately higher numbers of snake mortality, suggesting that traffic patterns are a bigger risk factor than road use per se. Some radio-tracked Eastern Yellow-bellied Racers (2 of 17; 12%) and Bullsnakes (Pituophis catenifer sayi) (4 of 5; 80%) captured at emergence from hibernacula had road areas in their home ranges. The individuals equipped with radio-transmitters used roads and immediately adjacent areas significantly more than expected, based on their availability, suggesting possible selection for roads. Strategies to reduce road mortality of snakes should focus on key stretches of roads, such as those near winter hibernacula or riparian zones. The placement of paved roads in sensitive areas like those in and around Grasslands National Park should be carefully considered to minimize snake mortality.

Citation
Fortney, Ashley N., Ray G. Poulin, Jessica A. Martino, Dennilyn L. Parker, and Christopher M. Somers. 2012. Proximity to hibernacula and road type influence potential road mortality of snakes in southwestern Saskatchewan. Canadian Field-Naturalist 126(3): 194–203.

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