The effect of temperature change on the behavior of the Northern Pine Snake and implications for climate change

Background/Question/Methods

Because snakes are poikilotherms the temperature of their surroundings influences their behavior, ecology, and physiology. Although studies have examined the spatial ecology, habitat use, and long-term hibernacula use of Pituophis melanoleucus (Northern pine snake) in the New Jersey Pine Barrens, few have focused on the influence of seasonal temperature variation on snake behavior. The New Jersey population of P. melanoleucus is at the limit of its northern range where spring temperatures are variable and in recent years mean spring temperature has arrived earlier. These changes may cue earlier egress from overwintering dens. This study elucidates the thermal ecology of the Northern pine snake and describes it in the broader context of climate change.

Pine snakes were tracked in 2010 (N=21), 2011 (N=32), and 2012 (N=21) on Warren Grove Gunnery Range in Burlington County, NJ using radio-telemetry from the time of egress from hibernacula until ingress to overwintering sites. Air and substrate surface temperatures were recorded for each tracking event as well as whether or not the snake was surface active. This data was used to determine the operative temperature (air/soil) of pine snakes as well as to calculate mean linear distance traveled per day (m/day).

Results/Conclusions

Snakes egressed starting 7 April (2010), 10 April (2011), and 23 March (2012) when mean daily temperatures were 27°C, 19°C, and 17°C, respectively.  In March 2012 two snakes were found dead within one meter of hibernacula; mortality was attributable to an unusual early warming period followed by night temperatures falling below freezing.

Snakes were most surface active when temperatures ranged from 20 to 25°C (air) and 30 to 35°C (soil). Highest surface activity was observed in May in 2010, 2011, and 2012 when average ambient temperatures were 19.4°C, 18.8°C, and 19.6°C, respectively. In all years, highest average monthly temperatures corresponded with a drop in surface activity. Mean linear distance traveled per day (pooled for 2010 and 2011) was greatest in June (x̅=113m;+/-25m) and July (x̅=105m;+/-31m). Although more long-term data is needed, these data suggest that shifts in temperature regimes have the potential to alter timing of egress, ingress, and dispersal of the Northern pine snake.