The behavioral response of basking Northern water ( Nerodia sipedon ) and Eastern garter ( Thamnophis sirtalis ) snakes to pedestrians in a New Jersey park

Abstract

Considerable attention has been devoted to the effects of people on birds and mammals, usually in wilderness or semiwilderness, but relatively little has been directed at reptiles in heavily populated areas. This paper examines the role of investigators and pedestrians on Northern water (Nerodia sipedon) and Eastern garter (Thamnophis sirtalis) snakes basking along a canal in New Jersey. The protocol involved 1–3 investigators approaching snakes that were basking between a path and the Raritan Canal. Investigators walked along the path until they were perpendicular to the snake, observed them for 60 seconds, and then approached them directly. Nearly 40% of the variability in distance to first respond for water snakes (N = 135) was accounted for by distance the snake was from the path, number of observers, and number of people currently using the trail, while 27% of the variability in time to respond was accounted for by number of observers, distance to path and water, and air temperature. There was no significant model for garter snakes (N = 33). Nearly 30% of water snakes, but only 5% of garter snakes, responded during the approach of an observer, and another 32% of water and 45% of garter snakes responded within the first minute of stopping on the trail nearest to them. Water snakes responded when the observer was farther away from them than did garter snakes. As the number of pedestrians on the path increased, water snakes responded when people were farther from them, but there were no differences for garter snakes in response distance. These data indicate differences in response, with water snakes responding sooner than garter snakes. Few garter snakes responded when they were over 150 cm from the path, while a quarter of the water snakes responded when they were from 200 to 300 cm from the path, suggesting that paths should be at least 400 cm from water, providing safe basking sites for water snakes. Further, the data indicate that walking past snakes without stopping results in less disturbance than stopping to watch them.