Estimating population densities from radio-telemetry data for the northern pine snake in New Jersey

Background/Question/Methods

Understanding population dynamics is paramount for successful management and long-term conservation of a rare species.  The northern pine snake, Pituophis melanoleucus, is a state-threatened species that is declining in New Jersey. Unfortunately, quantitative population data is lacking and the northern pine snake as this semi-fossorial cryptic species is difficult to census.  The northern pinesnake remains vulnerable as a result of potential status delisting, habitat loss, habitat fragmentation, and isolation. We developed a “population density model” for estimating the number of pine snakes at the Warren Grove Gunnery Range (WGR). The model estimates the number of snakes per-unit-area (density) within preferred northern pine snake habitat (pine-oak forest) from radio-telemetry (spatial ecology) data.

Results/Conclusions

We estimate that an average of 229 adult snakes occurred in the local population on WGR, a site of 3880 hectares. The average estimated density is one individual per 16.9ha.  These data were extrapolated to estimate the current, historical, and rate of decline of the northern pine snake population in New Jersey. We estimated that the northern pine snake has declined from an average of 16,476 snakes in 1986 to 15,188 snakes in 2007, a decline of 61 adult northern pine snakes per year.  We plan to test the density model at both the local (WGR) and landscape (Pinelands) scale for better resolution and precision of population estimates.  Understanding population size and trends is imperative for improved conservation management of this threatened species.