The Natural History of the Northern Black Racer (Coluber Constrictor Constrictor) in South-Central Pennsylvania

Abstract

Long-term species surveys are effective tools for identifying changes in population demography which is of particular importance for those in threatened habitats such as grasslands. Due to their cryptic nature, snakes can benefit greatly from these types of surveys but multiyear surveys for snakes are rare in Pennsylvania and the surrounding region. We conducted coverboard surveys of the grassland specialist Northern Black Racer (Coluber constrictor constrictor) over eight years separated into two sampling periods (2008-2012 and 2015-2017) across a habitat-mosaic in south-central Pennsylvania. We recorded information on their body size, demography, and monthly activity. We compared these traits between the sampling periods to determine how they vary over time. A total of 70 Northern Black Racers were captured during this project. As expected, grasslands were heavily exploited by Northern Black Racers highlighting their importance to this species. There was a shift from relatively larger-bodied, older individuals towards relatively smaller-bodied, younger individuals between the sampling periods, but the sex ratio remained unchanged. Monthly activity of adults was unimodal in both sampling periods, but the month of peak activity varied and there was a possible effect of precipitation on this difference. The change in age structure between the sampling periods suggested that a widespread mortality event, possibly from exceedingly cold overwintering conditions, may have culled older individuals resulting in a younger cohort to fill the void. As Northern Black Racers are an important grassland predator, our data show the benefits of long-term surveys through detecting changes in demographics that could potentially influence long-term survival of a population.

Demographic traits of an Eastern Gartersnake, <i>Thamnophis sirtalis sirtalis</i>, population in two different habitats

“…Likewise, a relatively constant pattern in adult body sizes and body size ratios between sexes was evident among Pennsylvania sites other than those of Meshaka and Delis (2014). To that end, the presence of racers appears to select for fewer and larger individuals of other snake species (Kjoss and Litvaitis 2001;Dallas et al 2021). In Pennsylvania as a whole, mean body sizes of adults were small in males (mean = 33.8 cm) and females (mean = 43.9 cm) (Hulse et al 2001).…”