Habitat Selection of Black Ratsnakes (Pantherophis obsoletus) in the Western Piedmont of North Carolina

E. Pierson Hill, William J. Johnson, Michael E. Dorcas

Habitat fragmentation is a critical conservation issue, especially in areas of human development. Species whose ranges are fragmented may experience higher mortality rates due to anthropogenic disturbances such as pollution, car traffic, and habitat alteration (Baldwin and Machand, 2004; Dodd and Smith, 2003; Crooks and Soule, 1994). However, it is possible that some species may actually benefit from habitat fragmentation due to the creation of edge habitat. Edge habitats can present a wide array of conditions that vary considerably from adjacent habitats such as temperature, vegetation structure, and faunal composition. Animal species that are able take advantage of the edge habitats may proliferate in a fragmented landscape while sympatric species may suffer population declines under the same conditions. In order to make educated decisions towards conservation of certain species, it is important to know how they react to habitat fragmentation and the creation of edge habitat.

The Black Ratsnake (Pantherophis obsoletus) is a large generalist species that is common to the Piedmont of North Carolina. Previous studies have shown Black Ratsnakes to flourish in fragmented landscapes, edge habitats, or those with high edge-to-area ratio (Blouin-Demers and Weatherhead, 2002; Heske, 2000; Gates, 1998; Durner and Gates; Weatherhead and Charland, 1985) and it is likely that Black Ratsnakes on the DCEP are following suit. However, P. obsoletus is well known for its variable morphology over its extensive range. It is similarly possible that aspects of the species' behavior, such as microhabitat selection, differs between the various geographic regions in which the species is found.

The study took place on the Davidson College Ecological Preserve, an approximately 200-acre parcel of land adjacent to the Davidson College campus in northern Mecklenburg County, NC. It is composed of a patchwork of disturbed, regrowth, and intact forests that are transected by several power cuts. The study area extended moderate distances into surrounding areas of human development that range from cattle pasture to private residences.

An aerial photo of The Davidson College Ecological Preserve (outlined in red) and surrounding area.

Fourteen Black Ratsnakes on the DCEP were captured by hand during chance encounters and then surgically implanted with radio transmitters. They were then released where originally found after a 1-2 day recovery time. Each snake was tracked over a variable length of time spanning from March 2002 to August 2004. Each individual was tracked twice a week and recorded for GPS location, macro/microhabitats occupied, behavior, and environmental conditions. Using this data, we will be scrutinizing all aspects of habitat selection by Black Ratsnakes such as the surrounding macrohabitat and microhabitat as well as the snakes’ height above ground. Macrohabitat and edge habitat selection by type will be measured through Ivlev’s index (Brito, 2003), which relates number of observations within a habitat class to the available area of that habitat class. We will also use GIS to determine how often snakes were located in macro and edge habitats. Microhabitat will be evaluated using polytomous logistic regression (Cross and Petersen, 2001) which will allow us to assign use-intensity categories to microhabitats.

Radiotransmitter implantation
Radiotracking a Black Ratsnake


Literature Cited

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