HABITAT FEATURES OF BLACK RAT SNAKE HIBERNACULA IN ONTARIO

Suitable over-wintering habitat is critical to the survival of snake p opulations at higher latitudes. The identification and protection of t raditional, communal hibernation sites (hibernacula) is important for the conservation of threatened species, while the assessment of hibern acula availability may help determine the extent to which population d istributions are limited by habitat suitability. In this paper, we qua ntified surface habitat characteristics of 10 hibernacula and the comp osition of basking trees used by a threatened population of black rat snakes (Elaphe o. obsoleta) at the northern limit of the species' rang e. Hibernacula were typically situated on relatively rocky, south-faci ng slopes. The co-occurrence of these features was sufficiently unique as to distinguish hibernacula from (1) a series of random sites, but not from (2) a set of intuitively identified ''potential hibernacula'' in the surrounding landscape. This implies that additional requisite elements (e.g., underground structure and micro-climatic conditions), which we were unable to quantify, set actual hibernacula apart from si tes that appear to be otherwise suitable (i.e., ''potential hibernacul a''). Basking trees found at hibernacula tended to be relatively large and decayed or dying with numerous cavities. Unused trees exhibiting these characteristics were also available at both random sites and pot ential hibernacula indicating the suitability of those sites for baski ng. Our results suggest that rat snake hibernacula cannot be predictab ly located by simply searching for key surface habitat features in the landscape. The current data are equivocal as to whether or not this m ost northern population is limited by the availability of suitable ove r-winter habitat since the possibility that essential subterranean fea tures of hibernacula are limiting remains to be tested. We recommend t he continued use of radio-telemetry to identify and protect additional hibernacula, the preservation of basking trees at known hibernacula, and further research to determine the internal structure and micro-env ironments of hibernacula.