Patterns of variation in spring emergence by black rat snakes (Elaphe obsoleta obsoleta)

Substantial individual variation in timing of emergence from hibernation has been reported among reptiles. Here we report patterns of spring emergence by black snake rat (Elaphe obsoleta obsoleta) observed at 13 communal hibernacula in eastern Ontario from 1992-1997. Because our study is at the extreme end of the species range, we expect synchronous emergence of the very short active season (about 5 months). Despite these apparent time constraints, however, the emergence period lasted an average of 40 days. Although we found significant variation in the timing of emergence among years and among hibernacula, we found no evidence of a simple latitudinal gradient in mean emergence dates. Within hibernacula, significantly higher rates of upper air temperature, maximum target air temperature explained only a small amount of variation among years in emergence dates. Larger individuals greater than average size, as predicted if early spring predation is higher for smaller snakes. Females tended to emerge slightly more than males. Condition was not a significant factor determining the timing of emergence in our population. Individuals demonstrated significant repeatability between years in the same hibernaculum. There have been significant individual variations in the date of emergence of hibernation among reptiles. However, very few studies have examined the causes of these individual variations. In this study, we report patterns in the emergence of hibernation in black dabbling elaphes (Elaphe obsoleta obsoleta) observed at 13 community hibernacula in eastern Ontario from 1992 to 1997. Because our study area is located at extreme north of the distribution of the species, we expected that snakes emerge in a synchronized way since their season of activity is very short. Despite these temporal constraints, the period of emergence of hibernation lasted on average 40 days. We found significant variation in average year-to-year emergence dates as well as hibernaculum growth. However, it was not a simple latitude gradient of average emergence dates for hibernacula. Significantly more snakes emerged from hibernation on days when the maximum air temperature was high, but year-to-year differences in temperature only partially explained annual variations in mean emergence dates. . Longer individuals emerged earlier than shorter individuals, as predicted if the risk of predation during colder spring weather conditions is lower for longer individuals. Females tended to emerge slightly earlier than males. The physical condition of the individuals was not a significant factor in determining emergence patterns in our black dwarf elaphic population.