Slide 1

The influence of ambient and den temperature on the above-ground activity of woodchucks (Marmota monax) in south-central Pennsylvania Mary Riley and Bradley Rehnberg Department of Biological Sciences, York College of Pennsylvania Seasonal timetable In order to survive the physiological costs of hibernation and successfully reproduce upon emergence, woodchucks must acquire the necessary fat stores during spring, summer, and fall (Davis 1976). Grizzell (1955) noted above-ground activity to be limited to only 12 h per day. Typically woodchuck activity displays a bimodal distribution in the summer favoring morning and evening periods, and a unimodal distribution in the spring and fall favoring midday periods (Barash 1989). Social interactions are early in the growing season as adults are both establishing their territories and mating. Interactions diminish as the growing season progresses (Bronson 1964; Maher 2006). Why dwell in a den? Dens are constructed below the frost line in well- drained soils with a preference for loam and sandy loam soils (Moss 1940). Woodchucks tend to forage near their dens, as dens provide protection from both predators and most environmental extremes (Reichman and Smith 1990). Although winter den temperatures are only slightly higher than ambient, the progression of winter den temperatures to summer den temperatures has been found to be very gradual. This allows dens to remain much cooler during the summer and function as a refuge from high ambient temperatures (Zervanos and Salsbury 2003). Objective Assess above-ground activity of the woodchuck as influenced by ambient and den temperature during their active season. Hypothesis Hypothesis Woodchucks will not go above ground during high ambient temperatures. Conclusion Den temperatures remained relatively constant throughout the day and closely followed den temperature data gathered by Zervanos and Salsbury (2003). This reinforces the ability of the den to function as a refuge during the warmer months. Overall activity greatly increased in the fall evenings preceding hibernation. This was consistent with previous literature that states woodchucks display a unimodal distribution of activity in the fall as temperatures become cooler (Barash 1989). The presence of midday activity even when ambient temperatures exceeded 30C and overall lack of morning activity was unexpected. External factors to ambient temperature including location along the Codorus and consistent morning human traffic may have also influenced the regulation of activity periods. Behavioral Observations Observed from late June 2010 through mid-November 2010 for a total of 18 observations. An observation was comprised of three 1-hour intervals in the morning, midday, and evening. The aim was to quantify the number of woodchucks present and total time spent above-ground. Data Analysis Summer is defined to include measurements from June, July, and August (n=9) while fall includes measurements from September, October, and November (n=9). The mean change in temperature between dens and ambient was determined. Statistically assessed mean number observed and mean time spent above ground with a two-way ANOVA and Bonferroni Post test. Methods Results Acknowledgements Stam Zervanos and June Brown for their assistance throughout the development and execution of my thesis. Bruce Smith and the Army Corp of Engineers for assisting in locating the study area. Jen Butts for accompanying me during summer evening observations. Michael Riley for a multitude of reasons. Literature Cited Barash, D. P. 1989. Marmot sociology and behavior. Stanford University Press, Standford CA. Davis, D. 1976. Hibernation and circannual rhythms of food consumption in marmots and ground squirrels. The Quarterly Review of Biology 51:477-514. Grizzell, R.A. 1955. A study of the southern woodchuck, Marmota monax monax. The American Midland Naturalist 53:257-292. Maher, C.R. 2006. Social organization in woodchucks (Marmota monax) and its relationship to growing season. Ethology 112:313- 324. Maher, C.R. 2009. Genetic relatedness and space use in the behavorially flexible species of marmot, the woodchuck (Marmota monax). Behavioral Ecology and Sociobiology 63:857-868. Moss, A.E. 1940. The woodchuck as a soil expert. The Journal of Wildlife Management 4: 441-443. Reichman, O.J. and Smith, S.C.1990. Burrows and burrowing behavior by mammals. Current Mammalogy 2:197-244. Zervanos, S.M. and Salsbury, C.M. 2003. Seasonal body temperature fluctuations and energetic strategies in free-ranging eastern woodchucks (Marmota monax). Journal of Mammalogy 84: 299-310. Ambient and Den Temperature Measurements Manually inserted thermister probes into den entrances. Data logger recorded ambient and den temperatures for four roughly 2- week intervals. Figure 1. Area where study was conducted. White circles indicate dens with single entrances (n=21) and colored circles indicate dens with multiple entrances (n=33). Only defined zones were included during observations. Den temperature collections were taken from den entrances within and outside of the zones.