Cooperative Fish and Wildlife Research Units Program: Headquarters
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Poikilothermic species, such as amphibians, endure harsh winter conditions via freeze-tolerance or freeze-avoidance strategies. Freeze-tolerance requires a suite of complex, physiological mechanisms (e.g., cryoprotectant synthesis), however, behavioral strategies (e.g., hibernal habitat selection) may also affect thermoregulation during hibernation. We investigated the hibernal ecology of the freeze-tolerant Wood Frog (Lithobates sylvaticus) in Maine’s Quebec/New England Boundary Mountains ecoregion. Our objectives were to characterize the speices’ hibernacula microclimate (i.e., temperature, relative humidity), evaluate hibernal habitat selection, and describe the spatial arrangement of breeding, post-breeding, and hibernal habitats. We monitored 15 Wood Frogs during two winters (2011/12: n = 10; 2012/13: n = 5), measured hibernal habitat features at micro (2 m) and macro (10 m) spatial scales, and recorded mircoclimate hourly in three strata (hibernaculum, leaf litter, ambient air). We compared these data to that of 57 random locations with logistic regression models, Akaike Information Criterion, and Kolmogorov-Smirnov tests. The top-ranked a priori micro- and macrohabitat model included three covariates: distance to nearest breeding site, distance to post-breeding activity center, and percent canopy cover. Model averaging indicated that canopy cover (-), leaf litter depth (+), and number of logs and stumps (+) were important predictors of Wood Frog hibernal habitat. Hibernal habitat features facilitate snowpack accumulation, which insulates hibernating frogs from extreme and variable above-ground air temperatures. Altered winter temperature and precipitation patterns due to climate-change may reduce snowpack insulation, facilitate greater temperature variation in the underlying hibernacula, and potentially compromise Wood Frog winter survival.