Snow cover and late fall movement influence wood frog survival during an unusually cold winter
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Understanding how organisms will respond to altered winter conditions is hampered by a paucity of information on the winter ecology for many species. Amphibians are sensitive to environmental temperature and moisture conditions and may be vulnerable to changes in winter climate. We used a combination of radio telemetry and field enclosures to monitor survival of the freeze-tolerant wood frog (Lithobates sylvaticus) during the unusually cold winter of 2013–2014. We experimentally manipulated snow cover to determine the effect of snow removal on winter survival. In addition, we placed a group of untracked frogs at locations used by tracked frogs prior to long-distance late fall movement to investigate whether late fall movement entailed survival consequences. Winter survival was highest (75.3 %) among frogs at post-movement locations that received natural snow cover. The odds of surviving the winter for frogs in the snow removal treatment was only 21.6 % that of frogs in the natural snow treatment. Likewise, paired frogs placed at pre-fall movement locations had only 35.1 % the odds of surviving as tracked frogs at post-fall movement locations. A comparison of a priori models that included microhabitat conditions measured at wood frog overwintering locations revealed that the minimum temperature experienced and the depth of the frog in the substrate explained additional variation in winter survival. Our results suggest that acute exposure to lethal temperature conditions is the most likely cause of mortality during this study, rather than energy exhaustion or desiccation. They also demonstrate the importance of snow cover to the winter survival of wood frogs.
KeywordsAmphibian Overwintering ecology Survival Soil temperature Snow cover
All applicable institutional and/or national guidelines for the care and use of animals were followed. Assistance with field work was provided by MJ Evans, JM Hessenauer, KM O’Connor, A Stupik, R Hyland, H Morway, and S Banker. F Thompson, I Ortega and M Urban commented on draft manuscripts. This project also benefited from discussion during Rittenhouse-Vokoun lab group meetings. Two anonymous reviewers provided helpful suggestions for improving the manuscript. The research was conducted under University of Connecticut animal care protocol #A13-044.
Author contribution statement
JHO and TAGR conceived and designed experiment. JHO conducted fieldwork. JHO and TAGR analyzed the data. JHO wrote the manuscript and TAGR provided editorial advice.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
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