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PLoS One. 2014 Jul 2;9(7):e101410. doi: 10.1371/journal.pone.0101410. eCollection 2014.

Factors affecting date of implantation, parturition, and den entry estimated from activity and body temperature in free-ranging brown bears.

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Department of Biosciences, Biologicum, Institute of Cell Biology and Neurosciences, Goethe University Frankfurt, Frankfurt/M., Germany.
Department of Forestry and Wildlife Management, Hedmark University College, Campus Evenstad, Elverum, Norway.
Department of Forestry and Wildlife Management, Faculty of Applied Ecology, Agricultural Sciences, Hedmark College, Campus Evenstad, Elverum, Norway; Department of Wildlife, Fish and Environmental Studies, Faculty of Forest Sciences, Swedish University of Agricultural Sciences, Umeå, Sweden.
Département Ecologie, Physiologie et Ethologie, Institut Pluridisciplinaire Hubert Curien, UMR 7178 CNRS/UDS, Strasbourg, France.
Department of Ecology and Natural Resources Management, Norwegian University of Life Sciences, Ås, Norway.
Department of Ecology and Natural Resources Management, Norwegian University of Life Sciences, Ås, Norway; Norwegian Institute of Nature Research, Trondheim, Norway.
Department of Environmental and Health Studies, Faculty of Arts and Science, Telemark University College, Bø i Telemark, Norway; Institute for Wildlife Biology and Game Management, University for Natural Resources and Life Sciences, Vienna, Austria.


Knowledge of factors influencing the timing of reproduction is important for animal conservation and management. Brown bears (Ursus arctos) are able to vary the birth date of their cubs in response to their fat stores, but little information is available about the timing of implantation and parturition in free-ranging brown bears. Body temperature and activity of pregnant brown bears is higher during the gestation period than during the rest of hibernation and drops at parturition. We compared mean daily body temperature and activity levels of pregnant and nonpregnant females during preimplantation, gestation, and lactation. Additionally we tested whether age, litter size, primiparity, environmental conditions, and the start of hibernation influence the timing of parturition. The mean date of implantation was 1 December (SD = 12), the mean date of parturition was 26 January (SD = 12), and the mean duration of the gestation period was 56 days (SD = 2). The body temperature of pregnant females was higher during the gestation and lactation periods than that of nonpregnant bears. The body temperature of pregnant females decreased during the gestation period. Activity recordings were also used to determine the date of parturition. The parturition dates calculated with activity and body temperature data did not differ significantly and were the same in 50% of the females. Older females started hibernation earlier. The start of hibernation was earlier during years with favorable environmental conditions. Dates of parturition were later during years with good environmental conditions which was unexpected. We suggest that free-ranging pregnant brown bears in areas with high levels of human activities at the beginning of the denning period, as in our study area, might prioritize investing energy in early denning than in early parturition during years with favorable environmental conditions, as a strategy to prevent disturbances caused by human.

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