Friebe Andrea, Evans Alina L, Arnemo Jon M, Blanc Stéphane, Brunberg Sven, Fleissner Günther, Swenson Jon E, Zedrosser Andreas
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.
PLoS One. 2014 Jul 2;9(7):e101410. doi: 10.1371/journal.pone.0101410. eCollection 2014.
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.
了解影响繁殖时间的因素对于动物保护和管理至关重要。棕熊（ Ursus arctos）能够根据自身脂肪储备来改变幼崽的出生日期，但关于自由放养棕熊的着床和分娩时间的信息却很少。怀孕棕熊在妊娠期的体温和活动水平高于冬眠的其他时期，并在分娩时下降。我们比较了怀孕和未怀孕雌性在着床前、妊娠期和哺乳期的平均每日体温和活动水平。此外，我们还测试了年龄、窝仔数、初产情况、环境条件和冬眠开始时间是否会影响分娩时间。着床的平均日期为12月1日（标准差 = 12），分娩的平均日期为1月26日（标准差 = 12），妊娠期的平均持续时间为56天（标准差 = 2）。怀孕雌性在妊娠期和哺乳期的体温高于未怀孕的熊。怀孕雌性的体温在妊娠期会下降。活动记录也被用于确定分娩日期。通过活动和体温数据计算出的分娩日期没有显著差异，50% 的雌性两者相同。年龄较大的雌性更早开始冬眠。在环境条件有利的年份，冬眠开始得更早。在环境条件良好的年份，分娩日期较晚，这是出乎意料的。我们认为，在筑巢期开始时人类活动水平较高的地区，如我们的研究区域，自由放养的怀孕棕熊在环境条件有利的年份，可能会优先将能量投入到早期筑巢而不是早期分娩上，以此作为防止人类干扰的一种策略。
