Factors Affecting Date of Implantation, Parturition, and Den Entry Estimated from Activity and Body Temperature in Free-Ranging Brown Bears

Abstract

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.

Challenges of measuring body temperatures of free-ranging birds and mammals

“…Sedation itself is often unproblematic, but mortality may occur despite proper dosage [38] so care must be taken to monitor vital signs and provide post-surgical recovery. Although surgical implantation is logistically demanding, it has been successfully used on wild animals by either transporting animals to temporary surgical facility [39] or directly undertaking surgery in the field [40]. Implantation of devices may actually be preferable to externally attached loggers in long-term studies [41].…”

“…Implanted data loggers are, therefore, particularly suited to long-term deployments. Examples of these include studies on thermoregulation [42,43], circadian rhythms [39,[46][47][48], hibernation and torpor [40,49,50], temperature change during diving and foraging [43,51,52], incubation [53], egg laying in monotremes [54] and comparison between wild and captive species [47,55]. One disadvantage with data loggers is that animals must normally be recaptured for data retrieval, which can be difficult or even impossible for some species.…”

Short-term effects of tagging on activity and movement patterns of Eurasian beavers (Castor fiber)

“…Cooke et al 2011;Kays et al 2015). These tags can be equipped with a suite of sensors related to animal state, such as heart beat frequency and/or body temperature (Butler et al 2004;Evans et al 2016;Friebe et al 2014), but may also document movement patterns (Rhodes et al 2005;Zimmermann et al 2007), general activity, behaviour and proxies for energy expenditure (Shepard et al 2008;. Such tags can be used under challenging environmental conditions, including aquatic (Gleiss et al 2011;Thorrold et al 2014) and terrestrial habitats (Steyaert et al 2014;Williams et al 2014), as well as on species that spend a considerable amount of their time in air (Nathan et al 2012;Spiegel et al 2015).…”

Six Years in the Life of a Mother Bear - The Longest Continuous Heart Rate Recordings from a Free-Ranging Mammal

“…This finding points to the value of HR and activity monitoring for perceiving effects of short-term and long-term effects of climate change. With warming trends, we might expect to see later denning, earlier den emergence and possibly earlier parturition to enable cubs to leave the den earlier, and more pulses of activity in mid-winter due to unusually warm weather and melting snow282930.…”