Estimating the seasonal energy balance in Asian black bears and associated factors

Abstract

Energy balance (i.e., energy intake minus energy expenditure) is an essential factor when evaluating an animal's nutritional state. We aimed to identify periods of the year that are most important for Asian black bears (Ursus thibetanus) in terms of energy balance. We estimated bears’ daily energy balance by estimating energy intake based on the energy content (kcal/g) of major food items, their average ingestion rate (g/min), and daily feeding time (min) and by estimating energy expenditure using an equation for the costs of resting, traveling, and feeding based on behavioral data of 34 bears fitted with GPS collars in central Japan. Because food habits of bears change seasonally, we estimated daily energy balance for each month. And, because bears change their feeding behavior depending on the availability of hard mast, we made separate estimations for years of good and poor mast conditions during autumn. We identified major food items from fecal analysis and calculated the gross energy content per unit for each item. Based on direct observation of bears feeding over 10 yr, we measured ingestion rates of the major food items; Quercus crispula acorns on the tree had the highest ingestion rate, whereas the values of other items did not show notable characteristics. The variability of energy expenditure rose moderately in good mast years, except for males. On the other hand, there was a bimodal pattern of energy intake and energy balance, declining from May to July, rising again from August to October, and declining in November. The peak of energy intake and energy balance was larger in good mast years than in poor mast years only for females, whereas the cumulative energy balance in good mast years was larger than in poor mast years for both sexes. After poor mast years, the cumulative energy balance of males becomes negative in February, during hibernation, and did not exceed zero until August, even if they could start feeding in May. Thus, further longitudinal studies that examine cumulative energy balance, rather than energy balance alone, are necessary to clarify the seasonal change in the nutritional state of Asian black bears.

Animal‐borne video systems provide insight into the reproductive behavior of the Asian black bear

“…The energy balance is an essential factor to evaluate the nutritional state of bears (Robbins et al., 2004). The energy balance of Asian black bears has previously been suggested to follow a seasonal, bimodal pattern, dropping from spring to summer and increasing from summer to a peak in autumn (Furusaka et al., 2019). In particular, decreased food consumption by Asian black bears in summer (i.e., June and July) was associated with a large decrease in their energy balance.…”

“…In particular, decreased food consumption by Asian black bears in summer (i.e., June and July) was associated with a large decrease in their energy balance. One factor that has been proposed to explain this is low availability of food resources during this time of the year (Fuchs et al., 2019; Furusaka et al., 2019). However, our results suggest that within this period, bears decreased foraging activities on social days compared with solitary days, which accounted for about half of the days in the mating season in one male and both females.…”

Functional dietary response of Asian black bears to changes in sika deer density

“…Interannual differences in the consumption of hard mast are due to the annual fluctuation of mast production (Koike et al 2012, Naganuma et al 2020). In general, Asian black bears seem to follow an energy‐conserving strategy during the hyperphagia by eating large amounts of hard mast with high carbohydrate content (i.e., a food source that is relatively predictable in time and space) rather than searching for deer carcasses, which requires extensive travel time (Furusaka et al 2019). Although our models are unable to directly compare deer consumption between seasons, bears may reduce deer consumption from the deer birthing season to the rutting season because of this strategy (Table 1; Figure 4).…”

Geographic distributions shape the functional traits in a large mammalian family

“…We required estimates of the dietary proportion of mass that bears consumed to calculate macronutrient compositions. Therefore, studies where foods were originally reported as the proportion of dry mass of diet or were estimable after applying fecal correction factors (CFs) to percent fecal volume or dry weight estimates were included (Baldwin & Bender, 2009 ; Bojarska & Selva, 2012 ; Furusaka et al., 2019 ; Hewitt & Robbins, 1996 ). We excluded studies where diet composition was assessed in ways other than percent fecal volume and dry mass.…”