Reproductive parameters and cub survival of brown bears in the Rusha area of the Shiretoko Peninsula, Hokkaido, Japan

Abstract

Knowing the reproductive characteristics of a species is essential for the appropriate conservation and management of wildlife. In this study, we investigated the demographic parameters, including age of primiparity, litter size, inter-birth interval, reproductive rate, and cub survival rate, of Hokkaido brown bears (Ursus arctos yesoensis) in the Rusha area on the Shiretoko Peninsula, Hokkaido, Japan, based on a long-term, individual-based monitoring survey. A total of 15 philopatric females were observed nearly every year from 2006 to 2016, and these observations were used to estimate reproductive parameters. The mean age of primiparity was 5.3 ± 0.2 (SE) years (n = 7, 95% CI = 5.0–5.6). We observed 81 cubs in 46 litters from 15 bears. Litter size ranged from one to three cubs, and averaged 1.76 ± 0.08 (SE) cubs/litter (95% CI = 1.61–1.91). Inter-birth intervals ranged from 1 to 4 years, and the mean value was estimated as 2.43 (95% CI = 2.16–2.76) and 2.53 (95% CI = 2.26–2.85) years in all litters and in litters that survived at least their first year, respectively. The reproductive rate was estimated from 0.70 to 0.76 young born/year/reproductive adult female, depending on the method of calculation. The cub survival rate between 0.5 and 1.5 years ranged from 60 to 73%. Most cub disappearances occurred in July and August, suggesting that cub mortality is mainly due to poor nutrition in the summer. All reproductive parameters observed in the Rusha area on the Shiretoko Peninsula fell within the range reported in Europe and North America, and were among the lowest or shortest age of primiparity, litter size, and inter-birth intervals, and ranked at a high level for reproductive rate.

Density and reproductive characteristics of female brown bears in the Cantabrian Mountains, NW Spain

“…Similar values of litter size have been recorded, e.g. in Banff National Park and Kananaskis Country (Alberta: 1.8 cubs, Garshelis et al 2005), the Mackenzie Mountains (Canada: 1.8 cubs, Steyaert et al 2012), Banff-Kanan, (Canada: 1.8 cubs, Steyaert et al 2012), Hokkaido (Japan: 1.6-1.8 cubs, Mano & Tsubota 2002;Shimozuru et al 2017;and 1.5 cubs, Moriwaki et al 2017) and the Swan Mountains (USA: 1.6 cubs, Steyaert et al 2012). It is worth noting here the similarity in reproductive traits between the Cantabrian population and another small and isolated population in southern Europe, the Apennine brown bear population in Central Italy (Tosoni et al 2017).…”

“…However, the small litter size of Cantabrian bears is compensated by short mean litter intervals (as is typical of European and Japanese bear populations; Frkovic et al 2001;Dahle & Swenson 2003b;Steyaert et al 2012;Shimozuru et al 2017), which results in a relatively high population reproductive rate (0.7) compared to bear populations from other parts of Europe, Asia and North America (Garshelis et al 2005;Steyaert et al 2012;Shimozuru et al 2017). The estimated reproductive rate for the Cantabrian population is among the highest recorded for brown bears (i.e.…”

“…FCOY were videorecorded and photographed from multiple angles every year as they emerged from their dens with cubs, which allowed comparison with images of previous years to establish the mothers' identity. Indeed, individual patterns of colours and markings do not change seasonally or even year to year, and thus can be used as the most definitive factor in the identification of individual bears (Palomero et al 2007;Shimozuru et al 2017). As in Shimozuru et al (2017), chest markings and colour variations were the main elements used in identifying individuals.…”

“…Indeed, individual patterns of colours and markings do not change seasonally or even year to year, and thus can be used as the most definitive factor in the identification of individual bears (Palomero et al 2007;Shimozuru et al 2017). As in Shimozuru et al (2017), chest markings and colour variations were the main elements used in identifying individuals. The colour patterns of mothers also allowed estimating reproductive parameters of focal females (see Estimation of reproductive parameters).…”

“…mean number of cubs per litter) was determined immediately after den exit and, when possible, checked each time the same FCOY was observed from den exit to the following den entry (Wielgus & Bunnell 2000). However, because of the lower visibility of FCOY in our study area when families leave the surroundings of the dens (Penteriani et al submitted), our data do not always account for those cubs that died later in the season (Wielgus & Bunnell 2000;Shimozuru et al 2017). It is noteworthy that the litter sizes estimated at den emergence are higher because some cubs may die in subsequent months.…”