We are pleased to share these recent URSUS articles with you. The articles below are open access and can also be accessed through your IBA membership account link to BioOne.
Possible sexually selected infanticide by polar bears in western Hudson Bay
David McGeachy, Nicholas J. Lunn, Andrew E. Derocher
Ursus 2024 (35e20), 1-11, (29 October 2024) https://doi.org/10.2192/URSUS-D-23-00028
KEYWORDS: climate change, Hudson Bay, intraspecific competition, polar bears, sex ratio, sexually selected infanticide, sexual selection, Ursus maritimus
Open Access Article
Infanticide occurs in a diversity of taxa and may provide benefits to the perpetrator through nutritional gain, reduced competition, or increased fitness from mating opportunities through sexually selected infanticide (SSI). Infanticide, however, is rarely observed. We documented a probable infanticide event by a 23-year-old adult male polar bear (Ursus maritimus) on a 3-month-old cub in western Hudson Bay, Canada, during the spring of 2023. We subsequently documented a 21-year-old solitary female who was lactating and in breeding condition with swollen labia, suggesting polar bears return to estrous quickly in the absence of cubs. Using the literature, we examined the relationships among polar bear cub-of-the-year, adult male survival, and the ratio of male/female mortality. We suggest SSI as the plausible explanation for the infanticide event observed and discuss how indirect effects from climate change may affect the prevalence of infanticide as a mechanism regulating polar bear populations.
Factors affecting body weight fluctuation in free-ranging Asian black bears
Naoki Takekoshi, Akina Fujitani, Naoki Ohnishi, Chinatsu Kozakai, Shinsuke Koike, Koji Yamazaki
Ursus 2024 (35e21), 1-12, (4 November 2024) https://doi.org/10.2192/URSUS-D-23-00026
KEYWORDS: age class, behavioral factor, demographic group, Energy budget, Japan, noninvasive body weighing system, nutritional condition, Ursus thibetanus
Open Access Article
The Asian black bear (Ursus thibetanus) shows seasonal changes in body weight, activity level, and range use. However, there is little information available on these factors in individuals in the wild. We documented the body weights of free-ranging Asian black bears from spring to autumn, 2017 to 2019, in the Nikko-Ashio Mountains, Tochigi Prefecture, Japan, by using a newly noninvasive body weighing system (NIBWS) that we developed. We also fitted Asian black bears with global positioning system (GPS) collars with built-in activity sensors to evaluate the relationship between body weight, behavioral factor, and activity level. Bears visited the NIBWS 88 times in 2017, 176 times in 2018, and 321 times in 2019. We recorded the body weights of 4 bears in 2017, 15 bears in 2018, and 11 bears in 2019. Specifically, we consecutively recorded the body weight of an adult female from 2017 to 2019 and collected GPS location data from 2017 to 2018. The adult female was solitary in 2017, and she was accompanied by 2 cubs in 2018 and the yearlings of those cubs in 2019. Her body weight was lowest in 2018, likely because she had spent a large amount of her energy expenditure on nursing her cubs, compared with the year when she was solitary or nursing her yearlings. The GPS data showed that no significant relationship was found between body weight and any behavioral factors. Although her activity level decreased drastically in late August, her body weight did not decrease accordingly. In contrast, a subadult female that we tracked in 2019 increased her body weight during May to August, likely because she was solitary and required high intake of energy and nutrition for growth. Although our results provide only a snapshot, we established NIBWS and this is the first record of body weight changes over multiple years in free-ranging Asian black bears to our knowledge.