Abstract 228 – Verification of the relationship between testosterone and behavioral changes in male Asian black bear (Ursus thibetanus)

Naoki Takekoshi, Jumpei Tomiyasu, Yojiro Yanagawa, Naoki Ohnishi, Tomoko
Naganuma, Seungyun Baek, Miu Itoh, Tatsuhito Nishiwaki, Chinatsu Kozakai, Shinsuke Koike,
Koji Yamazaki

Sexual hormones play a crucial role in reproductive behavior of mammals. Testosterone, a type
of sexual hormone in males, exhibited closely linked to competition among males for access to
female in previous study, which applied direct observation and fecal samples containing
testosterone metabolites. In case of the Asian black bear (Ursus thibetanus), males typically
approach females and remain in proximity in a small area. While direct observation allows for
accurate behavior recording, it is difficult to keep observing over extended periods. In this
study, we investigated fecal testosterone metabolites (FTM) and behavior with global
positioning system (GPS) collar of Asian black bears, to clarify the potential role of sexual
hormones as behavioral factors for male bears. We hypothesized that FTM concentration in
male bears would increase with (1) longer movement distance to encounter more females, or
(2) shorter movement distance to ensure mating with limited females. We fitted GPS collars to
males for calculating their daily distances. For collecting fresh feces for FTM assay, we targeted
sample collection based on cluster of GPS points received via satellite in semi real-time. We
gained GPS points from 5 males and collected a total of 297 feces from 2022 to 2023. FTM had
temporary high concentration, mainly during the reproductive season (May-July), although
some male bears elevated concentrations after the reproductive season (August-October). The
movement distance was negatively related to FTM concentration but those were not significant
in reproductive season. These findings do not exhibit the tendency clearly, but may seem that
testosterone level rise when male bears engage courtship behaviors with females. This study
provides the first insight of the relationship between movement distance and testosterone
levels for males through bear active season.