Estimation of reproductive parameters and their annual variation in brown bears of Hokkaido, Japan

• Published in: Ursus (International Association for Bear Research and Management) 2017-01, Vol.27 (2), p.99-109
• Main Authors: Moriwaki, Jun, Shimozuru, Michito, Tsuruga, Hifumi, Mano, Tsutomu, Tsubota, Toshio
• Format: Article
• Language: English
• Subjects: corpora lutea; Hokkaido brown bear; implantation rate; litter size; ovulation rate; placental scars; reproduction interval; reproductive parameters; reproductive tracts; Research s; Ursus arctos
• ISSN: 1537-6176; 1938-5439
• DOI: 10.2192/URSU-D-16-00005.1

The reproductive tracts of 130 adult female brown bears (Ursus arctos) in Hokkaido, Japan, euthanized during 2010–2013 for conflict management, were examined for the presence and number of corpora lutea (CL) in the ovary and placental scars (PS) in the uterine horns. We scored PS on a 0–5 scale based on morphological features including their rim and color. They were characterized as representing either current-year parturition, as determined by accompanying cubs, or previous-year parturition, as determined by accompanying yearlings. In total, 128 females were divided into 3 reproductive categories: 44 females with current-year parturition, 39 with previous-year parturition, and 45 solitary females that had not given birth for >2 years. The estimated ovulation rate was 2.21 ± 0.55 (mean ± SD), the implantation rate was 1.91 ± 0.74, and the litter size was 1.54 ± 0.51. Implantation rates were lower than ovulation rates and changed annually during 2010–2013. Systematic observation of PS and CL allowed us to evaluate the reproductive history and parameters in Hokkaido brown bears and ascertain their annual variation.