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

• Published in: Ursus (International Association for Bear Research and Management) 2016-01, Vol.27 (2), p.99-109
• Main Authors: Moriwaki, Jun, Shimozuru, Michito, Tsuruga, Hifumi, Mano, Tsutomu, Tsubota, Toshio
• Format: Article
• Language: English
• Subjects: Bears; Black bears; Brown bears; Grizzly bears; Litter size; Ovaries; Ovulation; Parturition; Population Biology; Reproductive history; Yearlings
• ISSN: 1537-6176; 1938-5439
• DOI: 10.2192/URSUS-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 previousyear 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.