Estimating the success rate of ovulation and early litter loss rate in the Japanese black bear (Ursus thibetanus japonicus) by examining the ovaries and uteri

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In order to develop a method for estimating the success/failure rates of reproductiveprocesses, especially those of ovulation and neonate nurturing, in the Japanese black bear(Ursus thibetanus japonicus), we examined offspring status, corpora lutea (CLs), placentalscars (PSs) and corpora albicantia (CAs) in 159 females (0-23 years old) killed as nuisanceson Honshu Island of Japan during 2001-2009. PSs were found to remain in the uterus atleast until November of the year of parturition. CA detectability began to decline afterSeptember of the year of parturition. Monthly and age-specific proportions of CL-presentfemales revealed that the post-mating season starts in August, and that the age of firstovulation is 4 years. These results indicate that the success rate of ovulation (SRO: theprobability that solitary/non-lactating mature females actually succeed in ovulation) can beestimated by calculating the proportion of CL-present females among ≥ 4-year-old femaleswithout PSs captured from August to November; the early litter loss rate (ELLR: theprobability that parenting females lose all of their cubs [0-year-old offspring] before matingseason) can be estimated by calculating the proportion of CL-present females among thosewith PSs and CAs captured in August or later. The estimated values of SRO and ELLR were0.93 (62/67) and 0.27 (6/22), respectively.