Assessment of key reproductive traits in the Apennine brown bear population

Although knowledge of reproductive parameters is critical to project the probability of persistence of small and endangered populations, no such data are available for the relict Apennine brown bear (Ursus arctos marsicanus) population (central Italy). From 2005 through 2014, we compiled re-sight data on marked adult female bears (3 <= n <= 10/yr, for 78 total bear-years) and unmarked, distinct family groups (a = 17) to estimate basic reproductive traits in Apennine bears. We had a high rate of radiocollar failure, so we included in our sample marked, adult female bears with non-functioning radiocollars and used multi-event models in a capture recapture, robust-design framework to correct for their incomplete detection and potential classification error. We obtained annual detection probabilities of 0.77 and 0.82 for reproductive and non-reproductive female bears, respectively, and the classification error of their reproductive state was negligible (P = 0.003). Mean litter size was 1.9 (+/- 0.7 SD) cubs, weaning occurred at approximately 1.4 years, and the interbirth interval was 3.7 years. Based on our multi-event model, female bears had highest probability to reproduce 3-4 years after their last reproduction, and their average reproductive rate was 0.243 (95% CI = 0.072-0.594). Average survival of adult female bears was 0.93 (95% CI = 0.83-0.97) whereas apparent cub survival was 0.49, based on the proportion of cubs seen before weaning the year following birth. Our findings place reproductive parameters of the Apennine bear population at the lower bound along the spectrum reported for other non-hunted brown bear populations. Coupled with high levels of human-caused mortality, a relatively low reproductive performance may explain why Apennine bears have not expanded their range beyond their historical minimum. More in-depth demographic investigations are urgently needed to corroborate our results and to assess the relative role of density-dependence versus inbreeding depression in affecting the dynamics of this imperiled bear population.