Counts of unique females with cubs in the Apennine brown bear population, 2006-2014

摘要

Brown bears (Ursus arctos marsicanus) in the Apennines, central Italy, survive in a precarious conservation status but the reproductive performance of the population has never been formally assessed. Each year, from 2006 to 2014, we conducted surveys of females with cubs (FWC) to estimate the minimum number of female bears that reproduced and annual productivity in this bear population. We discriminated unique family groUps based on simultaneity of sightings, presence of individually recognizable bears, and ad hoc distance-based rules developed using Global Positioning System relocations from 11 adult female bears in our study population. To estimate the due number of FWC from unique counts, we applied 2 estimators (Chao2, Capwire) known to handle heterogeneity in sighting probabilities relatively well at small sample sizes. Annually, we estimated 1-6 ((x) over bar = 3.9 +/- 1.5 SD) unique FWC and tallied a minimum of 3-11 ((x) over bar = 7.4 +/- 3.0 SD) cubs in the population. No temporal trend in FWC was observed and the mean estimate of reproductive females corresponded well with an independent estimate of total population size obtained in 2011. Although we confirmed that the population is still reproductively functional, the small number of reproducing females and their year-to-year fluctuations dramatically underlined the precarious status of Apennine bears. We concur with previous authors that counts of unique FWC are an effective means to assess reproductive output in small bear populations, although it is advisable that more in-depth demographic studies complement this technique.