A preliminary estimate of the Apennine brown bear population size based on hair-snag sampling and multiple data source mark-recapture Huggins models

Although the brown bear (Ursus arctos) population in Abruzzo (central Apennines,Italy) suffered high mortality during the past 30 years and is potentially at high risk ofextinction, no formal estimate of its abundance has been attempted. In 2004, the Italian ForestService and Abruzzo National Park applied DNA-based techniques to hair-snag samples fromthe Apennine bear population. Even though sampling and theoretical limitations preventedestimating population size from being the objective of these first applications, we extracted themost we could out of the 2004 data to produce the first estimate of population size. Toovercome the limitations of the sampling strategies (systematic grid, opportunistic sampling atbuckthorn [Rhamnus alpina] patches, incidental sampling during other field activities), we used amultiple data-source approach and Huggins closed models implemented in program MARK.To account for model uncertainty, we averaged plausible models using Akaike weights andestimated an unconditional population size of 43 bears (95% CI 5 35-67). We urge caution ininterpreting these results because other expected but undefined sources of heterogeneity (i.e.,gender) may have biased this estimate. The low capture probability obtained through thesystematic grid prevented the use of this sampling technique as a stand-alone tool to estimate theApennine bear population size. Therefore, further applications in this direction will require asubstantial improvement of field procedures, the use of a multiple data-source approach, orboth. In this perspective, we used Monte Carlo simulations to compare the relative performanceof the 3 sampling approaches and discuss their feasibility to overcome the problem of small andsparse DNA data that often prevent reliable capture-mark-recapture applications in small bearpopulations.