Site characteristics influence Andean bear natal-den selection in dry forest habitat

Abstract

Natal dens are critical for reproduction in bears, yet we know virtually nothing of Andean bear (Tremarctos ornatus) denning ecology, nor whether female Andean bears select dens or den sites with specific characteristics. We analyzed data from 2008 to 2013 on characteristics of 8 natal dens (shelter and surroundings within 5 m) and den sites (context at ≥50 m from den) used by 4–5 females, with 21 potential (suitable but unused) natal dens and 30 potential den sites in the equatorial dry forest of Cerro Venado, Lambayeque, Peru. All observed natal dens were preexisting cavities under rocks, <5 m from a cliff. Natal dens had 1–2 entrances that varied in diameter (mean ± SE = 66.3 ± 9.01 cm). Maximum resting dimension within these dens was >2 m (242.3 ± 32.97 cm) and minimum vertical height within the resting area was <1.5 m (71.0 ± 10.93 cm). We found no evidence that female Andean bears preferred natal dens with any of the measured characteristics. Thus, if females in this area are selective when seeking a natal den, they are selective based on den site characteristics. All natal den sites were <50 m from a cliff and at relatively high elevations for this study area (887.8 ± 73.73 m above sea level). Sites were relatively steep (37.4 ± 6.38°), rugged (168.4 ± 26.29), and not obviously close to water (0.9 ± 0.21 km). Variables based on elevation and slope best described female use of natal den sites. Food, water, and solar heating seemed not to affect use of sites. Our results suggest that topographic resistance to travel by humans and other large mammals affects natal den site use in this area, and possibly elsewhere. The relevant topographical characteristics can be evaluated remotely, so conservation planners can model where natal den sites may occur in other habitats.