Female Andean bears select rugged den sites in the tropical dry forest

Maternal dens are critical for bear reproduction. Unfortunately, we know almost nothing about how Andean bear females select and use the dens or den sites where they give birth and raise young cubs. Because food is available year-round where they live, Andean bears are active year-round. This may liberate Andean bear females from constraints faced by some female American black bears and brown bears, who may spend months inactive in dens.

To evaluate what might influence which dens and den sites were used by female Andean bears, we worked in partnership with the Spectacled Bear Conservation Society and measured many characteristics of maternal dens and den sites in the tropical dry forest of NW Peru.

Adult Andean bears there do not face many threats, except for humans, but newborn cubs might be vulnerable to temperature extremes or to predation by puma. So, we expected that female Andean bears might use dens with fewer or smaller openings than other available cavities. We also thought that perhaps female Andean bears would use den sites that were closer to water or food, or farther away from human activity, or on steeper slopes, or in more rugged areas.

There are no trees in the dry forest that are large enough to have hollow trunks suitable for a bear den. So, all dens that female bears used were cavities below or between large boulders. It appears as though females did not select dens with any particular characteristics. Some dens had small entrances, while others had large entrances; some dens had resting chambers just barely big enough for a female to lie in, while other dens had grand chambers large enough for multiple adult bears.

Female Andean bears also did not appear to select den sites based on their distance to water or food, or human activity, or elevation. Females did, however, appear to select den sites that were on unusually steep and rugged slopes. At those sites it would be more difficult for humans and other large mammals, such as pumas, to walk. This may protect young bear cubs from disturbance and this may also explain why it has been so hard for researchers to find maternal dens of Andean bears!

Although it may be hard for researchers to find these dens, the variables that appear to influence the use of den sites can be evaluated remotely from digital maps. So, conservation planners can model where maternal den sites might be found and they can plan to minimize human activity in sites where Andean bear females may be rearing their newborn cubs.    

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