Drought, disease, and a bear in your yard

Black bears in California’s Sierra Nevada could come into contact with humans more often as they travel further to find available food, finds a new study in Animal Biotelemetry today. With increasing threats to the bears natural food sources of sugar pine seeds and blue acorns, this could lead to an increase in human-bear incidents and conflict.

By GPS tagging ten different female adult black bears over summer and fall seasons of 2005 and 2006, Rachel Mazur, a wildlife biologist with Sequoia and Kings Canyon National Parks and colleagues were able to match the bears movements with the availability of their favourite foods. They found that when the blue acorn harvest was poor, bears remained in their summer range through fall, matching the distribution of available sugar pine seeds. However, when the blue acorn harvest was good, the bears were tempted into travelling further afield into non-overlapping fall home ranges where they could feast on available high calorie acorns before hibernation.

It was during the days spent travelling between geographically separated home ranges that the bears were most likely to encounter humans. This raises significant conservation concerns as the bears whereabouts becomes less easy to predict by park rangers when there is an increase in blue acorn availability, increasing the chance of conflicts.

In the short term this implies that a decrease in availability of food – specifically blue acorns – would decrease human-bear incidents. But if sugar pine seeds were also depleted, the authors suggest that the bears may be forced to forage across an even wider area in search of food. With a number of worrying pathological, environmental and ecological threats the both sugar pine and oak in Sierra Nevada, bears may need to forage nearer to (your) home to find food. Making the prospect of losing your lunch to a black bear an increasingly likely possibility.

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