Brown Bears

A brown bear, or grizzly bear, seen on an aerial survey in Bering Land Bridge National Preserve.

Dylan Schertz/NPS

The brown bear is an iconic species of Alaska’s national parks, and its presence symbolizes the wilderness character of these vast landscapes. Alaska has more than 50% of the remaining North American brown bears and the second largest population worldwide. In spite of the vast habitat protection provided by Alaska’s national parks and regulated harvest, the vulnerability of brown bear populations to human-caused disturbance is high and their resilience to disturbance is minimal. This sensitivity makes them good indicators of ecosystem integrity; a declining bear population can be an early indicator of landscape-level changes. Increasing demands for oil, gas, coal, and minerals along with accompanying industrial development on adjacent lands may pose a threat to brown bear populations through habitat fragmentation and human-caused mortality. Parks in the Arctic Inventory and Monitoring Network (ARCN) may ultimately provide a refuge for brown bears in northwest Alaska that are adapted to life in the Arctic, but strong monitoring programs are needed to understand whether these bear populations can remain healthy in a rapidly changing Arctic.

We monitor brown bears in all the Arctic parks specifically to understand:

• Long-term trends in bear abundance and density within 5 park units

• Long-term trends in bear occupancy in each survey area
  

How we monitor brown bears

The ARCN brown bear monitoring program surveys four study areas, on a rotating schedule—each area is sampled once every five years during late May and early June. Our biologists use a novel technique to estimate the number and distribution of bears living in ARCN parks. The method, called “photo mark-resight”, requires two teams, each consisting of an aircraft pilot and observer, to search for bears in a survey unit. After each team surveys a unit, they swap and re-survey the other team’s unit. When they see a bear or bear group, they take pictures and record a location. At the end of the day, the biologists use the photos and locations to determine which bear groups were seen by both survey teams. We do not see 100% of the bears present during a survey, but re-sampling units enables us to estimate the number of undetected bears in an area. To compare among survey areas of different sizes, the abundance estimates are converted to bear density estimates (Schmidt et al. 2021).

Contact: Zackary Delisle

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