Setting up a bear baseline

Wild black bear cub.

NPS photo.

In the late 1960s, park managers thought that as few as 50 black bears might roam within the Park. At that time, no one guessed that dozens of bears lived a quiet life in the wild for every one that caused trouble with visitors. To eventually come to this conclusion, Dr. Pelton and his students—including van Manen, who was a graduate student in the early 1990s and then full time research ecologist, had to start with a baseline study.

The first step of the baseline was estimating the population. Counting bears was never easy—bears are secretive and active when people aren’t—but researchers adapted their methods over the years. Live trapping of bears took place for 8 weeks each summer and has provided the basis for the long-term study through 2006. When researchers trap bears, they use different methods to track them. These methods changed considerably over time:

 

• Radio isotopes—In the early 1970s, researchers tagged bears with harmless, lightly radioactive materials (isotopes) that they could detect in the bear’s scat. This was an early type of mark-recapture, so they could tell if the bear had been caught before or if they could count it as a new animal, using the ratios of marked vs. unmarked bears to estimate the population.
• Tagging—Similar to radio isotopes, this method involved giving a bear an “earring,” an identification tag with a number in its ear.

 

Wildlife managers and researchers fit captured bears with radio telemetry collars, as in this 1997 photo.

NPS photo.

Both of these methods provided researchers with an estimate of the total number of bears in the national park, which was around 600 bears in the early 1970s. They witnessed substantial population growth during the early to late 1990s, and now that number is closer to 1600 bears. These methods didn’t give them any information about overall bear home ranges, habitat use, diet, and reproduction, however. To find these answers, which would help wildlife managers make long-term decisions, they continued the baseline study with this technique:

• Radio telemetry—This type of work was relatively new when the black bear study started. Bear researchers in Yellowstone National Park were some of the first to use radio collars to track large animal—mainly grizzly bear—movements. Researchers in the Smokies used similar techniques. Radio collars were huge, weighty yokes in the early days. They have improved over time and provided extremely valuable information regarding movement and activity patterns, home ranges, habitat use, and winter denning sites.

 

In addition, researchers developed techniques based on information from the long-term study that managers can use to monitor the bear population and their food resources:

• Bait station surveys—One of the initial goals of the bear research was to develop a population monitoring technique. In 1981, Great Smoky Mountains National Park adopted the bait station technique as the main monitoring method, one we still use today. Managers hang sardine cans every ½ mile along transects—mapped lines in the forest—and monitor which ones bears visit. The total number of sites “hit” (the number of cans chewed/licked clean) shows researchers where the bear population is distributed, and how this distribution changes from year to year. This method takes less time that others, can be done all over the Park, and doesn’t have a big impact on the habitat, bears, or humans involved. While not exact, the population information this technique gives can show large-scale population changes over time and space.
• Mast surveys—Each year, wildlife managers at the Park estimate how much hard mast (acorns, hickory nuts) and soft mast (berries, wild grapes) are available for bears. Collecting these data in conjunction with bear population studies tells us how the bear population responds to different amounts of hard or soft food supplies, and allows managers to plan ahead.
• DNA collection—Over the last decade, researchers have been able to study a large number of individual bears using a genetic type of mark-recapture study. Bears have to shimmy under a low barbed wire to reach bait, leaving behind hair tufts. Researchers extract DNA from the hair, and can recognize individuals, map where they occur within the Park, and track how the genetic structure of the population may change due to changes in the landscape (roads, housing development, etc).

 

The bait station, mast surveys, and DNA collection are good ways to study populations, van Manen explained, because they provide detailed information at different scales—from the entire population to individuals—but they don’t require capturing animals to understand Park-wide trends. The DNA collection and analysis provides the best information but a large obstacle to this form of research is cost. As a result, the Park has not yet switched to this type of population monitoring.

Field Trip Earth offers an in-depth look at what University of Tennessee field research on black bears entails. Go to their site to read about graduate student researchers and watch podcasts of a bear work-up. Click the back arrows to return to this page.

Return to Dispatches from the Field: Issue 3.