How Grizzly Bear Populations are Monitored
Biologists have estimated grizzly bear populations and trends within the Recovery Ecosystems using a variety of methods. The types of methods that are used often depend on resources such as funding, available technology, adequate staffing and characteristics of the study area including observability of bears.
Professional wildlife biologists are constantly trying to improve the accuracy of methods for estimating hard-to-observe species such as grizzlies. Results with higher levels of confidence are obtained when more than one of the following methods is used to estimate abundance or population trend. By using more than one method, biologists can “check” their assumptions and have more confidence in their conclusions. Grizzly bears have slow population growth rates, so a single estimate of growth rate even for a growing population will frequently have a confidence interval that overlaps a range from slightly declining to growing robustly. Similarly, a slightly declining population will yield estimates of growth rate with a confidence interval that overlaps a range from declining to growing.
- Mark-recapture surveys of DNA in hair or in scat samples to estimate population size and, if replicated subsequently, an estimate of population trend in a study area;
- Documenting over time the fate (survival or mortality) of radio-marked bears to estimate population trend;
- Mark-capture-resight surveys of marked individuals to estimate population size or density and, if replicated subsequently, an estimate of population trend;
- Sightings of females with cubs-of-the-year, obtained in a systematic way such as replicated aerial surveys, to obtain an index of population size and, when repeated over a number of years, an estimate of population trend; and
- Capture-recapture sightings obtained using remote-sensing cameras;
To find out more about population estimation methods and the current distribution of grizzly bears, see pages 28-31 in the Grizzly Bear 5-Year Review and the Yellowstone Grizzly Bear Investigation 2014.
The following websites offer more detailed research information for certain Recovery Zones: