A new study seeks to determine if collecting bear hair samples from so-called “rub trees” can provide as reliable a measure of a region’s grizzly bear population as using radio collars.
The effort will be led by Kate Kendall, the U.S. Geological Survey scientist who spearheaded two previous grizzly bear population studies based on genetic analysis of bear hair left when the bruins scratch their backs on trees.
Studies in 1998 and 2000 generated a population estimate for the greater Glacier National Park area, while a 2004 DNA study of bear hair from rub trees produced a population estimate for an 8-million acre area that included Glacier, the Bob Marshall Wilderness Complex and surrounding grizzly bear habitat.
Unlike previous studies, in which bears were drawn to “rub trees” with foul-smelling lure, this study will gather hair samples from known rub trees over three years. The work is an effort to determine if hair samples can provide a reliable measure of whether a region’s grizzly bear population was stable, growing or shrinking.
Kendall’s lead research assistant, Jeff Stetz, explored the statistical modeling for his master’s thesis. Stetz found, on paper, that the work will “reliably detect with a high degree of precision” a minimum 3 percent decline, as well as population increases, within three years.
The field work will test his thesis.
Rub tree samples collected during 2004 detected 53 percent of males and 26 percent of females in about 80 percent of the ecosystem. Rub-tree collections were not conducted on the entire Rocky Mountain Front because of budget constraints.
“In this new study, we feel confident we’ll improve those numbers because there will be an effort to locate rub trees on the East Front,” Kendall said.
The project is expected to cost about $250,000 in the first year, with money coming from grants. That’s well below the $4.8 million cost of the 2004 study, which involved 400 people and included hauling barbed wire and scent lure into wilderness areas. Kendall says the new project will rely on a crew of about 15.
The state Department of Fish, Wildlife and Parks is several years into a study using radio-collared female grizzly bears and monitoring birth and death rates to estimate population trends.
“This is a research project to explore whether we can monitor just using hair collection, as potentially a complement or an alternative to radio telemetry trend monitoring,” Kendall said.