"Viruses mutate faster than anything we know," Biek said, adding that this makes them easier to study over short time periods.
Cougar genes change very slowly, Biek added, so genetic testing cannot yield much information about the cats.
Using the virus as a tracking device, however, enabled Biek's team to establish when and where cougar populations began to rebound.
The researchers were also able to look at how far the cats had traveled across the far-flung territory of the Rocky Mountains over the past 80 years.
Paul Beier, professor of conservation biology at Northern Arizona University in Flagstaff, said using virus research in combination with radio collars and gene-flow studies may help scientists track cat movements over longer periods of time.
"It takes a long time to see patterns, and this may help integrate longer-term gene flow and short-term information from radio collars," he said.
The Importance of Tracking
Knowing how and where cougars travel and thrive is important to maintaining a healthy cougar population, experts say.
Toni Ruth, a conservation scientist with the Wildlife Conservation Society who studies cougars, noted that identifying the cats' movement patterns can help conservationists identify the corridors they frequently travel.
"For conservation purposes, if we understand how they are getting from one area to another we can maintain the natural corridors they follow," Ruth said.
Wildlife corridors are natural pathways animals use, unimpeded by barriers such as highways and human developments, to migrate, hunt, or seek mates.
In recent years, many scientists have promoted the conservation of such corridors as a critical tool for the survival of large mammals.
"The more we understand of flows across landscapes the more we understand what we are trying to conserve in terms of habitat," Northern Arizona University's Beier said. "It also helps us understand when there is a loss of flow."
Knowing which pathways cougars take, Ruth added, may also help people plan for and minimize conflicts between humans and the big cats.
Not Just for Cougars
Biek noted that his team's virus-tracking method can be used in other species known to carry viruses.
Most species of big cats carry some form of FIV, which may allow researchers to replicate similar research on other cat species.
Likewise, he said, primates carry a virus similar to FIV that scientists can test for to track their movements.
Ruth added that virus analysis has advantages over traditional tracking methods, like the use of radio collars.
"Once they move out of our population it is difficult to keep up with the signal," Ruth said, of the cougar cubs she has tried to track with radio collars.
"We fly 200 miles [320 kilometers] from their natal area, and sometimes we still can't find them."
Another advantage is that, unlike radio signals, virus information carries history, Ruth adds. With this information scientists are able to see not just where the animals went today but where they came from decades ago.
"The whole thing is novel and fascinating," she said.
Free E-Mail News Updates
Sign up for our Inside National Geographic newsletter. Every two weeks we'll send you our top stories and pictures (see sample).
SOURCES AND RELATED WEB SITES