Long-term survival of Colo. lynx still uncertain

A Colorado Division of Wildllfe map included in the annual 2009 lynx report shows higher levels of lynx activity in red, including parts of Summit County. Click on the image for a larger view.

Wildlife biologists say they just aren’t sure if the population will be able to keep pace with mortality. More than 25 percent of documented lynx deaths are related to human activity, including poaching and vehicle collisions.

By Bob Berwyn

SUMMIT COUNTY — Despite ongoing intensive efforts to monitor Colorado’s reintroduced lynx population, biologists are still not sure if the threatened cats will survive in the long run.

“It’s not clear if reproduction will keep up with mortality,” said Kurt Broderdorp, the Grand Junction-based biologist who keeps tabs on lynx for the U.S. Fish and Wildlife Service.

The lynx reintroduction program was led by the Colorado Division of Wildlife, with cooperation from other agencies, but Broderdorp is a key player because the Fish and Wildlife Service is responsible for animals — like lynx — on the endangered species list.

“We continue to have mortality … and those losses aren’t helping the lynx population. How many can you lose before you start losing ground?” Broderdorp said.

Recent maps published by the state wildlife agency show that the powder-loving cats have spread far from the release area, with intensive activity in parts of Summit County, especially ranging north and west from Breckenridge toward Copper Mountain and Vail Pass.

Also in question is whether state biologists will be able to accurately count lynx in the future. Using small planes, satellites and on-the-ground tracking crews is labor intensive and expensive. With the state budget crunch, it’s not clear whether the Division of Wildlife will have the resources to continue those efforts.

In a news release last month, leaders of the lynx program indicated they may switch to a more theoretical approach, based on computer modeling. Automated motion-sensor cameras and other ground-based methods could be used to augment the models, the Division of Wildlife said in the 2009 annual lynx report.

Between 1999 and 2006, state biologists transplanted 218 lynx from Alaska and Canada to the San Juans. Since then, researchers have documented 118 lynx deaths, with more than a quarter of those fatalities related to human involvement, including poaching and vehicle collisions.

Trackers and biologists have also documented the birth of about 115 lynx kittens dating back to 2003. In 2007 and 2008, they couldn’t find any sign of lynx reproduction, but the researchers believe that other kittens have been born to females that can’t be tracked because they don’t have active radio transmission collars.

In 2009, 10 kittens were born, including the first documented set of third-generation Colorado kittens, born to native Colorado lynx. State biologists said this was a key step toward establishing a self-sustaining population.

Monitoring lynx involves a mix of old-fashioned tracking and high-tech satellite and computer technology. Almost all the lynx released since 1999 were fitted with dual satellite/VHF radio collars, with the satellite components programmed to be active for 12 hours per week.

The active periods for individual collars are staggered throughout the week. The signals from the collars enables Argos, NASA and NOAA satellites to track the animals, with the location information relayed to state biologists via e-mail.

Once the general location is established, ground-based trackers on snowshoes and skis can move in and examine dens, evaluate the type of habitat the cats are using and even determine what they are eating.

That’s crucial, because lynx populations are closely tied to the availability of snowshoe hares. The absence of lynx kittens in 2007 and 2008 is now believed to be related to a cyclical decline hare populations. Extensive lynx studies in Canada clearly show the connection between the two species.

State researchers are studying snowshoe hare populations to determine if they can identify population cycles.

Broderdorp said that only a few lynx have died of starvation in the past couple of years.

“That’s pretty good, considering the small population and what we think happened to snowshoe hare populations the last few years,” he said.

Yet it’s still not clear whether the number of new births will offset the number of deaths. If lynx birth rates return to the numbers seen in 2003 (50) and 2004 (39), the answer could be yes. If the reproduction rates stay at the lower levels of the past few years, the cats may have a hard time making a stand in the state.

The Colorado Division of Wildlife’s annual lynx reports and other information is online here.

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