State wildlife agency testing new method for monitoring wild carnivore populations on a landscape scale
By Bob Berwyn
SUMMIT COUNTY — If you’ve been waiting for the 2011 spring lynx kitten count from the Colorado Division of Parks and Wildlife, don’t hold your breath. Instead if visiting individual dens to collar and count lynx, state biologists are shifting gears, working to determine whether the wild cats can hold their own in Colorado in the long run with an unprecedented habitat occupancy model.
Intensive monitoring during the first 10 years of the state lynx recovery program included annual visits to lynx dens, as well as aerial and satellite monitoring. The research yielded detailed information about lynx behavior and reproduction, including annual reports that specified the number of new kittens as a way of measuring reproductive success. The 2009-2010 annual lynx program report is online here.
But this year, state biologists are switching to a new mode of tracking the rare mountain wild cats. Using a network of motion-activated cameras, snow tracking and genetic sampling, the researchers hope to determine where the cats are living, eating and sleeping, and how well they are filling all the available habitat in the state. An overall assessment of the Colorado lynx recovery program is online here.
The data from those sources will help document the distribution and persistence of lynx across the landscape, said biologist Tanya Shenk, who led the Colorado recovery effort in its first 10 years and now works for the National Park Service as a climate change and landscape ecologist. Shenk said there has been a general move by wildlife and conservation biologists to move away from invasive techniques that put a lot of stress on individual animals. The Colorado Division of Parks and Wildlife lynx program information is online here.
“We think the population is stable at between 200 and 400 lynx,” said biologist Jake Ivan, who leads the lynx team for the state. The cats continue to occupy areas outside the San Juans as their population grows. Lynx dens have been documented as far north as Summit County and beyond.
“We’re getting the sense they’re coming into areas north of I-70,” Ivan said.
The site-occupancy monitoring strategy has been used to track populations of smaller species, but is untested on the broad scale of carnivore populations, according to Eric Odell, the state species conservation coordinator. The researchers said they won’t get as much data on individual cats, but hope that the new approach will provide a better big-picture understanding of the lynx population throughout the state. Similar projects are under way to monitor tigers in India and jaguars in Belize, Odell said.
“It’s a much more efficient and cost-effective way of watching trends in occupied habitat,” he added.
The wildlife agency tested the new monitoring methods in a pilot project in the San Juans during the past two years and is establishing protocols for expanding the program statewide, according to biologist Jake Ivan, who is leading the lynx team. Ivan said lynx are attracted to the cameras by visual cues, including reflective CDs hung from nearby tree branches.
The idea is to try and accurately assess lynx populations broken down into areas that mimic the size of a home range. During the first two years of testing the new method, the researchers still had access to data from radio-collared lynx. That enables the research team to measure how effective the cameras are at capturing the animals in a given area.
The biologists can use those two years worth of detection-probability information to design an effective monitoring program for larger areas, Shenk explained. Using the habitat occupancy modeling will also enable the researchers to get data from more remote areas where there aren’t many records of lynx. In the end, that could help paint a larger and more complete picture of how the wild cats are doing in Colorado.
The medium-size lynx were hunted nearly to extinction during the settlement of the West, with only small populations remaining in three of the 16 states they originally inhabited. The cats were formally listed as threatened by the federal government in 2000 and remain the subject of ongoing legal battles, as conservation groups push the U.S. Fish and Wildlife Service to designate more critical habitat.
The federal government has also been slow to define benchmarks for the overall recovery of the species nationwide, in the form of a national recovery plan.
A year before the listing, the Colorado Division of Wildlife launched a program to restore the carnivores in the state’s mountains and forest., following a tradition of recovering native species. Between 1999 and 2006, biologists released 218 lynx from Canada and Alaska in the San Juans. Researchers started documenting reproduction in 2003, counting 141 kittens through 2010, including several third-generation Colorado offspring in the last couple of years.
Reproduction rates fluctuated, reaching as high as 50 documented kittens in 2005 and dropping as low as zero in 2007 and 2008. Biologists suspect that reproducing cycles change in tandem with populations of snowshoe hares, the primary prey of the cats. Those cycles have been well-documented in Alaska and Canada. The Colorado research showed that lynx were successful in capturing red squirrels when snowshoe hares were scarce, suggesting that lynx can survive the dips in snowshoe hare populations.
Overall, biologists estimate that the cats’ reproductive rate has outpaced mortality — the key factor in determining whether the population will persist and become self-sustaining. In 2010, biologists estimated that about 30 to 40 percent of the female lynx in the state bore litters of kittens.
But climate change, bark beetles, wildfires and development remain as wild cards. All those factors could alter critical lynx habitat in unforeseen ways, according to state biologists.