10 lynx kittens found in 5 dens in Colorado
Summit County correspondent
Aspen, CO Colorado
Colorado’s lynx re-introduction program took a big step forward this spring, as wildlife researchers documented the birth of several third-generation kittens.
Altogether, Colorado Division of Wildlife biologists found 10 kittens spread out among five dens, including a breeding site in Eagle County.
Shenk said three of the dens were in the core release area around the headwaters of the Rio Grande River in the San Juan Mountains. Two of the dens were farther north, one in Gunnison County and one in Eagle County.
“We hope this is an upturn,” said Tanya Shenk, lead researcher for the Colorado Division of Wildlife. “What’s exciting about it is, there were enough lynx out there to get us through our first low,” she added, referring to fluctuating lynx populations that cycle in tandem with snowshoe hares.
The researchers said there is some evidence showing that snowshoe hare populations were at a low point in the 10-year cycle last year or the year before. As a result, female lynx did not produce successful litters during those two winters and springs.
A state-led snowshoe hare study in the Gunnison area is in its third year, and as biologists studied hare densities, some of the results suggesting that hare populations are starting to rebound from a couple of years ago.
Snowshoe hares are the main food source for lynx. They also eat other animals, but expend the same amount of energy catching smaller squirrels as they do to chase down a plump hare. When hares are not abundant, the female cats may abort gestation.
In Canada and Alaska, the intertwined 10- to 11-year cycle of hare and lynx populations is well-documented. It’s not clear if the cycles oscillate with similar amplitude in Colorado.
Shenk cautioned that, gaining a meaningful understanding of hare populations in the state will require 20 years of study, through a couple of cycles.
In two of the dens, both the adult cats were born in Colorado, rather than being lynx that were transplanted from Canada and Alaska. The kittens born this year are third-generation Colorado lynx, marking a significant milestone for the re-introduction program.
Lynx are listed as threatened on the federal Endangered Species List, and Colorado launched its re-introduction program in 1997, bringing a total of 218 lynx to the state. State biologists are tracking about 50 of the cats with functioning collars.
With the tracking data, the researchers have been able to determine that the lynx are mostly using high altitude spruce-fir habitat. The researchers have also been able to identify crucial lynx movement corridors, including the Vail Pass area and another corridor just east of the Eisenhower Tunnel.
“We are very close to achieving all of our goals for the lynx reintroduction,” said Colorado Division of Wildlife lead biologist Rick Kahn. “We have had successful breeding and we have had Colorado-born lynx reproduce. Our next goal is to determine if our level of recruitment is exceeding our mortality rates over a couple of years. We are very encouraged by the results this year and are hopeful that these animals will contribute towards a sustaining population for Colorado.”
As lynx spread from the San Juan release area, they established a secondary core population area in an area centered around Independence Pass, east of Aspen. Some of the lynx have also set up residence in the forested areas between Copper Mountain and Vail.
“We have detected a persistent presence (in Eagle and Summit counties) for two years. Lynx are regularly moving through the Vail Pass area,” said Forest Service biologist Liz Roberts.
That pattern of habitat use has spurred the agency to more intensive study in this region. Last winter, Roberts set up motion-sensor cameras west of Copper Mountain and captured one image of a lynx. Biologists also recorded several more sets of lynx tracks in the same general area.
Lynx were also photographed near a backcountry hut in the Tenmile Range, and on the edge of a trail at Breckenridge Ski Area. A lynx was hit by a car and killed on Highway 9 between Frisco and Breckenridge last year.
Roberts has secured Forest Service funding to take a closer look at the cats in this area. In a collaborative research project with state biologists, she will zoom in on the Vail Pass area. The biologists would like to trap some of the cats and give them new collars with updated GPS transmitters to pinpoint their locations.
With the data, the agencies will do a more detailed habitat analysis. The key questions include how recreation and changing forest health conditions affect lynx.
“What we really want to answer is, how forest health is affecting lynx movement,” Roberts said. “We want to see how much, if at all, they’re using areas hit by pine beetles.” Equally important is to try and determine how recreational use – especially skiing and snowmobiling affect the cats, she added.
Along with the Vail Pass area, Roberts will look at one triangular patch of habitat – formally called a lynx analysis unit – that extends from Hoosier Pass to Peak 5 and east to the vicinity of Boreas Pass. As part of that study, the biologists plan to include a patch of forest on Peak 9 at Breckenridge Ski Area, potentially implementing some terrain management measures that could affect skier access to the backcountry and some hike-to terrain.
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It’s that time of year — hikers and mountain bikers must be aware that seasonal closures are taking effect on multiple trails in the area today for the winter for the benefit of wildlife.