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Drop in lynx births spurs questions

BOB BERWYNSummit County CorrespondentGlenwood Springs, CO Colorado

SUMMIT COUNTY A dramatic decline in lynx reproduction the last two years wont change the way federal agencies manage Colorado habitat for the rare wild cats.From our perspective, nothing will change, said U.S. Fish and Wildlife Service (USFWS) biologist Kurt Broderdorp, who works with the U.S. Forest Service to ensure that activities like logging, recreation and ski area expansions are consistent with the recovery guidelines of the Endangered Species Act.The USFWS is responsible for animals listed as threatened or endangered. Most of the suitable lynx habitat in Colorado is on national forest land, so before the Forest Service approves a project, biologists from the two agencies make sure there are no significant adverse impacts to lynx.The Colorado Division of Wildlife (CDOW) reported last week that no newborn kittens were found this year. Biologists with the recovery effort said a shortage of snowshoe hares may be the main reason for the lack of new births. Snowshoe hare numbers may be at a low point in a natural population cycle, the researchers speculated.The state wildlife agency keeps close tabs on lynx via radio signals sent from special collars on the cats. In late winter, they track males and females in close proximity to each other. Then, when the female stays in one place, they have a good idea that the lynx may be setting up a den for breeding. Biologists and trackers subsequently visit the den sites to count kittens.For several years , hopes were high that the cats were well on the way to recovery after numerous lynx births were reported between 2003 and 2006. But the lack of newborn lynx kittens this year is troubling and has caused some concern among biologists involved with the recovery effort. But Broderdorp said there is no reason to panic.

This is not an unnatural event. Its not unexpected, Broderdorp said, referring to the fact that lynx populations in Canada and Alaska are known to fluctuate dramatically in tandem with the number of snowshoe hares, the main prey species. Broderdorp did say that, even when hare numbers drop to their lowest levels in those areas, there is generally still some limited lynx reproduction.The cycles (in Colorado) may be more localized and lower amplitude, Broderdorp said, adding that there are no definitive studies from Colorado as yet to show a decline in hare populations.With the number of lynx currently in Colorado, we believe they could go two or three years without reproduction and still have enough survivors to rebuild the population, said Rick Kahn, lead biologist for the reintroduction effort. Well continue our intensive monitoring efforts and data analysis and wait to see what happens next year.Kahn said its possible there were some births among lynx that arent equipped with collars. But the fact that there were no births among the cats that the agency can track leads researchers to believe that something is up.Anecdotally, were seeing a lot fewer hares, Kahn said, acknowledging that CDOW doesnt yet have hard scientific data to show whether Colorado hare numbers are at a low point in some kind of cycle.That would require extensive and standardized monitoring over a widespread area. And pinpointing the length and intensity of a hare population cycle means studying the numbers through one or two entire cycles, said University of Wyoming biologist Steve Buskirk, who was part of an early science advisory team on the lynx recovery effort.CDOW has started an intensive hare monitoring effort in south-central Colorado, Kahn said, but the agency is nowhere near having definitive data on hare populations.But its hard for the biologists to imagine what else might be causing the drop in reproduction. Kahn said its possible the lynx themselves might be be eating hares at an unsustainable rate. There has also been speculation that repeated introductions of new lynx transplanted from Canada and Alaska could have an impact on the social breeding structure of the cats.It could even be more sinister than that, Kahn added, suggesting that biologists may have to face the reality that the Southern Rockies simply dont provide good lynx habitat.

Its not completely clear if hare populations in the Southern Rockies follow a similar cycle. There is some speculation that the cycle may be shorter, and that the swing in numbers may not be as great, said Gary Patton, a U.S. Forest Service biologist who was involved in the early stages of the states recover effort.Patton suggested that researchers should be open to other possibilities for the drop in lynx reproduction.I dont know if theres a way to determine in the short term whether hare population cycles are the cause, Patton said. Its still debatable whether snowshoe hare numbers cycle substantially in the Southern Rockies.Patton said an extended drought in the San Juans, with diminished snow cover, could be a factor, as could be changes in the vegetation patterns due to drought or even global warming.Bob Berwyn can be reached at (970) 331-5996, or at bberwyn@summitdaily.com.


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