Biologists not sure why Colorado's rare lynx didn't reproduce this year
Vail, CO Colorado
August 1, 2007
SUMMIT COUNTY — A dramatic decline in lynx reproduction the last two years won't change the way federal agencies manage the rare wild cats in Colorado.
"From our perspective, nothing will change," said U.S. Fish and Wildlife Service 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 Endangered Species Act.
The Fish and Wildlife Service 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 try to make sure no harm will come to the lynx.
The Colorado Division of Wildlife reported last week that no newborn kittens were found this year. Biologists with the recovery effort said a shortage of snowshoe hares, a main food source for lynx, 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.
Rockies a good home?
Broderdorp said there is no reason to panic.
"This is not an unnatural event. It's not unexpected," Broderdorp said.
Lynx populations in Canada and Alaska are known to fluctuate dramatically in tandem with the number of snowshoe hares, he said.
But even when hare numbers drop to their lowest levels in those areas, there is generally still some limited lynx reproduction, he added.
"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. "We'll continue our intensive monitoring efforts and data analysis and wait to see what happens next year."
Kahn said it's possible there were some births among lynx that aren't 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, we're seeing a lot fewer hares," Kahn said.
Tracking hares would require extensive 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.
The Division of Wildlife 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.
The DOW has released 218 lynx in Colorado's southern mountains between 1999 and 2006.
Lynx generally live for about 10 years and reproduce between the ages of three and eight, although older cats have been known to breed.
The Colorado Division of Wildlife is not sure of the exact ages of the cats transplanted to Colorado from Alaska and Canada.
It's hard for the biologists to imagine what else might be causing the drop in reproduction. Kahn said it's 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 breeding.
"It could even be more sinister than that," Kahn added, suggesting that biologists may have to face the reality that the southern Rockies simply don't provide good lynx habitat.
Gary Patton, a U.S. Forest Service biologist who was involved in the early stages of the state's recover effort, suggested that researchers should be open to other possibilities than hares for the drop in lynx reproduction.
"I don't know if there's a way to determine in the short term whether hare population cycles are the cause," Patton said. "It's 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. Changes in the vegetation patterns due to drought or even global warming could also cause drops, he added.
Bob Berwyn can be reached at (970) 331-5996, or at bberwyn@sum
A total of 116 lynx kittens are known to have been born in Colorado:
16 kittens in 2003;
39 kittens in 2004;
50 kittens in 2005;
11 kittens in 2006
0 kittens in 2007