July 11, 2008

The Colorado Division of Wildlife recently completed its annual search for lynx kittens. For the second year in a row no kittens were found.

Researchers believe that the lack of lynx reproduction during the last two years could be related to a decline in the snowshoe hare population. Snowshoe hares are the primary prey of the lynx.

While not seeing reproduction is disappointing, DOW researchers say the adult population is stable and that lynx continue to show encouraging signs that they are adapting well to Colorado. Survival of the lynx reintroduced and born in Colorado is remaining steady, the body condition of lynx captured during winter trapping has been good, and lynx population fluctuation is known to be a natural occurrence in the northern part of their range.

Limited observations by the DOW indicate that the hare population is down from just a few years ago. DOW biologists believe that while adult lynx in Colorado are finding enough food to survive at this time, the females may not be finding enough high-quality food to sustain pregnancy. It is believed that hares provide more of the essential nutrition needed for lynx to reproduce.

In Canada, the population of snowshoe hares fluctuates naturally in multi-year cycles and along with it the population of lynx. It is not known for sure if snowshoe hare populations cycle in Colorado, but recent trends suggest some degree of fluctuation.

Observations of the lynx population by DOW researchers show the cats are establishing good social structures and exhibiting breeding behavior; males are establishing territories and lynx are behaving as they should in the wild.

Researchers also note that a large percentage of the lynx radio collars have stopped operating and the vast majority of kittens born in Colorado have not been fitted with the transmitters. Consequently, DOW estimates of lynx survival and the number of kittens produced is very conservative. The dens located by field staff are representative of the minimum number of litters and kittens in a reproduction season.

The reintroduction of the animals in Colorado started in 1999. Since then 218 animals have been released and the DOW has recorded birth of a total of 116 kittens. With that number of animals living primarily in wilderness areas researchers cannot track the activities of every cat. "When we started the program we could track individual animals," explained Rick Kahn, lead biologist for the reintroduction project. "But now lynx have established themselves over a wide area and looking at specific numbers does not provide an accurate picture of what is happening with the population. We are most encouraged by the fact that overall long-term survival of adults remains at a high level."

During the winter the DOW traps adult lynx to replace radio collars and to check the general health of the animals. The cats trapped during the last two winters were in good shape and the mortality rate was low, explained Tanya Shenk, field research leader for the DOW's reintroduction program.

"The cats are finding enough to eat. We're very pleased with their body condition and the survival rate," Shenk said. "We are now dealing with a wild population. It's very challenging to track and trap animals. We have documented reproduction by reintroduced animals and we've had reproduction by animals born in Colorado. We know they can function fully in our environment. Fluctuation of hares and lynx is a classic biological predator-prey interaction. The natural system will usually readjust itself," Shenk said.

The DOW is funding a small-scale study to examine snowshoe hare population in the Taylor Park area. While that study is in a limited area, judging by the lack of lynx reproduction during the last two years hare population may possibly be down statewide.

DOW researchers are still regularly monitoring 50 of the original 218 lynx released in Colorado that are equipped with radio transmitter collars. They have documented 109 known mortalities. The status of 59 of the released lynx is unknown because the radio collars are not functioning. In addition, kittens born in earlier years in Colorado are likely surviving and reproducing.

Kahn explained that the DOW will continue intensive monitoring of the lynx, and a snowshoe hare research project will continue next winter. Release of additional cats is not planned.

The DOW started planning the lynx reintroduction program in 1997. Cats were released in Colorado's southern mountains in 1999, 2000, 2003, 2004, 2005 and 2006. The cats were brought to Colorado from Alaska and Canada. 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.

The lynx reintroduction program is funded by the DOW, Great Outdoors Colorado which receives its funding through the Colorado State Lottery, and private donors.