Oct. 1, 1999 Moose populations are relatively low in the Yellowstone area and some blame the wolves and grizzly bears that are returning after a 60-year absence. But new research shows that fewer moose are getting pregnant, suggesting that the real reason is there simply isn't enough food for more moose.
This study is presented in the October issue of Conservation Biology by Joel Berger of the University of Nevada in Reno, Ward Testa of the Alaska Department of Fish and Game in Anchorage, Tom Roffe of the U.S. Geological Survey in Bozeman, Montana, and Steven Monfort of the National Zoological Park in Front Royal, Virginia.
To determine moose pregnancy rates, Berger and his colleagues analyzed fecal progesterone levels. They found that in protected areas of the greater Yellowstone ecosystem, moose pregnancy rates fell from 90% in 1966 to 75% today, making them among the lowest in North America. This suggests that the drop in young moose is not due to wolves and grizzly bears. Rather, the researchers suspect that the number of moose is limited by the abundance of willows, their major winter food.
"We are pushing the envelope here and suggesting that knowing pregnancy rates can tell us whether populations are at or above the food ceiling of their ecosystem," says Berger.
The researchers' fecal pregnancy test will help people monitor the effects of large carnivores as they are restored to reserves in North America, Europe and Africa. The fact that the test is non-invasive makes it particularly useful in national parks, where handling animals is generally discouraged, and in remote areas, where reaching the animals is difficult.
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