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Colorado Biologists Studying Pervasive Deer Disease

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Colorado Parks and Wildlife biologists recently began monitoring mule deer bucks in the North Fork Valley in an effort to better understand a disease that causes antler deformities and the possible long-term effects on herd health.

During the past 10 years, hunters and residents of the Hotchkiss and Crawford areas have reported a high number of so-called “cactus bucks.” In these male animals the antlers grow in odd shapes, never develop fully and do not lose their velvet. Biologists think that the antler deformities are indicators of hemorrhagic disease which is caused by viruses transmitted by bites from small insects called midges. But they don’t understand why the disease is particularly prevalent in this area of Colorado. Hemorrhagic disease can also affect white-tailed deer and pronghorns.

In early January, biologists captured and put radio transmitter collars on eight infected animals, said Brandon Diamond, Gunnison-area terrestrial biologist for Parks and Wildlife. Bloods samples were taken and each deer’s physical condition was assessed.

“With the radio collars we’ll be able to follow their movements, determine if they lose their antlers, and whether they re-grow normal antlers,” Diamond said.  ”At the same time we’ll also be able to evaluate their annual survival rates.”

The viruses transmitted by the insect bite interrupt hormone production and cause atrophy in the testicles. Infected deer may only suffer a transient fever; however, some animals become lethargic, develop ulcers on their mouths and tongues, show respiratory distress, lose their appetite and suffer internal bleeding. Midges are most prevalent in wet areas, and biologists believe that deer become infected when they are concentrated around water holes.

Diamond explained that licensed hunters are allowed to harvest “cactus bucks” during the annual deer seasons. The virus does not infect humans and there is no risk from handling or eating venison from these deer.

While the disease can be fatal, biologists are trying to learn whether infected animals return to normal health and breeding status.

“Right now, the focus is on bucks because their antlers allow us to identify that they’ve been infected and to observe changes over time,” Diamond said.

The radio collars can transmit for up to five years, providing biologists the opportunity to make long-term observations. The collars also are expandable so they accommodate the bucks’ increased neck size during the breeding season.

The deer were captured on private land.

“We really appreciate the cooperation from the landowners and the public support for this project,” Diamond said. “We hope to continue this project for several years and we may continue to capture animals in the future to boost our sample size.”

Read about mule deer in Colorado at:  http://wildlife.state.co.us/WildlifeSpecies/Profiles/Mammals/Pages/Deer.aspx.

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