Colorado Study of Mule Deer Aging Shows Positive Results

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Early results of a mule deer aging study being conducted by the Colorado Division of Wildlife are helping provide insight into the trade-offs between hunt quality and hunting opportunity in southwest Colorado.

The DOW asked hunters to submit teeth from bucks harvested in Game Management Units 54, 61, 62, 80 and 81 during the 2007 big game season. Biologists determine the exact age of a mule deer by counting the annual growth rings present within an animal's incisors. The DOW sent mailings to 2,065 hunters in 2007 explaining the project and asking them to send teeth from harvested bucks. Last year, 375 teeth were returned.

Biologists plan to continue this research for the next two hunting seasons.

"The return rate in 2007 gave us an excellent sample to start with," said Brandon Diamond, a terrestrial biologist for the Colorado Division of Wildlife in Gunnison. "There are three management units involved in this project that have contrasting buck-to-doe ratio objectives. GMU 54 has the highest ratio followed by GMUs 61 and 62, and finally GMUs 80 and 81."

The results show that the age structure of bucks harvested varies between the GMUs, as biologists anticipated. "The purpose of this study is to determine that in units where we manage for high buck-to-doe ratios that hunters actually are taking more older-age-class bucks," Diamond said.

Biologists are interested in evaluating whether there is an optimum buck-to-doe ratio to which they can manage that maximizes both hunt quality and opportunity. "Hunters across the west love to see big mule deer bucks. But they also want the chance to hunt them on a regular basis. We are trying to find the best middle ground," Diamond said.

GMU 54, just north of Gunnison, has in recent years become renowned for its mule deer. It is managed for a high buck-to-doe ratio of 40-45 bucks per 100 does; the 2007 post-hunt population estimate was approximately 7,500. Despite the tougher hunting conditions during the 2007 seasons due to unseasonably warm and dry weather, the first-year results of this project are really interesting, Diamond explained.

"In unit 54, the majority of hunters submitted teeth from bucks that were between 3-6 years old. It appears we have a lot of bucks that are 4 years or older, which should be the case due to our management prescriptions. Because of current management, hunters can be selective and they are seeing greater numbers of older bucks," Diamond said.

In GMU 54, bucks up to 9 years old were harvested.

"Maintaining so many older-aged bucks, however, doesn't come without sacrifice," Diamond explains. "In many southwest Colorado deer units, deer hunters will have to sit on the sidelines for several years between hunts.

Many hunters would like to hunt deer every year and have the opportunity to harvest a buck four years old or older. The reality is that you can't have it both ways."

GMUs 61 and 62 are located on the Uncompahgre Plateau, west of Montrose. This area provides excellent deer habitat. The estimated population is 32,000, and the sex ratio is estimated at 35 bucks per 100 does. Teeth submitted from hunters in 2007 were predominately between 1 and 4 years old; however, some bucks as old as 9 years were harvested.

In GMUs 80 and 81 in the San Luis Valley the deer population is estimated at 5,900 with a buck-to-doe ratio of approximately 24 to 100. Most of the bucks harvested in the area were from 1 to 3 years old, with a few bucks as old as 7 years.

The DOW is urging hunters in these units to send in teeth from the harvested animals, particularly in GMUs 62 and 61 which had the lowest overall response in 2007. Overall, Diamond hopes to collect about 1,000 teeth as the study continues for the next two years. This project will also help managers evaluate the changes in mule deer populations following the severe winter of 2007-2008.

"We have made it as easy as possible to participate in this project, so hopefully hunters will take a few minutes to send in their tooth," Diamond said. "The bigger the sample size, the more we'll learn about how our deer management prescriptions are working."

The DOW hopes to continue this project through the fall of 2009 so that three years of data are available for comparison. For the 2008 season, hunters can expect age results by May or June of 2009. Results will be posted on the Division of Wildlife's website as soon as possible so that hunters may check the age of their individual deer on-line.

Hunters who have drawn tags in these units may receive an envelope and a letter of explanation before the start of the 2008 season. In some units, a sub-sample of hunters was selected to participate in the project, so not everyone will receive a mailing. Only those who harvest bucks are asked to send in teeth.

Thanks to a generous donation, hunters who send in teeth in 2008 will have a chance to win a rifle donated by the Mule Deer Foundation.

If you hunted in any of the units last year and you sent in teeth, you can check the age of your animal on the DOW web site. Go to: http://wildlife.state.co.us/Hunting/BigGame.

Hunters with questions can call Diamond at (970) 641-7071.