OUT: DOW eyeing number of bucks

Commission likely to give intense study to doe portion of state’s deer population

THIS FAWN WEARS a radio collar as part of a deer survival study on the Uncompahgre Plateau. While some deer herds are continuing to increase to number, others aren’t responding as well as wildlife managers had expected. Several theories are being tested, including whether higher buck numbers along with an older doe population affect overall reproduction rates.

With the start of the 2008 general big-game hunting season less than two weeks away, the Colorado Wildlife Commission could be accused of being a bit premature by focusing on the 2010-2014 seasons.

But the two intervening years will go quickly, especially considering the amount of work and immense number of decisions to be made before the commission can put its final stamp on the framework for upcoming hunting seasons.

Managing elk and deer herds always have been ticklish matters which hopefully end in a way many hunters seem to take for granted: that somehow they’ll obtain a license to chase an elk or deer.

Assuring those herds are healthy and deciding how much harvest a herd might support are key to that end result of having licenses to issue.

In the past decade, Colorado deer hunters have seen their sport go through serious restructuring, the most impact coming from a wildlife commission decision in 1999 to totally limit all deer licenses.

With an eye on the state’s dwindling deer herds, it was thought putting hunting caps on bucks would give the herds a needed boost.

It did, but not in the way expected.

“When we went to limited deer licenses, we saw an increase in deer numbers, just as we expected,” said

DOW big-game coordinator Bruce Watkins. “But the increase was mainly on the buck side. We’re not exactly sure why buck numbers respond to decreased hunting pressure while doe numbers can remain fairly flat with little or no hunting pressure.”

Watkins said part of the answer might be simple math. Prior to going to limited buck tags, a lot of bucks were killed each year. Now, there are more bucks left after each hunting season, which results in an overall increase in deer numbers.

Math on the doe side is less clear, he said.

While doe licenses have increased since 1999, the doe harvest remains only a fraction of the buck harvest, even in units where doe harvest is encouraged to control herd numbers.

Biologists expect a pulse of yearling does each year, just as they see a similar pulse of yearling bucks. So why haven’t doe numbers increased similar to buck numbers?

“We’ve usually made the assumption the buck and doe survival outside of hunting were pretty similar, but that might not always be the case,” Watkins said. “The literature is mixed on differences in buck vs. doe survival in mule deer.”

Because the doe harvest is much lighter than the buck harvest, the doe age structure is more top-heavy, meaning there usually are a lot of older does in the population.

This inverted age structure in does could contribute to higher natural mortality in does compared to bucks.

Watkins said contrary to what most people think, doe mortality in some parts of the state can be higher in the summer and fall than in the winter.

“Some of that could be due to additional stress from fawning and lactation,” he said.

Mortality on the doe side is one reason deer herds aren’t recovering as fast as expected. The DOW has a statewide deer population objective of 586,000 animals, but last year the post-hunt estimate was 536,000, a sizeable drop from the 550,000 in 2004.

“The 2007 post-hunt estimate was before last winter, so it indicates deer populations statewide already were flat or somewhat declining,” Watkins said. “In some areas where we are close to objectives, we have increased doe harvest to control population numbers.”

In some units that are below objective, some doe harvest is occurring to keep the population’s age structure from getting too top-heavy, Watkins said.

Since 2002, deer herds statewide have exceeded the objective of having 29 bucks per 100 does.

He said the population rise resulting from an increase in buck numbers because of limited licenses is likely as high as it will get.

“We put a lot more mouths out there to feed by increasing the buck population,” Watkins said. “Doe numbers stayed about the same, and now it appears that fawn recruitment may decrease when buck numbers are high.

“This could be one reason why (some of) our deer populations are going down.”
Watkins said the division is developing a pilot study to monitor buck survival.


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