News good so far for mule deer
The calendar tells us winter starts in late December and ends in late March.
For mule deer and other ungulates, winter starts with the first snow and doesn’t end until the spring “green-up,” which may come in late May.
If the green-up arrives too late, thousands of deer might die.
That’s why wildlife biologists carefully monitor the body condition of the state’s big-game herd, trying to anticipate potential problems before they appear.
So far, the news is good, with relatively light snow and a bit of a break from the deep cold of December.
“Given the snow depths and the relief from the really cold weather we had this weekend, at this spot we’re in pretty good shape,” said Lyle Sidener, area wildlife manager for Colorado Parks and Wildlife in Hot Sulphur Springs. “The cold weather was short and not the two to four weeks of subzero temperatures we sometimes get.”
Mule deer are selective browsers, in the summer eating a variety of foods, including sagebrush, serviceberry, aspen, willow, mountain mahogany, grasses and forbs.
When grasses and forbs die in winter, the deer eat more shrubs, which stick up above the snow and provide vital protein and carbohydrates.
Deer, though, have a digestive system that makes up about 10 percent of their body weight. A bison’s digestive system may be 24 percent of the body weight.
A smaller digestive system limits how much a deer can eat at one time and requires them to be more selective about the quality of forage they consume.
In summer, this poses no problems. In winter, with everything in short supply, it means more time spent seeking out the best available forage.
Deer depend on sagebrush for their main winter forage, particularly the new growth on the tips of branches. When deep snows cover the sagebrush, or long-term drought such as the West has been facing prevent this new growth, a deer’s winter can be bleak.
“They’re draining their reserves” throughout the winter, Sidener said. “We can get to the point where there is no recovery if we get a bad winter storm in late spring.”
A late spring is particularly impactful on fawns, state terrestrial biologist Brad Petch said.
“It’s too early to tell yet on the fawns,” Petch said. “Even as late as late spring you can see some mortality, but so far things look pretty good, at least in the northwest region.”
Having a wet summer helped survival chances, biologist say.
“Two years ago we were so dry the animals had trouble finding enough food,” said J Wenum, area wildlife manager for the Gunnison Basin. “This year that went out the door. There was water and food everywhere.”
That means deer went into winter with more body fat, the only reserve they have when food is scarce.
“Last year was a really good year with food and water at all elevations,” Wenum said after a recent aerial survey of part of his area. “All the animals we’ve seen all look to be in very good shape for this time.”