Deer quickly rebound from winter losses
By Jim Lee
Gannett Wisconsin Newspapers
MINNEAPOLIS –Hunters concerned about Wisconsin’s deer population may find some solace in a report from a neighboring state.
The deer herd in portions of northern Minnesota sustained 20 percent losses during the severe winter of 2008-2009 even as wolf and bear predation increased, but that’s no cause for long-term concern, biologists in the Gopher State say.
“A groundbreaking study of does’ reproductive capacity shows that our north woods could soon be teeming with whitetails again,” reports the Minnesota Department of Natural Resources.
Research biologist Glenn DelGiudice recently conducted a 15-year study of deer survival and reproduction in the Chippewa National Forest in north-central Minnesota. The project, which began in 1991, monitored 477 radio-collared female deer in an area of extensive wolf activity.
“As the longest-running designed field experiment ever conducted on deer, it has helped to rewrite the book on what wildlife biologists know about deer survival and reproduction,” the Minnesota DNR stated in a recent article by Gustave Axelson.
DelGiudice found that while harsh winters can be fatal to some deer, lower deer numbers improve habitat quality and subsequently doe fertility, thus hastening the herd’s rebound during periods of relatively mild winters.
He also found that wolf predation, which tended to focus on older and weaker deer, had little impact on the resurgence.
“It seems like these findings will be useful in explaining some of the wolf-deer interactions in Wisconsin as well,” said Keith Warnke, leading deer biologist for the Wisconsin Department of Natural Resources.
“The two states are very close in proximity and in many habitat characteristics and in many deer biology characteristics.’
Adrian Wydeven, wolf expert for the Wisconsin DNR, said wolf behavior in this state appears comparable to that found in Minnesota.
“We have not really done a systematic assessment of wolf-killed deer in Wisconsin, but based on my anecdotal examination of wolf-killed deer over the years I would agree that we probably have similar patterns … with a high percentage of fawns and older deer in the wolf kill.
“Middle-aged does (2-7 years old), unless sick or injured, are almost immune to predation by wolves.
“Middle-aged bucks (2-5 years old) are probably mostly immune to wolf predation, but right after the rut when their energy reserves are exhausted, they are probably more susceptible for a while.”
Warnke said annual buck mortality is 50-70 percent in Wisconsin “and we believe that upwards of 80 percent of that mortality is due to legal hunting.” Other factors, including age, accidents, automobile collisions and predation account for much of the remaining toll.
DelGiudice reported occasional instances –when Minnesota’s winter conditions allowed — that wolf packs went on excess killing sprees in some deer yarding areas.
“During certain crusty snow conditions, most deer encountered are catchable and that is when we would expect surplus killing,” Wydeven said. “We have not verified surplus killing in Wisconsin since about 1996-97.”
Conditions for deer survival during the winter of 1996-97 were the worst ever recorded by the Wisconsin DNR, yet “by 2000 the statewide (deer) harvest was over 600,000 animals,” Warnke said.
The Wisconsin countryside is divided into deer management units. The DNR attempts to maintain deer numbers in each unit at levels acceptable to the public and the land’s carrying capacity.
The Minnesota study attributed a restriction on antlerless harvest permits along with mild winters as key factors in a herd’s rebound.
“That is part of our strategy,” Warnke said, pointing out that no antlerless permits were issued for Units 39, 40 and 50 in far northeastern Wisconsin this fall. “These are areas chronically below goal where habitat is not as suitable for deer as it once was.”
Minnesota’s research does not blame wolves for fluctuations in the deer population.
“We studied an area saturated by wolves, with high hunter access and some historically severe winters and yet white-tailed deer still thrived,” the article quotes DelGiudice.