Life Cycle / Mortality

DNR seeks private landowners to help improve deer wintering habitat in Upper Peninsula counties, MI DNR, March 16, 2017Several areas within the eastern U.P. contain deer wintering complexes. Three consecutive severe winters, and subsequent decline in deer numbers, have raised concerns about habitat conditions in these complexes, especially winter shelter.

State releases findings of deer mortality study, Milwaukee Journal Sentinel, Jan 30, 2017So, too, is habitat. In fact, the role of habitat in deer survival is woven through all the results, said DNR researcher Storm. Biologists refer to it as “energetics,” or the amount of energy an animal can obtain from its environment. “So much of deer survival comes down to how much fat they have,” Storm said. “It all starts with the condition of the doe coming through winter.” Higher birth weights are linked to higher survival rates of fawns.

While it is commonly said that adult bucks get so run down during the rut that they are more prone to succumb to winter weather, the study shows something else. In fact, only one of 128 adult bucks monitored through May died of starvation. It was in the northern study area. Here’s what the study showed about last winter: In the north, six of 67 adult and 34 of 102 juvenile males died between Jan. 6 (end of hunting season) and May 31, 2014.

Deer and the Numbers Explosion, Local in Ann Arbor, Feb 24, 2015 The tendency of deer to increase their numbers well beyond the carrying capacity of their environment is termed an “irruption”. This early (1943) paper by Aldo Leopold, one of the fathers of environmental conservation, lays out the story. A reserve owned by the University of Michigan was stocked with 4 does and 2 bucks. Within 6 years, there were 160 deer, and they had exceeded the food supply in a 1200 acre reserve.

Wisconsin deer collisions help further research for Wisconsin DNR, The Outdoor Report, July 2, 2014Regardless of where in the state deer in the study were collected, the evaluations revealed that nearly all adult does were pregnant. “Pregnancy rates among adult does were greater than 90 percent across the state, even in the northern forest,” said Storm. “We wouldn’t expect the severe winter to impact this year’s pregnancy rates, because the deer became pregnant before winter began.”

While adult pregnancy rates did not differ between regions of the state, pregnancy rates of juvenile deer approaching their first birthday and the average number of fawns being carried were found to be quite different from north to south and between major habitat types throughout the state. “The rate of adults carrying twins exceeded 60 percent in both the central and southern farmland zones, while the rate of single fawns for these zones was approximately 9 percent,” said Storm. “In contrast, fewer does in the northern forest zone were pregnant with twins and many were carrying a single fawn.”

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