Published March 04, 2012, 12:00 AM

Wisconsin deer study: First-year data holds some surprises

Preliminary results from a study of white-tailed deer in Wisconsin indicate that fewer adult bucks are surviving from one winter to the next than Department of Natural Resources officials had previously estimated.

By: Sam Cook, Duluth News Tribune

Preliminary results from a study of white-tailed deer in Wisconsin indicate that fewer adult bucks are surviving from one winter to the next than Department of Natural Resources officials had previously estimated.

Buck survival is one measure the DNR uses in its SAK (Sex-Age-Kill) model used to manage the state’s deer herd. Study authors from the University of Wisconsin and the DNR caution that these results represent just one year’s data from what will be a long-term study of deer in the state.

In the study, 339 adult deer and 104 fawns were captured and radio-collared in 2011. The deer were captured in two study areas, one in northern Wisconsin (Sawyer, Price and Rusk counties) and another in a farmland area in eastern Wisconsin.

In the northern study area, 78 bucks and 40 antlerless deer were radio-collared. Fifty-nine radio-collared deer died through Dec. 31, according to the report. Hunter harvest and predation were primary causes of death. Predation was responsible for 14 deaths. Wolves and bobcats were the primary predators of yearling male deer. Nine deer died as a result of the capture process. Five adult bucks were poached.

“I would never have predicted we’d have that level of poaching, especially on radio-collared deer,” said Greg Kessler, DNR area wildlife manager at Brule.

Nineteen of 38 adult bucks (50 percent) in the northern study area survived from one winter to the next, according to the study, which is “substantially lower” than the DNR’s model-derived estimates of 70 percent. Despite the fact that adult buck survival is lower than the estimate used by the DNR in its SAK model, study authors said the 50 percent survival is “comparable to the survival rate (60 percent) reported across the Midwest during the past 20 years.

In the northern study area, 22 of 30 (73 percent) radio-collared fawns died through Dec. 15, 2011. Most of those mortalities occurred from late May through late June and were attributed to predation. Predation was caused by black bears (5 fawn deaths), bobcats (2), a coyote (1), an unknown canid (2) and unknown predators (4), according to the report.

The 27 percent fawn survival in the northern study area “is comparable to the range of survival rates (28 percent to 76 percent) documented elsewhere across the United States,” according to the report. However, in explaining why this long-term study was undertaken, study authors said there is concern among wildlife managers and others that with increasing populations of large predators (black bears, wolves, bobcats and coyotes), there is growing concern that predation on fawns may be limiting recruitment in white-tailed deer.

“The fawn mortality seems high,” Kessler said, “but it’s within the range of what we’ve predicted in the past.”

Crews, including hundreds of citizens, have been trying to capture and radio-collar more deer for the second year of the study, Kessler said. In subsequent years, radio-collaring will be replaced by using ear tags to monitor deer survival, he said.

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