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The Wisconsin Department of Natural Resources and the University of Wisconsin – Madison has been conducting a large-scale study of deer mortality. This study is the largest of its kind ever conducted in the state of Wisconsin.
Since the winter of 2011, radio-collars have been placed on over 700 deer. Radio-collars allow researchers to determine the proportion of deer that survive each year, and in most cases, the cause of death to individual deer. Wisconsin focused on collaring bucks in the winter and newborn fawns in the spring.
The research includes two large study areas. The Northwoods study area has large tracts of forest while the farmland study area has large tracts of cropland. The Northwoods study area has fewer hunters and roads than the farmland study area, yet more predators. The differences between these two areas provide the researchers with a better understanding of how deer survival varies across Wisconsin.
The preliminary data is starting to reveal some interesting patterns on fawn survival. In the first three months of life, survival of newborn fawns in the Northwoods varied substantially year-to-year, with survival ranging from 22 percent to 52 percent. Predation is the most common cause of death for fawns in the Northwoods. Predation of fawns by bears, bobcats, and coyotes have all been confirmed.
In the farmland study site, fawn survival has ranged from 58 percent to 62 percent. Surprisingly, the most common cause of death for fawns in the farmland was starvation, not predation. This may indicate that some does are not receiving adequate nutrition to care for their fawns.
In addition to fawns, the study investigates adult buck survival. For adult bucks, hunter harvest is the number one cause of death; it is about 3 times the rate of all other causes combined. Road kill was the second leading cause of death in the farmland study area; while in the Northwoods, the second leading cause of mortality was winter kill.
Winter kill includes several causes of mortality that occurs in late winter/early spring. Winter kill is more common during severe or prolonged winters because deer exhaust their energy reserves (body fat) and become vulnerable to starvation, exposure, and predators. Deer experiencing a severe winter in their first year of life are particularly vulnerable. While some deer being monitored were clearly killed by predators (mostly coyotes and wolves), some clearly starved to death. Other deer were obviously consumed by predators, but it was unclear whether they were preyed upon or scavenged.
The project is in the midst of its fourth and final year of capturing adult deer. When the study is complete Wisconsin will have a much better understanding of the causes of deer mortality.
Special Note From Wisconsin Department of Natural Resources: Wisconsin is greatly appreciative of SCI Foundation for their crucial support of this project! In particular, SCI Foundation graciously donated $10,000 worth of radio collars, $15,000 used to purchase 2 pickup trucks, and an additional $25,000 used to fuel these vehicles and pay technicians. Needless to say, these donations have been critical to our projects’ success!
Project Update Courtesy of the Wisconsin Department of Natural Resources
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