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UP Deer Abundance Factors
In Michigan, there are numerous factors that may act singularly or in combination to influence deer abundance and they can vary over space and time. Some of these factors have a greater impact on deer populations and thus are more important than others. In addition, some of these limiting factors can be managed by state wildlife agencies, while others cannot. For an in-depth look at the important limiting factors affecting deer abundance in the Upper Peninsula, along with the complex interactions among predators and prey please see the complete report linked at the bottom of this page. Below is a brief summary of two of the major take home messages.
The graph below depicts the relationship between buck harvest and winter conditions in the Upper Peninsula. Winter conditions are shown by the blue-shaded area and winters above the horizontal blue line are considered severe (greater than 90 days of 12 inches or more of snow on the ground). When the duration of snow cover exceeds the horizontal, dotted blue line, winter is likely to impact deer populations to some degree. Buck harvest (shown with the dark blue bars) was at an all-time high from the late 1980's to the mid-1990's and winters were noticeably milder during this time period. The consecutive severe winters beginning 1996 and 1997 have resulted in periodic declines in buck harvest since then. In fact, in the last 11 years, there have been six severe winters that have impacted buck harvest, further restricting the growth of the UP's deer herd.
Wolves, more so than other predators, are often blamed for a lack of deer. The graph below shows relatively stable minimum wolf population estimates (black squares) for the last 12 years, roughly falling between 600-700 animals. During this same time period, buck harvest (blue line) in the Upper Peninsula has increased and decreased numerous times, nearly doubling from 2015 to 2017 (despite a stable wolf population). This data shows that changes in the Upper Peninsula deer population are not primarily driven by wolf population levels or wolf predation. Meaning, when deer numbers decline, it is not because wolf numbers have increased and when deer numbers increase, it is not because wolf numbers have declined. Deer have co-evolved with predators (including wolves) and as such, have developed predator avoidance behaviors (selecting habitat outside of wolf core areas) and physical characteristics which increase survival.
The data and graphs found in the "Factors Limiting Deer Abundance in the Upper Peninsula" complete report show that predation from wolves has a relatively small impact on the deer population. This is because wolves are not the main predator on fawns, and fawn survival is what drives the deer population changes in most years and while wolves prey on adult deer, adult deer survival is quite high. Wolf predation, winter weather, predation by other species, habitat quality, changes to deer harvest regulations, declining hunter numbers, and changes in timber harvest all play a combined role in changes to the deer population in the Upper Peninsula. Predation from wolves is simply one portion of what impacts our deer herd in the UP, they are not solely responsible for yearly population variations.