Deer Biology and History

A deer population doubles in size approximately every two years if it is not reduced by predators or hunting or an epidemic. Female deer have one to three fawns every year and are first fertile when they are only six months old. See Reproductive characteristics of female white-tailed deer

As a prey animal, deer are prolific. The image to the right shows this graphically. The Bridge Michigan magazine article, “Why Ecologists Support Ann Arbor’s Deer Cull,” cites a U-M landmark study. “We can look to the University of Michigan’s E.S. George Reserve. In 1928, four does and two bucks were released into the 1300-acre research tract. The population increased from six to more than 160 animals in six years.”

In much of North America, humans have eliminated the wolves, cougars, and bears that had previously controlled deer populations.  Settlers also killed deer for commercial sale and almost exploited them to extinction by the beginning of the 20th century, including in Michigan. See: American Heritage, ”The Return of the White-tailed Deer.”

States prohibited commercial sale of deer products and set limitations on sport hunting, so deer populations grew back from fewer than one million in the US at the turn of the 20th century to 30+ million now. The deer population throughout the US is managed via hunting. In Michigan, approximately 365,000 deer are harvested by hunters every year, from a population of about 1.75 million deer. More info is at Michigan DNR – Deer Management History in Michigan  Pennsylvania also offers us a fascinating and complicated history of deer management, “History of the Whitetail.”    

Deer are browsers, not grazers. They thrive in an edge habitat, the transition area between woodlands and open lands, where there is an abundance of browse plants. Suburbs and housing subdivisions did not “drive them out” but provide excellent habitat, better than the deep woods or open fields. From the Smithsonian Magazine, Oh Deer! “Edges abound in plants deer can munch. Originally, the eastern United States was one deep, dark forest. Now it’s deer nirvana. It’s one big edge.”

Deer multiply rapidly in suburban habitats and park woodlands. There has been a marked increase in the local deer population in Ann Arbor just since the turn of the 21st century, when local residents began to notice their presence.  This is due to natural reproduction by the local animals, not due to increased infiltration from other areas or from displacement by real estate development.   Does have a strong allegiance to the home range that they were taught by their mother. They don’t distribute evenly (i.e. they aren’t gas molecules), they stay in the same area their whole life – see the Journal of Wildlife Management, Localized Management of White-tailed deer in the Central Adirondack Mountains, New York.

Deer populations will continue to grow until they eat all the food available. There is no biological mechanism that limits herd growth other than predators. Aldo Leopold documented deer overpopulation in larger landscapes and the resulting starvation, overbrowsing damage, and population collapse. It also happens locally. In 2018, WXYZ News in Detroit reported on deer on a Detroit area property exceeding biological carrying capacity and the resulting starvation. Deer Continue to Die on Fenced Private Property.

False Claims that Lethal Deer Management Cannot Succeed

The Humane Society of the United States and others have advanced the argument that hunts and culls cannot actually reduce deer density. They propose two mechanisms that doom lethal herd control to failure: the “vacuum effect” and  “reproductive rebound”.

The vacuum effect – the hypothesis that deer are “sucked in” from neighboring areas when deer are removed, i.e. that deer disperse into available territory. This hypothesis has been disproved by Dr. Porter’s research in upstate NY. Deer were removed from an area surrounded on all sides by other deer herds. No deer moved into that area during a two year period. The research was extended and no deer moved into that area for 5 years. The reason behind that is that fawns learn a home range from their mother and have an allegiance to that maternal home range throughout their lives. They have no way of knowing that a neighboring area is available and don’t want to leave their familiar home range.  This has had tremendous implications for management and how damage from deer can be reduced in a specific area.

The rebound effect – the hypothesis of increased fecundity of does when deer are removed from an area, i.e. if you remove deer they will have more fawns to compensate. This does occur in areas where the deer exceed the biological carrying capacity (BCC), meaning that the food supply is not sufficient for the deer population. In other words, the deer are not getting the nutrition they need, i.e. they are starving. The deer population has not exceeded the BCC in Ann Arbor, which is not to say that they are not causing environmental damage by exceeding the ecological carrying capacity. Above ecological carrying capacity, the rate of browsing is greater than the rate of food-plant regrowth.

See the University of Michigan’s Professor Chris Dick’s, The pseudoscience of non-lethal deer management for more information.

Opponents of lethal deer management also claim that culls and managed hunts present a danger to people and pets.  There is not a single example of such harm from all of the municipal or park system culls that have been done anywhere in the United States.

%d bloggers like this: