September 10, 2021
By Dr. James C Kroll "Dr. Deer"
The first deer-like species appeared in tropical Asian forests about 24-25 million years ago, during the Miocene period. From these ancestors, deer radiated east and west into Eurasia and North America. The first whitetails appeared along with mule deer and blacktails around 4 million years ago.
The Pleistocene period, 1.8 million years ago, was the “Golden Age” of mammals, and gigantism was present in almost every mammalian genus. Giant sloths, rhinoceros, mammoths, antelope and a host of “megafauna” existed at that time. Along with them, extremely large predators co-evolved to take advantage of the large packages of protein.
Then the world changed dramatically during the last “global warming” cycle, significantly altering Ice Age habitats. By 12,000 years ago, at least 90 genera of these large mammals became extinct; and along with them some 8 of the estimated 23 species of mega-predators.
By the time the first western settlers came to North America, deer predators included only a small handful of species. Among them were wolves, bears, mountain lions, coyotes and bobcats. As you will learn below, each of these developed specialties in predation on deer.
My own research and experience have taught me that predation should be thought of in terms of a “suite of predators.” Each predator (when present) contributes additively to deer mortality. Let’s discuss the suite of predators currently counted as significant or potentially significant killers of deer.
By the 1980s, coyotes had advanced into South Carolina, catching a lot of deer managers by surprise! Southeastern deer biologists reported a 36 percent decline in deer populations by 2006. Of course, not all of this decline can be directly attributed to coyotes, but I am positive they do have a significant effect.
By 2000, coyotes were fully established in the Northeast, with Pennsylvania biologists reporting them to be a significant predator of whitetails, especially in the early months of life.
Coyotes are opportunists that tend to focus on sick or wounded deer in the warm season, but they do take advantage of deep snow to capture and kill healthy deer. Yet their real specialty is killing fawns! They have the uncanny ability to learn where and when fawns are being born, then move into such areas until fawns become more difficult to capture.
Researchers report coyotes are responsible for a total mortality impact of 9-50 percent of fawns. Studies show that heavy coyote control can increase deer populations; however, one study in Southeast Texas showed coyote removal increased fawn survival, but did not change deer population density. However, at the time, deer populations were very high in that region, and recruitment was quite low, due to nutrition.
A best management practice for dealing with coyotes is heavy trapping prior to the fawning period. Combined with efforts to control deer herd sex ratios to reduce the total duration of the fawning period, it’s possible to overwhelm coyotes’ efforts to kill fawns.
Black Bear populations have been on the increase for over 20 years. Population estimates range from 850,000 to one million. My personal experience and research support that estimates of black bear populations are very conservative, as much as tenfold in some areas.
Black bears are the most specialized of deer predators, and they focus mostly on fawns. Remember, a black bear can smell about 400 times as well as a blood hound. The frequently used “fact” that fawns do not have scent is totally false! I personally have watched bears go into a search pattern in large food plots, picking up the scent of hidden fawns and quickly killing them.
Studies on black bear predation in Minnesota, Pennsylvania and Louisiana report fawn mortality as high as 50 percent. Yet, habitat can be a significant factor. A Pennsylvania study examined fawn mortalities in agricultural and forest landscapes, finding higher predation in forest habitats.
Within the last 20 years, I’ve received countless reports of mountain lions in places where they had not been seen in over 100 years. For some time, state agencies tended to downplay such sightings as mistaken identity or an aberrant sighting; yet, the advent of trail cameras and some scientific studies clearly show lions are on the rebound.
Most biologists agree mountain lions are moving eastward, and there is plenty of room and prey to support this movement. Officially, lions are listed for 16 western states and Florida. However, current data support lions in about twice as many states.
Lions occupy another niche in the suite of whitetail predators. They kill mostly adult deer and have been shown to be “trophy hunters,” meaning they will favor bucks over does. I believe the reasons for this are simple. Bucks are larger as a food source, are often alone, and will stand and fight in hardened antlers! Those factors subject bucks to higher predation rates.
Female lions will kill one to two deer a week when with kittens, and male lions will kill about one deer per week. The overall impact of lion predation on deer obviously is a function of the number of lions present. Current estimates of lion populations are somewhere between 19,000-24,000 in the U.S.
Hunter mortality for lions has been estimated at about 9 percent annually, well beneath growth potential. I predict lions will become a significant deer predator in the coming years.
The most charismatic of deer predators, wolves are the focus of recent controversies regarding elevating them to game animal status. A recent wolf season in Wisconsin even resulted in all-night candlelight vigils by anti-hunters! Yet, wolves probably have been the most significant predator of deer since the Pleistocene.
Research has shown that wolves are tremendously efficient in killing deer, and packs can have a devastating impact on deer populations. It is my belief that wolves helped develop the tendency of deer to find “sanctuaries” in habitats to avoid detection; a preadaptation to sport hunting.
Reliable scientific studies support that, where wolves are prevalent, deer can be found only in the interstices of wolf territory boundaries. This is because wolves respect pack boundary lines in an effort to avoid conflict.
Recently, research in the Yellowstone Country has shown wolves to be a significant predator to mountain lions; seeking out dens and killing the lion cubs. This is an ironic twist to the predation suite discussed to this point.
Bobcat populations also are increasing; however, I view them as minor players in the deer predation game, when compared to the above species. On occasions, I have experienced kills of mature deer and fawns from bobcats, but not on par with the other predators.
I did have a 3 1/2-year-old buck killed by a large male bobcat. But they are considered mostly as fawn predators, with impacts ranging from 2-20 percent of deer mortalities. Individually, they probably do not affect deer populations, but when added to the impacts of the other predators, this still could be significant!
The increase in predators over the last two decades is mostly due to changing public opinion and changing land-use. Published studies on predator impacts, unfortunately, focus on a single species’ impact, compared to other causes for mortality, including hunting. Yet, the impact of mortality agents generally are not compensatory, but additive!
When you couple this with a lack of data on distribution and numbers of most predator species, you can see why wildlife agencies often fail to factor in predation in making management decisions about deer. This especially is true when these agencies encourage population growth of predator species, that either are long eradicated or rare in numbers.
Furthermore, currently, there are a host of other mortality agents working against deer populations. These include hemorrhagic diseases, habitat degradation, winter severity, automobile accidents and competition from other herbivores.
Given these complex limiting factors, the days of generous doe bag limits may be coming to an end! But before management decisions are made regarding hunter harvest, we must consider all factors affecting deer populations, including the impacts of all members of the deadly suite of deer predators.
About the Author
Dr. James C. Kroll is the founder and director of the Institute for White-tailed Deer Management & Research in Nacogdoches, Texas.