The arrival of the eastern coyote in the Northeastern United States and Maritime Canada has had a profound impact on the wildlife ecology of the region.
For 30 years (1975-2005), I served as the deer management and research biologist for the Maine Department of Inland Fisheries & Wildlife. During that tenure, we struggled to maintain viable populations of white-tailed deer in the face of major habitat changes and the presence of a new deer predator, the eastern coyote.
After gray wolves died out during the late 1800s in the Northeast, Maine lacked a canine predator that could efficiently kill white-tailed deer. Wherever hunter access was good, deer populations could be held in check with our either-sex (buck or doe) hunting seasons. Where hunting access was poor, as in the big woods of northern and eastern Maine prior to the 1970s, deer populations were more difficult to manage.
Between the 1880s and early 1960s, deer in the northern half of Maine experienced several cycles of extreme abundance, followed by crashes to low numbers caused by over-browsing and subsequent starvation during severe winters.
Since the 1960s, deer populations in the northern half of Maine have been steadily declining, due to two additional mortality factors not present earlier: predation by coyotes and degradation of wintering habitat. Even in the more deer-friendly central and southern parts of Maine, deer mortality increased with the arrival of the coyote.
Coyotes are not native to Maine or to the Northeast. Into the vacuum created by the disappearance of gray wolves, coyotes began to migrate across the northern tier of Midwestern states and adjacent parts of Canada. Along the way they evidently interbred with remnant populations of wolves. Hence, eastern coyotes are mostly coyote but also part wolf, genetically, physically, and behaviorally. At 25 to 50 pounds, eastern coyotes are larger than their western cousins, their family groups tend to stay together longer during the year, and they are more efficient deer predators.
Mainers began encountering coyotes in the 1950s, and coyotes existed statewide at peak numbers by the late 1970s. Southeastern Quebec got coyotes slightly earlier, while New Brunswick and Nova Scotia were colonized somewhat later.
Unlike the much larger gray wolf, coyotes thrive on smaller prey during part of the year in Maine. Being a mid-sized carnivore gives them a distinct survival advantage. They can efficiently prey on mice, songbirds, turkeys, snowshoe hares, raccoons, beaver, fawn and adult deer, and pet cats and dogs if the opportunity arises. They also dine on fruits and carrion. Such flexibility in acquiring its groceries enables the coyote to thrive almost anywhere in Maine.
During the past 40 years, coyote predation on deer has been researched extensively by state, provincial, and federal fish and wildlife agencies, as well as universities, here in the Northeast. There are two excellent reviews of coyote/deer research available. One is “Eastern Coyote: The Story of Its Success,” a 1995 book by Canadian wildlife biologist Gerry Parker. A 2008 scientific report (CFRU Research Report RR-08-02) was produced by wildlife biologists Pete Pekins and Matt Tarr for the Cooperative Forestry Research Unit at the University of Maine. It is a critical analysis of the winter ecology of deer in northern Maine deer wintering areas.
It has been widely stated that coyotes only kill old, weak, or sick deer, thus culling the herd of unfit animals that would soon die anyway. Eastern coyotes do take any unfit deer they encounter, but research has shown conclusively that they are also very capable of killing healthy deer under several, sometimes common, conditions.
Coyotes can prey on any deer in deep snow. A deer chased into two feet or more of snow soon flounders, and becomes dinner for coyotes regardless of its physical condition. Snow depths exceeding two feet are the norm in northern Maine for weeks on end. In central and southern Maine, deep snow occurs less frequently and for shorter duration, but it still enables coyotes to readily kill deer.
Glare ice on lakes, ponds, and streams also helps coyotes kill deer regardless of physical condition. Deer hooves offer little traction on glare ice; coyote claws do. Deer fall, cannot get back up, and become easy prey. Since nearly all Maine deer wintering areas occur along waterways, these conditions can be commonplace.
The quality of deer wintering habitat also influences coyote predation. Deer seek out dense, tall, mature evergreen forests in winter because the thick overhead canopy shelters them from the wind, provides food, and reduces the snow depth underneath so efficiently that it is typically half that in open areas or hardwood forests. Widespread tracts of mature evergreen forest allow wintering deer to create an extensive trail system that aids in both finding food and escaping predators.
Disturbances that fragment these forests, reduce their size, or excessively thin the canopy, result in deeper snow, reduced foraging ability, and higher losses to coyote predation and malnutrition.
During the past 40 years, northern and eastern Maine conifer forests have been extensively altered by spruce budworm infestations and by logging. Many forests that once sheltered deer can no longer do so. Others forests remain, but in less than optimum condition. A few forests still provide high quality deer yard habitat, but coyotes can kill some deer even here. Coyotes can hold deer numbers below what any habitat can sustain.
Severe winters also greatly affect deer survival. Long winters with prolonged cold and deep snow take their toll.
Too often deer are losing a race against time. All winter they subsist on poor quality foods and continually lose weight. Deep snow that restricts them to trails makes finding adequate food difficult.
After 10 to 12 weeks of severe nutritional deprivation, death by malnutrition becomes evident. Fawns and mature bucks are usually the first to die; mature does are the most resilient.
Losses to both malnutrition and coyote predation inevitably increase during severe winters. Because coyotes can prey on healthy deer in deep snow, winter deer losses are typically higher when coyotes are present. In other words, deer losses to coyotes don’t merely replace starvation losses; to some degree they add to them.
Coyotes also sometimes kill adult deer during snow-free months. Some of this predation occurs in spring, when winter-weakened deer are moving onto summer range. Other losses occur during summer and fall, when most deer should be in good physical condition. It is probable that cooperative hunting by two or more coyotes, another wolf-like trait, tips the scales in the coyotes’ favor.
Eastern coyotes also target newborn deer fawns, which are relatively defenseless and often occur in predictable habitats. Coyotes, along with black bears, bobcats, red fox, fishers, and feral dogs, may collectively have a profound negative impact on fawn survival.
Maine’s Inland Fisheries and Wildlife Department does not routinely estimate how many deer are lost annually to coyotes in Maine. That number undoubtedly varies, yet the addition of this new predator has definitely added to herd losses, not merely replaced others.
In a 1995 report to the Maine Legislature, I estimated that the statewide deer herd numbered about 200,000, and roughly 22,000 were lost to coyotes. Whenever a single mortality factor approaches 10 percent of the deer population, given all the other mortality that deer experience, deer managers need to take notice.