Gray wolves are apex predators that occupy a top niche in the natural food chain. Like bears and cougars, they have few competitors and play a prominent role in any ecosystem they inhabit.
Wolves’ primary prey is elk, deer, moose and other ungulates, although they also feed on smaller species such as mice, squirrels, rabbits, muskrats, marmots, grouse and even songbirds.
They also fight, kill or displace other top carnivores such as cougars, bears and coyotes. Studies have shown that the reintroduction of wolves can reduce coyote populations in some areas.
In these and other ways, wolves can change the dynamics of wildlife species across an entire ecosystem, altering predator-prey relationships and even the natural landscape. While they may contribute to declines in some species, wolves can also play an important role in the environment.
Wolves and ungulates
Wolves are selective hunters and tend to choose younger, older, and debilitated prey animals to increase their chances of success. In herds that have not been exposed to wolves for a time, this can increase the proportion of healthy animals of prime age in ungulate herds, leading to higher pregnancy and birth rates.
The removal of diseased animals can also reduce infection in the herd, although the presence of wolves can have the opposite effect by causing herds to gather more tightly to avoid attack. Excessive predation on younger animals can also offset the benefits of higher pregnancy and birth rates.
Drawing on a wide range of studies, the Washington Department of Fish and Wildlife (WDFW) developed a simple model of wolf predation that estimates that a single wolf kills an average of 22.6 to 33.5 ungulates per year to meet its dietary needs.
Based on that model, the estimated 100 wolves currently in the state can be expected to kill 2,260 to 3,350 ungulates – mostly deer and elk – per year. Those predation levels represent about 2 to 3.5 percent of the state’s elk population and less than 1 percent of the state’s combined deer population.
State wildlife managers have found no evidence that wolves’ current predation levels have had a discernible on Washington’s elk, deer or moose populations, most of which are growing or stable.
However, some western states have found that high concentrations of wolves can hasten the decline of some herds, especially those impacted by other factors such as harsh weather, poor habitat, high hunter harvest and other predators such as cougars and bears.
As Washington’s wolf population continues to grow, WDFW has expanded monitoring efforts to help understand the effect of wolf predation on state herds. The state’s Wolf Conservation and Management Plan provides WDFW with several options – including lethal measures – to protect at-risk ungulate populations from predation by wolves.
Throughout North America, wolves have shared habitat with cougars, bears, coyotes and other carnivores for centuries, often competing for the same prey. Most of their interactions take place at kill sites, where wolves usually have the advantage because of their pack behavior.
Cougars and wolves rely on the same main food sources, but have different hunting techniques. Wolves are coursing predators, running prey down, usually in packs. Cougars are stalking predators, ambushing prey as solitary hunters.
Reports from Yellowstone National Park and elsewhere suggest that cougars may avoid areas used by wolves or focus on different prey to avoid encounters with packs. This is also true for black bears, although grizzly bears usually prevail over wolves in a fight over a carcass.
Recent studies have found that the coyote population in Yellowstone National Park has dropped 39 percent since wolves were reintroduced in 1995. Grand Teton National Park reported a 33 reduction in coyotes. Less clear is whether wolves would have the same effect outside of national parks.
While wolves are highly protective of their kill, many other carnivores and scavengers benefit from the carcasses they leave behind. These carcasses may help to sustain large carnivores, wolverines, foxes, fishers, martens, raccoons, eagles, ravens and magpies, especially during winter.
By changing the dynamics of other wildlife species, wolves can also affect the vegetation and other characteristics of natural landscape. While there are few examples in Washington, land once overgrazed by deer, elk and other herbivores recovered once wolves returned to the area.
After wolves were removed from Yellowstone Park in the early part of the last century, the problem of overgrazing became so acute that herds of elk, pronghorn and bison were culled to protect the remaining vegetation. Since 1995, when wolves were reintroduced to the park, there has been resurgence of woody browse species in some areas such as willow and aspen.
Some scientists have suggested that a similar situation may exist in Olympic National Park, where extensive browsing by elk may have caused substantial changes in riparian plant communities. This, in turn, has been linked to riverbank erosion and channel widening, which reduce rearing habitat for salmon, steelhead and resident fish.
These examples may not be evident on a large scale across Washington because deer and elk populations are regulated through hunting. However, they do help to illustrate the prominent role wolves can play in nature.