Which of the following best describes the change in coyote behavior in the presence of wolves?

Wolves play a very important role in the ecosystems in which they live. Since 1995, when wolves were reintroduced to the American West, research has shown that in many places they have helped revitalize and restore ecosystems. They improve habitat and increase populations of countless species from birds of prey to pronghorn, and even trout. The presence of wolves influences the population and behavior of their prey, changing the browsing and foraging patterns of prey animals and how they move about the land. This, in turn, ripples throughout plant and animal communities, often altering the landscape itself. For this reason wolves are described as a “keystone species,” whose presence is vital to maintaining the health, structure and balance of ecosystems.

1926-1995

ELK, no longer pressured by predatory wolves, became abundant and began to damage their own habitat. Having lost the fear of being hunted, elk gathered near streams, overbrowsing aspens, willows, cottonwoods, and shrubs that grow on banks and prevent erosion. Habitat for fish, amphibians, and reptiles declined as waters became broader, shallower, and warmer without shade from streamside vegetation. Elk populations were so out of control that park rangers began to kill and relocate elk in large numbers in an attempt to reduce their burgeoning population.

ASPENS seldom reached full height in Yellowstone’s northern valleys, where elk winter. Browsed by elk, the new sprouts and shoots were eaten, and existing trees were stunted. Along streams and around wetlands willows and cottonwoods were also not regenerating as effectively under heavy browsing pressure from elk. Fewer young trees meant songbirds lost nesting space. Beaver populations decreased as they rely on this vegetation to survive. At one point, only one beaver colony was living in the park.

COYOTES, no longer having to share the land with wolves, became much more abundant and one of the park’s top predators. But the coyote’s small size kept them from regulating the park’s large ungulate populations, like wolves do. Though coyotes will kill elk calves, they prey mainly on pocket gophers, voles, and other small mammals. They also specialize in killing the fawns of pronghorn. The lack of carcasses left behind by wolves reduced the food traditionally available for foxes, badgers, raptors, coyotes and other scavengers.

1995-Present

ELK, the primary prey of wolves in Yellowstone, have decreased in numbers within the park. Other factors such as drought, severe winters, and other large predators have also contributed to the decline in Yellowstone elk. But as wolves returned, the behavior of elk changed; elk became more vigilant and were once again forced to stay on the move. Vulnerable along the rivers and streams, elk now spend more time in denser cover or on higher ground with better vistas for spotting predators. Consumption of vegetation by elk is thus restrained, giving many riparian areas a chance to recover.

ASPENS, willows, cottonwoods, and other vegetation have in many places resumed their natural growth. When their favorite food and building material reappeared, beavers flourished, engineering broad wetlands that attract frogs, swans, and sandhill cranes. Stream banks once picked clear of vegetation and eroded by hooves erupted in wildflowers, which nourished insects, which in turn fed songbirds that nested among the thick willows. The water below now became shaded, deep, cool, and clear—a better habitat for aquatic-born insects and trout.

COYOTE numbers dropped as they once again share the land with wolves. Many coyotes were killed or driven away by wolves, helping to bring about a resurgence in pronghorn. A drop in coyotes leaves more gophers, and other rodents for foxes, raptors, and other mid-level carnivores.

WOLVES, now returned to their original habitat, play a vital role in keeping the world of predator and prey in balance. Once they’ve eaten their fill, the leftovers from their kills provide food for scavengers, including bald and golden eagles, magpies, coyotes, ravens, and bears.

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Wolves Strengthen Ungulates

Wolves cull sick, old and genetically inferior elk and deer, allowing the healthiest individuals to breed and perpetuate their species.

Wolves Feed Other Animals

The remains of a carcass left behind, unfinished by wolves, help feed grizzly bears, bald eagles, wolverines and many other scavengers.

Wolves Improve Riparian Areas

Wolves have redistributed the elk herds, allowing vegetation to recover along rivers and streams. More willows and aspens provide food for beavers. More beaver ponds benefit aquatic plants and animals. Shade from the trees cools the water, making the habitat better for trout.

Wolves Decrease Coyote Populations

Wolves kill coyotes, so rodent populations increase, benefiting struggling birds of prey. Also, with fewer coyotes, pronghorn antelope calves are less likely to be preyed upon.

The reintroduction of wolves to Yellowstone has attracted 150,000 new visitors each year, adding $35-million to the local economy annually.

On a quiet spring morning, a resounding “Slap!” reverberates through the air above a remote stream leading to Lake Yellowstone. Over much of the past century, it has been a rarely heard noise in the soundscape that is Yellowstone National Park, but today is growing more common-the sound of a beaver slapping its tail on the water as a warning to other beavers.

When the grey wolf was reintroduced into the Greater Yellowstone Ecosystem in 1995, there was only one beaver colony in the park, said Doug Smith, a wildlife biologist in charge of the Yellowstone Wolf Project.

Today, the park is home to nine beaver colonies, with the promise of more to come, as the reintroduction of wolves continues to astonish biologists with a ripple of direct and indirect consequences throughout the ecosystem.

A flourishing beaver population is just one of those consequences, said Smith.

A Yellowstone Beaver’s Tale of Elk

What happened, said Smith, is that the presence of wolves triggered a still-unfolding cascade effect among animals and plants-one that will take decades of research to understand.

“It is like kicking a pebble down a mountain slope where conditions were just right that a falling pebble could trigger an avalanche of change,” Smith mused.

So how did this avalanche of change work out for the beaver?

To answer that, you have to go back to the 1930s, when the wolf was killed off in Yellowstone. Even though Yellowstone elk were still preyed upon by black and grizzly bears, cougars and, to a lesser extent, coyotes, the absence of wolves took a huge amount of predatory pressure off the elk, said Smith. As a result, elk populations did very well-perhaps too well. Two things happened: the elk pushed the limits of Yellowstone’s carrying capacity, and they didn’t move around much in the winter-browsing heavily on young willow, aspen and cottonwood plants. That was tough for beaver, who need willows to survive in winter.

Healthier Willow Stands in Yellowstone

This created a counterintuitive situation. Back in 1968, said Smith, when the elk population was about a third what it is today, the willow stands along streams were in bad shape. Today, with three times as many elk, willow stands are robust. Why? Because the predatory pressure from wolves keeps elk on the move, so they don’t have time to intensely browse the willow.

Indeed, a research project headed by the U.S. Geological Survey in Fort Collins found that the combination of intense elk browsing on willows and simulated beaver cuttings produced stunted willow stands. Conversely, simulated beaver cutting without elk browsing produced verdant, healthy stands of willow. In the three-year experiment, willow stem biomass was 10 times greater on unbrowsed plants than on browsed plants. Unbrowsed plants recovered 84 percent of their pre-cut biomass after only two growing seasons, whereas browsed plants recovered only 6 percent.

With elk on the move during the winter, willow stands recovered from intense browsing, and beaver rediscovered an abundant food source that hadn’t been there earlier.

As the beavers spread and built new dams and ponds, the cascade effect continued, said Smith. Beaver dams have multiple effects on stream hydrology. They even out the seasonal pulses of runoff; store water for recharging the water table; and provide cold, shaded water for fish, while the now robust willow stands provide habitat for songbirds.

“What we’re finding is that ecosystems are incredibly complex,” he said. In addition to wolves changing the feeding habits of elk, the rebound of the beaver in Yellowstone may also have been affected by the 1988 Yellowstone fires, the ongoing drought, warmer and drier winters and other factors yet to be discovered, Smith said.

Yellowstone Wolf Trophic Cascade

Biologists are often faced with the grim task of documenting the cascade effects of what happens when a species is removed from an ecosystem, by local extirpation or even extinction. In Yellowstone, biologists have the rare, almost unique, opportunity to document what happens when an ecosystem becomes whole again, what happens when a key species is added back into the ecosystem equation.

“In the entire scientific literature, there are only five or six comparable circumstances,” Smith said. “What we’re seeing now is a feeding frenzy of scientific research.”

Scott Creel, an ecology professor at Montana State University, is hip-deep in that feeding frenzy.

“My research has been in the Gallatin Canyon,” said Creel, where elk inhabit four drainages. Wolves come and go, he said, enabling him to study what elk do in the presence and absence of wolves.

“Elk have proven to be pretty adaptable,” Creel said. “When wolves are around, they’re more vigilant and do less foraging.”

Elk move into heavy timber when wolves are around, Creel added, but return to the grassy, open meadows when wolves go away. Creel and other researchers are still working out what that means in terms of the elk’s diet and whether there are costs associated with this behavior.

Rather surprisingly, elk herd size breaks up into smaller units when wolves are around, said Creel, who had expected herd size to get bigger as a defense mechanism. “I think they’re trying to avoid encounters with wolves,” he said, by being more vigilant, moving into the timber and gathering in smaller herd units.

Yellowstone Wolves are Food Distributors

Researchers have also determined that wolves, in the recent absence of hard winters, are now the primary reason for elk mortality. Before wolf reintroduction, deep snows were the main determinant of whether an elk was going to die.

Researchers from the University of California at Berkeley determined that the combination of less snow and more wolves has benefited scavengers both big and small, from ravens to grizzly bears.

Instead of a boom and bust cycle of elk carrion availability-as existed before wolves and when winters were harder-there’s now a more equitable distribution of carrion throughout winter and early spring, said Chris Wilmers in the on-line journal Public Library of Science Biology. He added that scavengers that once relied on winter-killed elk for food now depend on wolf-killed elk. That benefits ravens, eagles, magpies, coyotes and bears (grizzly and black), especially as the bears emerge hungry from hibernation.

“I call it food for the masses,” said Ed Bangs, wolf recovery coordinator for the U.S. Fish and Wildlife Service. He said he was genuinely surprised by the vast web of life that is linked to wolf kills. “Beetles, wolverine, lynx and more,” he said. “It turns out that the Indian legends of ravens following wolves are true-they do follow them because wolves mean food.”