Killing Wolves Can Increase Livestock Attacks

Disruption in pack social cohesion can free more wolves to mate, creating more mouths to feed in a tighter range,

A recent study came to a counter-intuitive conclusion: The more wolves killed to protect livestock, the greater the frequency of livestock attacks.

Washington State University wildlife biologist Rob Wielgus and data analyst Kaylie Peebles wanted to test the efficacy of lethal control programs used on predators. Such programs are commonly used to keep predator populations under control and livestock safe, but the scientists say, in a release, that they represent a "widely accepted, but untested, hypothesis."

The researchers found that with every wolf killed the chance of livestock attacks increases significantly. They noted that this probability trend line continues upward until 25 percent of wolves in a population are killed, at which point livestock depredation begins to level off.

Wielgus and Peebles write that such a level of lethal wolf population control "is unsustainable and cannot be carried out indefinitely if federal relisting of wolves is to be avoided." For the lethal control of wolves to result in the protection of livestock, then, the animals would wind up right back on the government endangered list.

The researchers studied 25 years of U.S. Fish and Wildlife Services lethal control data on wolves across Montana, Wyoming and Idaho. It turned out that with each wolf killed, the odds of sheep depredations rose 4 percent and for cattle deaths 5 to 6 percent in the following year. And, when 20 wolves were killed, they noted that livestock deaths doubled.

All of this, of course, begs the question why. How could killing more wolves result in more livestock deaths?

The researchers suggest that killing wolves probably disrupts the social structure of a wolf pack. When pack numbers decrease, particularly among alpha males and females that normally keep younger offspring from mating, more wolves are freed up to breed. That increases the number of breeding pairs. When those pairs have offspring, it results in more mouths to feed. And because the new parents are bound to one place, due to having pups, they can't hunt in as wide a range and may be more likely to hunt accessible livestock instead of seeking out deer or elk.

Wielgus and Peebles argue that while lethal control programs may sometimes be necessary in short-term situations, non-lethal programs -- such as guard dogs, horseback range riders, and use of "risk maps" ranchers can consult to keep livestock clear of wolf-rich areas -- should also be considered. To underscore his point, Wielgus said his Large Carnivore Lab monitored 300 sheep and cattle in Eastern Washington's wolf country over the summer and none of the animals were killed by wolves.

"The only way you're going to completely eliminate livestock depredations is to get rid of all the wolves," Wielgus said, "and society has told us that that's not going to happen."

The study has just been published in the journal PLOS ONE.

June 29, 2012:

Predators are both icons and targets. Idealized as symbols of strength and bravery, they are also hunted mercilessly. This duality is exemplified in California's state flag which prominently features the grizzly bear (Ursus arctos horribilis), although the last bear in California was shot in 1922. All is not lost for North America's persecuted predators. Several carnivorous species are beginning to recover slivers of the territory they lost to Western civilization, but as their populations grow, so too do their interactions with humans and livestock. Some of these conflicts and contacts have drawn media attention. This month in Montana, a mother grizzly and her cub had to be relocated after mama bear took down approximately 70 sheep over a two week period. In one night the insatiable ursine mom killed 58 sheep, reported the Great Falls Tribune. In Yellowstone, America's most famous population of grizzlies may have reached the maximum the park can support. The population in the core area of Yellowstone grew by four to seven percent from the 1980s to the early 2000s, but has leveled off at around 600 for the past few years, reported the Wyoming Star-Tribune. But the bears may not be welcome outside of the park. "The bears in the Yellowstone area are filling up their logical habitat," Steve Schmidt of the Idaho Fish and Game Department said in the Missoulian. "We also believe as a committee that bears have met or exceeded their social carrying capacity. The public appetite for further expanding this bear population is very small. And the political appetite is nil." Grizzlies once ranged from the Arctic as far south as Mexico and roamed the Great Plains, but by the mid-20th century they had been reduced to only Canada and Alaska with a tiny remnant population in the lower 48 states. Yellowstone National Park is now the furthest south that the bears live.

Gray Wolves

Like the grizzly bear, wolves once ranged over most of North America. Gray wolves (Canis lupus) were Earth's widest ranging land mammal until the rise of Homo sapiens. By the 1950s, the wolf had nearly disappeared from most of the lower 48 states of the U.S., though populations remained strong in northern Canada and Alaska. In 1995, Canadian wolves were captured and reintroduced into Yellowstone National Park in northwest Wyoming. The wolves thrived in the park. The return of the wolf packs balanced the area's ecosystem because the howling hunters chowed down on the overpopulated elk that were devouring too much vegetation. All those tasty elk did the trick and the wolf population grew from a founding group of 68 in 1995 to 98 at the end of 2011, according to the National Park Service. In other parts of the increasingly wild West, wolves rebounded as well. Now, approximately 1,774 wolves roam Idaho, Montana and Wyoming. The predatory packs had been protected until last year, when Congress ordered the wolves removed from the Endangered Species List. Although this caused outrage, a group of wolf advocates decided not to appeal the case to the Supreme Court earlier this month, according to the Seattle Post Intelligencer. Other wolf species face fiercer foes than legislators. Two packs of highly endangered Mexican gray wolves are threatened by the intense wildfire raging in New Mexico, reported the Christian Science Monitor. The species was extinct in the wild until captive bred wolves were released in New Mexico and Arizona in 1998. There are now approximately 50 wild wolves roaming the Southwest.


Pumas -- also known as cougars, mountain lions, and panthers -- once prowled from central Canada to the tip of Argentina and from the Atlantic to the Pacific. The big cats still prowl much of their range, but were exterminated in most parts of North America east of the Rocky Mountains. Where the cats still live, attacks are rare but brutal. An estimated 4,000 to 6,000 cougars live in California, but since 1890 there have been only six fatal attacks, according to the San Francisco Chronicle. The last fatal attack in the U.S. was in New Mexico in 2008. The low probability of a fatal attack doesn't reduce the fear Midwesterners may feel now that mountain lions are returning to the region. A recent study in the Journal of Wildlife Management documented the cougar comeback. Between 1990 and 2008, there were 178 confirmed cougar sightings in Midwestern regions where the cats had previous been mostly eradicated. The pumas pounced on Nebraska the hardest, with 67 sightings, reported the Omaha World-Herald. Some cats made it as far as Connecticut, 1,500 miles away. So far most of the meandering mountain lions are believed to be restless males wandering hundreds of miles in search of mates. If females start to spread as well, the cats could return anywhere there is enough prey, such as deer. Perhaps nature will soon provide the solution to the suburban deer that regularly devour homeowners' gardens and landscaping.

Black bears

Of all the large carnivores making a comeback, the black bear (Ursus americanus) is the most likely to be found napping in the basement waiting for the TV repairman. A baby bear might even be hanging around the garage until mama bear comes along to let it out. If a bear gets bored of chilling out in suburbia, it can always hitch a ride downtown. Black bears once lived in most forested areas of North America, but the bears' territory shrank as cities and farms expanded. But this bear isn't rare. There may be as many as one million black bears, mostly in the U.S. and Canada. Beware of the bear! Although not as territorial and defensive as its massive cousin the grizzly, black bear attack are on the rise as humans push further into the bears' domain. Wild bears killed 63 people over the past 110 years, according to a study in the Journal of Wildlife Management, and the rate has been increasing since the 1960s. Recently, three bears were shot in Arizona after a string of attacks, reported the Payson Roundup. Officials believe the bears may have resorted to raiding human habitations because the animals were having a hard time finding food due to the drought in the region.


Not all deadly predators are huge beasts. Some hide beneath piles of leaves, or look like a stick in a Wal-Mart garden center. This year an above average number of venomous fangs have been sinking into human flesh. The warm winter leading into an early spring made 2012 perfect for cold-blooded creatures. California's snakebite tally for April and May, 129, is nearly double last years' count of 70. In Texas, two undocumented immigrants from Guatemala were bitten by rattlesnakes. Border patrol agents found them and took them to a hospital where they are expected to recover, reported Valley Central. Besides being caught and deported, those men were lucky. Untreated snake bites can be deadly, like the recent death of a snake-handling Pentecostal preacher bitten by one of his serpents. On the whole, humans aren't usually in harms way of these predators. Snake bites kill an average of 6 people per year in the U.S., according to the University of Florida. An American is nine times more likely to die from a lightning strike than a rattlesnake's strike. On the other hand, some people make a sport of slaughtering serpents. In Sweetwater, Texas, the annual Rattlesnake Round-up draws upwards of 30,000 spectators calling out for cold-blood. In 2003, hunters brought in 4,207 pounds of rattlesnakes to be put on display then massacred. Several other cities, such as Opp, Georgia, have round-ups as well. Conservationists have protested such events, stating that eastern diamondback rattlesnake (Crotalus adamanteus) numbers are declining and that the way they are treated is animal abuse, reported the AP.

Bald Eagle

The rattlesnake was once a symbol of the United States, warning enemies, "Don't tread on me." Another symbol of the States, the bald eagle, had some hard times, but is now back on the branches of America's forests. The eagle plunged from a population in the hundreds of thousands in the 18th century down to only 412 nesting pairs in the lower 48 during the 1950s, though populations in the far north remained strong. Thousands of eagles were shot. Thousands more were unable to reproduce after the insecticide DDT made their eggs too brittle to survive. Strict enforcement of hunting bans and outlawing DDT saved the eagles from disappearing from the land they represent. Once conditions improved, the eagles made a comeback. June 28th was the fifth anniversary of the eagle's removal from the from the Endangered Species list. The species' population is now estimated at more than 100,000. Today's go-getter eagles can even handle the hustle of city life. More than a dozen bald eagle nests can be found within the Chicago metropolitan area, reported the AP. Some bald eagles still need a hand from humans. In May, two bald eagle chicks fell from their nest near Boston, Massachusetts and were taken to a wildlife rehabilitation center. One day before the anniversary of their species' removal from the endangered species list, the birds were set free, reported CBS News Boston.


Some predators never had anything to worry about when Western civilization started encroaching on their domain. Coyotes may have suffered somewhat from bullets and traps, but they benefited from having their main rival and threat, the wolf, taken out of the picture by humans. Coyotes were once limited to western North America from Alaska to Panama, but now live virtually everywhere in North America. Coyotes have adapted to the suburbs and can even become city-dwellers. An Ohio State University study estimated that 7,000 wolves live in the metropolitan Chicago area. One consequence of living close to humans is the tendency of coyotes to mate with domestic dogs. The “coydog” offspring have the coyote's wild instincts, but lack their fear of humans. Coyotes don't play coy with wolves either. Many of the canids in New England and eastern Canada may be descendants of hybrid coywolves. The group has formed its own distinct population, called eastern coyotes. A Canadian folk singer, Taylor "Mitchell" Luciow, was killed by coyotes that wildlife managers suggest may have been this larger more aggressive eastern breed, reported National Geographic. Luciow' s death was the first and only known killing of an adult human by coyotes. A recent string of three attacks on humans by coyotes was out of character for the normally shy pure-breed coyotes. The attacks all occurred within a 10 day period. Two attacks injured women in California, reported ABC News. Then a 5-year-old girl was jumped upon and nipped by a coyote in Oregon, but received only scratches. Officials believe that the drought prevailing over much of the U.S. may have made the coyotes agitated and sent them searching for food and water in unfamiliar territory.