12 March 2005

(73) Wolves are social animals because of Ravens.


Study: Scavengers Make Dogs Social
By Jennifer Viegas, Discovery News

Sept. 14, 2004 — A 27-year study of wolves reveals that the carnivorous animals and their domesticated relatives, dogs, are social because food loss from ravens and other scavengers creates a need for packs, and packs promote socializing.

The paper, published in the current issue of Animal Behavior, also helps to explain why a domesticated cat is more likely to snub its owner than a domesticated dog.

In the wild, most small cats hunt tiny birds and other prey that leave few leftovers for scavengers. The pull of pack life for small wild and domesticated cats, therefore, is not as strong, the study suggested.

To obtain the wolf data, researchers studied wolves and moose at Isle Royale National Park, which is an island in Lake Superior where hunting is prohibited. There, moose are the primary source of food for the wolves. From 1971-1998, the scientists used fixed-wing aircraft to track the resident wolves and their moose kills.

The scientists determined kill rates per pack and how much food wolves and scavengers consumed. At most wolf sites, ravens were found to be the main scavengers. Anywhere from five to more than 100 ravens can show up where a wolf or a pack has killed prey.

John Vucetich, lead author of the paper and a research assistant professor at Michigan Technological University, and his colleagues detected and investigated 558 wolf-killed moose carcasses. The research team determined that packs of approximately six or more members each killed 4.5 moose per month during the study period.

While raven damage varies, this study and others indicate that wolves lose 4.41 to 81.57 pounds of food each day due to ravens. Such a loss is significant, because most individual wolves require just over 889 calories per day to maintain an average body weight of around 69.45 pounds.
Twenty to 30 percent of all wolf deaths are attributed to starvation.

Vucetich believes that packs allow wolves to maximize the meat from their kills because a greater number of wolves mean that more moose can be hunted with fewer leftovers. A pack also is better able to chase off ravens and scavengers, although ravens are tenacious and hard to deter.
Oddly enough, humans indirectly benefit from the ravenous ravens because Vucetich thinks pack life is linked to the social behavior of wolves, which led to domesticated dogs.

"The origin of a dog's social propensity may be wolves' solution to reducing the amount of food they lose to scavengers," Vucetich told Discovery News. "Reducing these food losses requires wolves to be social and well-behaved in social situations."

He added, "One reason wolves were domesticated, rather than say, foxes, is that they are social. Animals with an aversion to social situations are not easily domesticated and in this way, domestic cats are exceptional among domestic animals. So, dogs inherited the propensity to be social from wolves. It's a relic trait that humans maintain and exaggerate through breeding."

Douglas Smith, leader of the Yellowstone Wolf Project, agrees with the new study. He told Discovery News that he is involved in similar research at Yellowstone National Park in Wyoming. His data corroborates the Isle Royale National Park study.

"For example, it was vividly portrayed to me one day when I was observing a wolf (pack of six) and a cougar kill from the same viewpoint, a once-in-a-lifetime opportunity" Smith said. "The cougar was alone on the kill and trying to fend off every raven that came in, leaping in the air at the ravens. The cougar hated the ravens there because they were stealing food that the one cougar could not eat all at once."

Smith said the cougar wound up burying the carcass for later snacking, which resolved the problem for the time being. The wolves, on the other hand, managed to eat most of the carcass, which they left out in the open for the ravens. Meanwhile, the wolves took a nap nearby.

Both Smith and Vucetich's work could help to explain why some other carnivores that hunt large prey forage socially, while certain coyotes, feral and domesticated cats, and additional carnivorous consumers of smaller prey tend to be solitary hunters.

Despite the problems ravens can cause for wolves, Smith said humans are a wolf's biggest threat.
"We have had success with restoring wolves recently, but it is hard to get too optimistic given the future threats looming (such as habitat loss) and the fact that humans decide virtually everything for nature nowadays," he said. "Wolves have been public enemy number one for so long, it will be hard to wipe that history clean."