Strength in Numbers? For Wolves, Maybe Not says USU Researcher
Thursday, Sep. 29, 2011
Wolves pursue an elk in Yellowstone National Park. Research by USU ecologist Dan MacNulty challenges the popular belief that wolves are highly cooperative hunters. Photo by Dan Stahler, National Park Service.
Research by Dan MacNulty, assistant professor in USU's Department of Wildland Resources, appears in the September-October 2011 issue of 'Behavioral Ecology.’
Watching a pack of wolves surround and hunt down much larger prey leaves most people with the impression that social predators live in groups because group hunting improves the odds of a kill. But according to findings by Utah State University wildlife ecologist Dan MacNulty, that explanation may not tell the whole story.
“Surprisingly few studies have tested whether hunting success actually increases with group size,” says MacNulty, assistant professor in USU’s Department of Wildland Resources.
He and colleagues Douglas Smith of the Yellowstone Center for Resources, David Mech of the U.S. Geological Survey’s Northern Prairie Wildlife Research Center, John Vucetich of Michigan Technological University and Craig Packer of the University of Minnesota explored this idea using modern statistical techniques and direct observations of individually known wolves hunting elk in Yellowstone National Park. Their findings appear in the September-October 2011 issue of Behavioral Ecology.
“What we discovered is that hunting success increased with groups up to four wolves then leveled off,” says MacNulty, who has been involved with the Yellowstone Wolf Project since its 1995 inception. “In groups of more than four, we observed that individual hunting effort decreased.”
While wolves are often portrayed as invincible predators in popular culture, they’re extremely vulnerable when pursuing large mammals.
“Hunting large prey is dangerous,” says MacNulty, who has observed wolves kicked, gored and stomped to death by elk and bison. “For that reason, wolves are very cautious hunters. There’s a lot of incentive to ‘hold back’ and let others go in for the kill.”
Part of what determines a wolf’s willingness to engage in the most dangerous tasks of hunting is the individual’s size, age and hunting ability. Wolves reach their physical peak around three to four years of age. What also determines a wolf’s willingness to mix it up is how much the animal has at stake.
“As you might guess, parents generally take the lead because they have offspring to provide for,” he says.
But even in groups of able-bodied breeders, effort declines when more than four canids join the hunting party.
“It makes sense to look out for number one,” MacNulty says. “Given a choice, wolves will stay out of harm’s way until it’s safe to enjoy the spoils of the hunt. They’re opportunists. And this challenges the popular belief that wolves are highly cooperative hunters.”
He says abundant evidence points to similar patterns with many other animals, ranging from such diverse species as spiders to chimpanzees.
“Hunting success also peaks in small groups with other social predators,” MacNulty says. “But our study is the first to rigorously test this pattern and demonstrate it’s likely due to individuals switching from cooperation to ‘free riding’ as group size increases. Our study also suggests that social predators live in large groups for reasons unrelated to group hunting success.”
The team’s findings also offer insight into wolves’ behavior and their patterns of predation, he says. Such findings may assist efforts to prevent conflicts between wolves and livestock.
“Wolves are risk-averse,” MacNulty says. “Management that takes advantage of this behavior may be an effective way to reduce wolf predation on livestock.”
Related links:
- “Science Shot: Freeloading Wolves,” Science Now, AAAS
- “USU Professor Publishes Study on Hunting Behaviors,” Standard-Examiner
- USU Department of Wildland Resources
- USU College of Natural Resources
- USU Ecology Center
Contact: Dan MacNulty, 435-797-7442, dan.macnulty@usu.edu
Writer: Mary-Ann Muffoletto, 435-797-3517, maryann.muffoletto@usu.edu
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Wolves will kill for more space,
new USU study finds
new USU study finds
By Amy Joi O'Donoghue
May 17th, 2014 @ 8:16pm
Dan Stahler, National Park Service
Amy Joi O'Donoghue
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LOGAN — Having your own space not only brings peace of mind, but it also correlates strongly to a greater chance of survival for wolf families at Yellowstone National Park.
A new study involving Logan's Utah State University and University of Oxford found wolves will fight to the death to protect their turf if they lack adequate space to raise their pups.
The aggressive behavior of families looking out for their own is not limited to wolves, or the wilds of nature, said researcher Dan MacNulty, a USU ecologist and assistant professor in the Department of Wildland Resources.
"These family groups of wolves that are competing with each other for space and resources. That is not unlike humans," he said. "It is well-demonstrated that chimpanzees will compete and war with each other over space and resources and certainly humans are known to do so, if in a more sophisticated way."
The study, published in the online issue of the Journal of Animal Ecology in the British Ecological Society, followed 280 collared wolves in northern Yellowstone for 13 years.
"This study produced a generally novel result because the conventional thinking is that large carnivores are limited by the abundance of prey in a given area," MacNulty said. "But what these wolves are ultimately limited by is the amount of space they have to raise their pups in safety."
Wolves killing wolves is their No. 1 cause of death in Yellowstone and MacNulty said the research showed that adult survival rates dropped below 70 percent if there were greater than 65 wolves per 1,000 square kilometers.
This study produced a generally novel result because the conventional thinking is that large carnivores are limited by the abundance of prey in a given area. But what these wolves are ultimately limited by is the amount of space they have to raise their pups in safety.
–Dan MacNulty, USU ecologist
These key observations in wolf infanticide may provide helpful lessons for management of wolf populations because of the insights they deliver, he said.
"For those concerned about wolf populations, even when you have super abundant prey like in Yellowstone, there are limits to wolf population growth. There is an intrinsic limit to the number of wolves that occupy a given space," MacNulty said, adding that because rival packs will attack and kill rival wolf pups, their numbers are self-limiting.
"What this paper does say is, though there is this notion that wolves will increase like a locust without any sort of natural limit, that idea is not supported by the data," he said.
MacNulty, who has been studying the wolves at Yellowstone for 19 years, said the rivalry among wolf families ramps up despite ample food when they are packed in too closely to one another.
"One of the things everyone needs to realize is that these wolf packs are not random collections of individuals," he said. "They are packs led by parents, with the offspring of the current year and preceeding years, often with aunts and uncles who are related to the breeding male and females. … More wolves meant more fighting and killing. As a result, survival rates declined as wolf density increased.”
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1 comment:
That's interesting; I've read/heard the same thing with hunters using dogs to bay large, dangerous game(bears, boars, lions, etc.), that have come to the exact same conclusion--more than 4 in a pack, and they just get in each others' way!....L.B.
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