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March 27, 2010 in Idaho
Elk reproduction woes tied to wolves
According to a recent study, in areas of high wolf density, extra-alert behavior reduces elk nutrition and leads to lower elk calf production.
(Full-size photo)
After hours of watching Yellowstone elk herds through a spotting scope, Scott Creel noticed a few interesting things.
When wolves appeared, the elk turned skittish. They spent more time on alert – heads in the air, ears pricked – and less time eating. They also left prime winter range to take cover in forested areas, where less food was available.
Even when wolves were nearly two miles away, the vigilant behavior persisted, said Creel, a Montana State University ecology professor.
Creel and fellow researchers linked the altered elk behavior to lower calf production. As their body fat drops, cow elk have difficulty staying pregnant through winter. They grow emaciated and abort, the research concluded.
The work helps answer questions about low elk calf numbers in some herds in Yellowstone National Park, said Creel, the lead author of a study that appeared last year in the Proceedings of the National Academy of Sciences. It indicates that wolves affect elk populations in subtle but important ways beyond direct kills, he said.
“If you look at the observed rate that wolves are killing elk calves, there are too many calves missing,” Creel said. “We can’t account for them all through direct predation.”
As wolves regain their role as top predators in the West, Creel said, the study could have broad implications.
“Those things elk are doing to avoid being killed may carry high costs,” he added. “We know that elk reproduction is affected by the severity of the winter. Wolves could be a complicating factor that makes it more difficult to maintain a pregnancy through a period when they’re losing body fat anyway.”
The research comes amid intense public interest in wolf-elk interactions. In Idaho, elk hunters and environmentalists engage in fierce debate over which factor played the greater role in the once-famous Lolo elk herd’s decline: worsening habitat or wolf kills. In Wyoming, state Fish and Game officials are trying to understand discrepancies in pregnancy rates among 4,000 elk that live in herds between the city of Cody and Yellowstone. Drought, disease and wolves are possible influences.
“It’s a complicated set of questions that people badly want to know the answers to,” said Arthur Middleton, a University of Wyoming doctoral student involved in the study.
Other studies by the National Park Service haven’t established a correlation between wolf-elk ratios and the proportion of pregnant adult cows. Creel said he couldn’t comment on other researchers’ work, but he said differences in study methods could have yielded different results.
Creel’s work is intriguing because it links wolves, habitat and elk nutrition, said John Cook, a wildlife researcher from La Grande, Ore. For the past 20 years, Cook and his wife, Rachel, have studied Western elk herds and how nutrition influences reproduction. Their work indicates that pregnancy rates drop off when a cow elk’s body fat drops below 9 percent.
But scientific understanding of how wolves influence elk behavior is in its infancy, Cook cautioned: “There’s an awful lot that’s not known.”
Cook and his wife surveyed Yellowstone’s northern elk herd during 2001, 2002 and 2003. Pregnancy rates and body fat were high.
“Those animals were in pretty darn good shape,” Cook said.
During a four-year period, Creel and his research team collected 1,205 scat samples from cow elk. The samples were taken after March 15, when pregnant elk would be in their third trimester. The scat was tested for progesterone, a hormone needed to maintain pregnancy. In areas with high wolf-to-elk ratios, progesterone levels in the scat decreased fourfold, Creel said.
In some other projects, the elk were tested for pregnancy in late fall or early winter. Creel said his method looked at whether elk were still pregnant later in the season, when the nutritional demands of the pregnancy are the highest, and food is typically scarce.
“This isn’t a new idea in ecology,” Creel said. “When a predator is in the system, it affects the system’s dynamics.”
Aquatic invertebrates retreat to colder, deeper waters to escape their prey. They grow more slowly in colder waters and produce fewer eggs, Creel said.
But less is known about large carnivores, he said. For the past 2 1/2 years, Creel has been working on similar studies with lions and hyenas in southern Kenya. Those studies examine whether the presence of lions and hyenas affects reproduction in their prey species beyond direct kills.
Closer to home, Creel said his work could shed new light on the intricate interactions of predators and their prey. Yellowstone wolves rely on elk for 85 percent of their diet.
As a result, the evolutionary pressure on elk to be good at detecting wolves is “pretty strong,” Creel said. Unfortunately for elk, “you can’t eat and do that at the same time,” he said.
Miners to return to Lucky Friday 
sbaran on March 27 at 5:27 a.m.
I find the title somewhat misleading. The population of every wild animal in Yellowstone waxes and wanes due to changes in the environment of Yellowstone. If the environment is changed the populations will change. Wolves have not been in the recent mix of animal populations in Yellowstone. They are now. One would expect the populations of the prey of wolves to decline in Yellowstone - or anywhere else wolves are reintroduced - and not just by direct wolf kills as the story mentions. One can also expect that Yellowstone elk populations have grown during the time wolves were absent from Yellowstone. Reintroducing wolves back into Yellowstone should decrease the elk population. Making it a headline and relating it to reproduction is dressing the obvious in somewhat inflammatory/sensitive rhetoric.
maria on March 27 at 8:34 a.m.
Well then, perhaps the Jackson Hole Elk Refuge should stop it’s annual legal hunt/cull. This article doesn’t tell the whole story. Back in the ‘70’s, thousands of elk in Yellowstone were exterminated by the park service because of overpopulation. The wolves were reintroduced to prevent this from happening again. You can’t have it both ways. I’ve lived and worked in Yellowstone and prey animals there are always on alert for any kind of predator. The issue of elk going into the forest to hide is arguable. I have a feeling Scott Creel didn’t leave the roadway much nor hike deep into the interior of the park for his study. The fires of 1988 opened up vast tracts of meadows that car tourists never see. The elk simply are not along side roads in the grass where they used to hang out. They don’t have to depend on the open meadows around the roadways any longer. You have to look for the elk but they are there and thriving.
omaha on March 27 at 9:18 a.m.
yeah maria, just discredit Scott Creel and say he was too lazy to leave the roadway.
maria on March 27 at 1:09 p.m.
I’d like to know exactly where he went then, omaha.
abee on March 27 at 1:35 p.m.
One of the issues discussed in the article is what is causing the decline of elk, wolves vs loss of habitat. As Steve said we are seeing an immediate impact on the elk now that wolves are present. We have caused this problem ourselves. These magnificent animals evolved together without our management for millions on years. My question is: who is the greatest predator of all?
lewis8457 on March 27 at 1:38 p.m.
I suppose they will start killing the wolves at yellowstone too. what are they supposed to eat huckleberries?
Mr_Bloggy on March 27 at 2:19 p.m.
Prey acting like prey. The horror.
notrich on March 27 at 8:36 p.m.
The article isn’t just “wolves versus habitat”, it’s also disease, weather such as snowfall and the amount of rain when feed is growing. How about poaching? Is there so little in yellowstone? Road changes or additions?
All the factors need to be taken into consideration and I think that was the point of the article – no enough information/data to make a good conclusion. So yes, the title of the article is misleading.
boognish on March 29 at 11:46 a.m.
“Aquatic invertebrates retreat to colder, deeper waters to escape their prey”
LOL. Nice editing. I hate it when animals escape their food.
bigsky on April 04 at 8:24 a.m.
creed and others have not shed new lite on what we have seen coming for a while in montana. the stress on the elk being chased all the time is going to have an effect on the reproduction. im relieved that the scientific community is now voicing their findings and not walking on eggshells as to not offend the environmentalist. another thing for you Daisey Pushers is to take into account, its not just the elk that are declining. the moose, muley deer and other species are taking a beating. other predators such as grizzlies, mountain lions, etc. are also on the decline due to the lack of prey or being chased off the kill by wolf packs. my tax dollars are now being spent on the re-introduction,monitoring the packs, monitoring the prey game (elk),etc..when the moose, mule deer, elk, bear, lions are all past the point of sustaining their numbers are the environmentalist going push to spend MORE of my tax dollars on recovery for them. its a big circle jerk and the environmentalist need to look at the long term. last is i have noticed most pro wolf folks are not in the states affected. the grizzly once roamed california (look at your state flag). lets reintroduce the grizzlies into their backyard.
loucas on April 29 at 7:08 p.m.
maria the elk in the park were killed in the 70s by the park service because people were not allowed to hunt them and then a article was published in the new york times telling of the “slaughter” of the elk in the park of the elk but did not tell that the elk were being taken and prosessed and fed to the poor. but the public was outraged so we stopped culling the elk population and they became over populated and now that the wolves are in the park they are at lower levels than before when we were manging them. wolves do not manage they kill till there is nothing left and they starve and move on or die
nowolves on July 26 at 8:38 p.m.
bigsky Do not walk on egg shells! There is a movement growing and growing….. people are starting to take more action and truly understand this poor excuse of an animal in Wisconsin. The more these radical environmentalist bring this high maintenance non-endangered non-threatened killer into areas that they do not belong the more people understand what the wolf is about the more the local people don’t like them. Our friends have seen wolves on and around the driveway their nieces use to go to the bus stop. They should not have to live with wolves that do not run like hell when they hear and see people. The longer they stay off the endangered list the greater the animosity we will have here in Wisconsin. It grows every time they kill livestock or someone’s pet! Only a matter of time before someone will end up dead like Candice Berner!