Study: Wolves aren’t affecting elk nutrition, weight

LAURA LUNDQUIST, Chronicle Staff Writer

Posted: Tuesday, June 11, 2013 

 

Wyoming researchers have concluded that while wolves may eat elk, they don’t necessarily cause elk other detrimental effects, such as weight loss.

In the last of three studies from the University of Wyoming and the Wyoming Game and Fish Department, scientists found that migratory elk in wolf-occupied areas didn’t have worse nutrition or less body fat than other elk, a conclusion that contradicts some recent research from the greater Yellowstone ecosystem.

Between 2007 and 2010, biologists put GPS collars on 70 elk in migratory and resident herds, as well as a few wolves from four packs that resided in the same area. Using the GPS data, the scientists could record when the wolves came close to the elk and how the elk moved when wolves were near.

The researchers recaptured some of the collared elk and measured their body fat and pregnancy rates in March of each year, right before they’d have their fawns.

Predation has a direct effect on elk population, but some research, including studies by Montana State University biologist Scott Creel, suggested that wolves cause elk to change their feeding behavior so that they didn’t eat as well.

When predators are around, Creel suggested that ungulates tend to be more vigilant and sometimes move into more wooded areas where forage isn’t as plentiful. The result would be elk cows with less body fat that produced fewer or weaker fawns.

Creel’s analysis was more indirect in some cases, relying on analyses of elk feces and tissue samples.

In contrast, Arthur Middleton, author of the Wyoming study, said his study used direct measurements of interactions between specific animals. As a result, the Wyoming data indicated that wolves don’t find elk that often, and when they do, the elk don’t remain wary for long.

Migratory elk wintering in central Wyoming, where wolves are more plentiful, had close encounters with wolves about every nine days. Resident herds in eastern Wyoming, where wolves are rare, dealt with wolves every 50 days.

Elk didn’t change their behavior until wolves were less than a mile away. On average, wolves stayed within that range for about five hours.

Once the wolves left, elk returned to normal foraging behavior within 24 hours.

In the migratory herd that ran into wolves more often, the late winter body-fat measurements were no lower than those in the almost predator-free resident herd.

The researchers concluded that, outside of killing elk directly, the impact of wolves on elk reproductive success was insignificant.

The authors also suggested that there’s a difference between elk reaction to ambush predators, such as mountain lions, and reaction to active hunters, like wolves, which only come along once in a while.

Elk may learn to associate certain types of habitat with mountain lions and be wary at all times while in that habitat. But active predators can hunt anywhere, so elk have no clues as to where they should be wary.

Also in open range, elk can use defensive group behavior, such as bunching together, so they don’t have to be constantly on the lookout.

The authors had previously concluded that climate change and direct predation by bears and wolves have more of a detrimental effect on migratory herds in Wyoming.

Creel said his work suggested that elk respond to wolves and that Middleton’s data found the same thing. Creel said his studies were different because he was observing elk herds in the Gallatin Canyon, where habitat patches are smaller and elk aren’t roaming in larger herds through wide landscapes.

“For there to be differences is not surprising,” Creel said.

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