Cow Moose Pits Bull Against Bull

While speaking at a recent science conference, Terry Bowyer let out a groan that sounded like he had stomach pain. Bowyer, a professor at the University of Alaska’s Institute of Arctic Biology, was imitating the plaintive moan of a cow moose.

Two days later, I heard the same noise in the woods outside my house. I followed the cow’s voice until I saw her, walking a few steps ahead of a small bull in a grove of spruce trees and yellowed willows. Every few minutes, she bellowed like a milk cow in a pasture. Before long, the sound of snapping twigs from another direction indicated that another moose was approaching. I backtracked before it showed up, not wanting my nearby dog to bark and spoil the show.

The cow calls I heard were what Bowyer calls “protest moans.” He has heard them many times in Denali National Park and Preserve from September through November. After a four-year study there, he and two other scientists theorized that cows use a protest moan to spur competition between the bulls that court them.

“We heard many more moans when small bulls were among the cows,” Bowyer said. “Females foment competition—they egg on the males.”

Bull moose in Alaska gather harems, in which one male defends a group of females. During the four-year study, Bowyer, retired Anchorage biologist Vic Van Vallenberghe, and John Kie of the USDA Forest Service in La Grande, Oregon, hiked into the eastern end of Denali National Park and Preserve to observe groups of moose from 1987 to 1990. They watched 132 harems of mating moose. Each harem had an average of four females, which would sound off with a moan unique in the world of large game mammals.

“Elk don’t do it; reindeer don’t do it,” Bowyer said.

Bowyer and his colleagues first heard protest moans beginning in early September. The number of moans peaked in early October. After marking the time of a protest moan, the researchers noticed that bulls would become more aggressive toward nearby bulls in the following 30 minutes.

Cow moose are silent the rest of the year; their moaning in fall provides them a bit of control in selecting a mate, Bowyer said. In the world of Alaska’s moose, the most likely creature to pass on its genes is a bull moose with large antlers and bodies healthy enough to ward off smaller bulls. The mating season is tough on bulls; Bowyer showed a slide of an exhausted bull with a broken antler, perhaps soon to become victim of a grizzly bear.

A hunter in the audience at Bowyer’s talk asked him about the effectiveness of trying to duplicate a bull’s grunt versus a cow’s moan during hunting season. Bowyer said he thought learning how to groan like a cow moose would be a valuable skill for a hunter attempting to draw in a large bull.

“I would antler-rattle early and late in the season, and I would use cow calls September 15 and after (in the Interior),” Bowyer said. “You’re going to get a harem master if you use a cow call at peak times.”