Alaska study finds female moose manipulate males to fight

Moose-mating season, just around the corner in Alaska, means crisp fall days, ripe berries on the bushes and, according to a new study, animal behavior that might seem more at home in a rowdy singles bar.

Female moose may be able to manipulate amorous males - inciting fights between male competitors by moaning. The ability of the cow to manipulate amorous males into Denali National Parkfighting each other allows the more desirable bulls to emerge as mates, according to the study, which is based on observations of a team led by Dr. Terry Bowyer from Idaho State University in Alaska's Denali National Park (right) and Preserve, Alaska.

The cows' efforts are subtle, so they have long been overshadowed by the belligerent, antler-clashing behavior of bull moose in rutting season, said the study, which published by the academic journal Behavioral Ecology and Sociobiology.

"Because we have so much aggression in the big males, it actually masks female choice," said Dr. Terry Bowyer.

Female moose use protest moans to ward off small male suitors, the study points out. Researchers have now found that females moan more when they are approached by smaller males, and that this triggers aggression in larger males.

Bowyer and his study partners found they also use those protest moans when approached by some big suitors, setting off fights between large bull moose.

The biologists spent four autumns tracking and observing moose in Denali, listening to grunts and moans and recording behavior, including fights. They concluded that the females actually foment male-male aggression.

"It's indirect control," Bowyer said. "They're manipulating a mating system in which you think they didn't really have choice."

Bowyer suggested that the moaning behavior may serve a dual purpose. "This behavior by females helped them avoid harassment by smaller males, but also provoked fights between large males," he explained.

"Male aggression was more common when females gave protest moans than when they did not, indicating that this vocalization incited male-male aggression."

Dr Bowyer also suggested that female moose could purposefully provoke fights between males as a way of choosing their mates. "Female moose are courted continuously by all size of bulls in Alaska, and a master bull tries to keep other male moose out of his harem," Bowyer said. "This really limits female choice, but the females have two strategies."

First, the females can catch the attention of the master bull if a smaller, younger bull is trying to court her. The master bull chases those younger bulls away from his harem so the females are not bothered by them. However, female protest moans can also attract large dominate bulls from outside the harem to "foment big fights over the control of the harem," which also increases the choice of mates by female moose. Once the rut gets started big bulls round up harems of females, and sometimes other big bulls come in later and take control of the harem. Female protest moans can trigger clashes.

"Protest moans allow females to exert some choice in a mating system where males restrict [that] choice through male-male combat," he said.

Finding the right mate at the right time is critical for successful reproduction, the study points out, because of the "extremely synchronized manner" in which cows give birth in May and a restricted growing season, which limits young moose's opportunities to eat enough food to survive the harsh winters.

Source:
Reuters,"Alaska study finds female moose manipulate males to fight", accessed August 3, 2011
BBC Nature, "Female moaning spurs fights between male moose", accessed August 3, 2011
Idaho State University, "Female moose moans provoke bull fights; females have more choice in picking mates, concludes Idaho State University study", accessed August 4, 2011

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