August 8, 2011 — Vol. 27 No. 31
Idaho State University biological sciences Professor Terry Bowyer and colleagues have documented that vocalizations by female moose can incite aggression among males. The study, recently featured on the BBC, suggests that female moose may have more choice in picking mates than previously thought because their protest moans can create problems for potential mates, Bowyer said.
"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."
Non-dominant bulls hang out on the periphery of the harem, according to Bowyer, and these "satellite males" attempt to sneak copulations from females.
"The females moan a lot more if a small bull comes in and it attracts the dominant bull to chase the smaller bulls off, reducing the harassment from young males," Bowyer said.
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.
"Occasionally a female will moan during courtship by a dominant male and if another big bull is around it can provoke a fight," Bowyer said.
The bottom line, according to Bowyer: "There was much more male aggression in our sample areas where we recorded female protest moans."
And, although it isn't in the paper "Vocalization by Alaskan moose: female incitation of male aggression" published in the Behavioral Ecology and Sociobiology, the study also suggests hunters after big bulls should use female moose moaning calls.
"If a hunter is after a really big bull they should use moaning calls instead of an antler rattle or antler thrash," Bowyer said. "Antler rattling is not as effective as calling in big bulls as using a moan call."
Bowyer's co-authors on the study were Janet Rachlow, Department of Fish and Wildlife Resources, University of Idaho; Kelly Stewart, Natural Resources and Environmental Sciences, University of Nevada Reno; and Victor Van Ballenberghe, Department of Biology and Wildlife, University of Alaska Fairbanks.