Female moose may be able to manipulate amorous males - inciting fights between male competitors by moaning. It was already known that females made "protest moans" in response to courtship. Researchers have now found that females moan more when they are approached by smaller males, and that this triggers aggression in larger males. The scientists believe that females have more control over mate choice than previously thought. A team led by Dr Terry Bowyer from Idaho State University in the US carried out the study in Denali National Park and Preserve, Alaska. Their findings are published in the journal Behavioural Ecology and Sociobiology.The species Alces alces is referred to as elk across Europe, but is known as moose in the US. The animals are polygynous, which means that one male mates with multiple females but each female only has one male partner. Reproduction takes place during the autumn rut, when males compete for females. This often results in fierce battles. Previous research has shown that, during courtship, female moose moan in protest when they are approached by males. By observing the moose during the mating season, the scientists discovered another level of complexity to the females' communication. "Female moose gave protest moans more often in response to courtship by small males, even though the large males engaged in more courtship," said Dr Bowyer. The moose expert, who has studied the animals in this region since the mid 1980s, realised that the females' moans had a dual purpose. "This behaviour 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 vocalisation incited male-male aggression." Dr Bowyer also suggested that female moose could purposefully provoke fights between males as a way of choosing their mates. "Protest moans allow females to exert some choice in a mating system where males restrict [that] choice through male-male combat," he told the BBC. Female choice, he concluded, may have been undervalued, because it was "masked" by male-male combat. Dr Bowyer said: "We believe that female choice is a more critical component of mating systems in polygynous mammals than previously thought."