For Male Fallow Deer, Mating Calls Are A Sign Of Strength And Competition

By Ajit Jha on February 9, 2014 7:03 PM EST

fallow deer
Although mating calls among male fallow deer are meant to attract females, they also indicate to other bucks one's strength and ability to compete. (Photo: Kitty Terwolbeck, CC BY 2.0)

Mating behavior among mammals is an intensely researched subject, and there are still things we haven't learned. A recent study published in the journal Behavioral Ecology reveals that fallow bucks rely on the sound quality of rival males' mating calls to decide whether they should fight the buck or stay away - the calls indicate a buck's physical strength.

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Previous studies have found that male fallow deer, known as bucks, can express over 3,000 mating calls in an hour during the peak of mating season. During the season, called a rut, they eventually become exhausted from long hours of calling, fighting, and mating, and begin to sound hoarse. In fact, Dr. Benjamin Pitcher from Queen Mary's School of Biological and Chemical Sciences counts fallow bucks among "the most impressive vocal athletes of all deer," according to a press release.

"Until recently we have known relatively little about who is listening to their calling, and what information they are hearing," said Dr. Alan McElligott, who is also from the Queen Mary School of Biological and Chemical Sciences, in the press release. The calls or groans the bucks make not only attracts females but also deter competitors. Their calls contain a large amount of information indecipherable to the human ear, including their status within the herd and their size. The scientists discovered this after a set of experiments exploring how the rivals responded to changes in calls, different frequencies, and vocal fatigue.

The scientists conducted their study at Petworth Park in West Sussex, England during the peak of their rut. The scientists played recorded groans that were slow and fast, as well as calls from early and late - as if the deer were tired - in the mating season. The scientists then observed the amount of time the deer took to respond to the calls, along with their posture, orientation, and responding calls.  

The researchers found that the deer were more likely to respond to faster calls than slower ones, signifying a greater degree of motivation or aggressiveness. Groans from earlier in the rut were more likely to be threatening as well, obviously because the bucks didn't sound as fatigued. "We know from this recent study that by detecting changes in calls, bucks are able to judge which rival is most vulnerable to be challenged and when to fight," Pitcher said in the release.

Vocal fatigue is a tell-tale sign that a buck is worn out from the strains of mating. It is well-known that, during the mating season, male deer stop feeding and lose over a quarter of their body weight due to stress from looking for a mate.

"The findings demonstrate how sexual selection has shaped the vocal behavior and communication system of fallow deer," McElligott said in the release. "We see this trend with other mammals that have similar vocal systems, such as seas lions. The study helps to develop an understanding of how competing for, and attracting mates, has influenced the evolution of communication systems, including human speech."

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