As hunters know, calling plays an important role in a buck’s life come the rut. A new study published today in the journal Behavioral Ecology suggests that deer have a complicated response to the groans made by rival males, and that the strength of the call may make a difference in whether the buck approaches the source or leaves.
“Until recently we have known relatively little about who is listening to their calling, and what information they are hearing,” Dr. Alan McElligott said in a press release.
The study was conducted by researchers from Queen Mary’s School of Biological and Chemical Sciences in the University of London. Scientists carried out the experiments by playing different calls from various periods of the rut to fallow deer bucks in West Sussex with the use of hidden speakers. The researchers then recorded the reactions from the males, including how long it took the animals to react, their posture, and the calls made in response.
Male fallow deer are capable of calling more than 3,000 times per hour during the height of mating season, not unlike deer elsewhere in the world. As the rut runs on, bucks will become increasingly tired due to the lack of food, fighting with rivals, and if they are fortunate, the actual act of mating. The purpose of these calls are to draw in prospective females and to warn other males. The study suggest that deer can instinctively measure physical prowess through the rate and strength of these calls.
“Fallow bucks are among the most impressive vocal athletes of all deer and invest a large amount of time and energy in calling,” explained Dr. Benjamin Pitcher, another researcher on the study.
The scientists found that deer were more responsive to fast rates of groans and calls from early in the rut, as opposed to the exhausted groans from a buck late in the mating season. Male fallow deer will modulate their calling rates if there are other deer nearby, regardless of gender. According to the study, these calls signal motivation or aggressiveness. Playbacks of these fast rate groans saw bucks becoming attentive both sooner and for a longer span of time. The same was true for early rut calls.
“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.
The experiment revealed that bucks are less threatened and more relaxed within earshot of a tired male as opposed to one that is very energetic. Researchers speculate the strength of these calls play a large role in how male deer behave during the rut, including which rivals to challenge and which ones to avoid.
“These results help us to understand how vocalisations and behaviours associated with mating have evolved,” said McElligott. “The findings demonstrate how sexual selection has shaped the vocal behaviour and communication system of fallow deer. We see this trend with other mammals that have similar vocal systems, such as sea 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.”