Know how male deer decide whether to fight with rival deer or leave them exhausted and rush after that call for mating? Scientists know now.
A male fallow deer, known as bucks, can call for a mate more than 3,000 times per hour during the peak of the mating season.
Rest of the deer listen to the sound quality of rival males' calls and evaluate how exhausted the caller is and whether they should fight or keep their distance, shows new research.
"Fallow bucks are among the most impressive vocal athletes of all deer and invest a large amount of time and energy in calling," explained Benjamin Pitcher from Queen Mary's School of Biological and Chemical Sciences in Britain.
During the mating season, fallow bucks produce a call or groan, both to attract mates, and repel competing males.
Groans contain numerous clues about each animal, such as their size and status in the herd.
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The researchers set up a series of playback experiments to investigate how the bucks responded to changes in calling rates and vocal fatigue in the groans of their rivals.
"Until recently, we have known relatively little about who is listening to their calling, and what information they are hearing," said Alan McElligott, also from Queen Mary's School of Biological and Chemical Sciences.
The scientists played slow and fast rate groaning sounds, as well as groans from early in the mating season and ones from late in the mating season to mature male deer in Petworth Park, West Sussex.
The speakers were hidden from view and scientists measured how long it took for the deer to react to the calls, as well as their orientation, posture, and calls they made in response.
The deer were more responsive to fast rate groans than to slow rate groans indicating that bucks signal their motivation or aggressiveness in how quickly they call.
This shows that bucks can detect when rivals are becoming fatigued and that exhausted males pose less of a threat.
"We know that by detecting changes in calls, bucks are able to judge which rival is most vulnerable to be challenged and when to fight," added McElligott.
These results help us to understand how vocalisations and behaviours associated with mating have evolved, said the study published in the journal Behavioral Ecology.