Humans love to take liberties when we talk about our heights. But Afruca tangeri fiddler crabs don’t have that luxury. Looking and listening in on the members of this species as they tried to attract mates, a team of researchers found that the males’ mating songs are shaped by their size, and are thus accurate signals of their fitness as mates, according to a press release, at least from the perspective of female fiddler crabs.

Publishing their findings in a study in the Journal of Experimental Biology, the researchers say that their results reveal what information male fiddler crabs share in their songs, as well as how well they share it.

Read More: How Do Whales Hear Their Songs and Other Sounds If They Don’t Have Ears?

Conveying Size Through Song

Scuttling around the noisy seashores of the Southern Iberian Peninsula, A. tangeri males court A. tangeri females through songs of seismic vibrations, by drumming or hitting the sand with their oversized claws or shells. But little is known about what, exactly, these seismic vibrations convey and how effectively they convey it next to the noisy sea.

Setting out to learn more, a team of researchers from the University of Oxford’s Animal Vibration Lab recorded male fiddler crabs as they produced their seismic signals. Using GoPro cameras and geophones, which measured the percussive vibrations that the crabs produced in the sand, the team revealed that the seismic signals differed depending on whether the males drummed the sand with their claws or hit the sand with their shells.

Much more intriguingly, the researchers also found that the seismic songs differed depending on the males’ morphology, allowing the females to accurately size up the males from far away.

“It appears as though the males cannot, or do not, lie about their physical size,” said Tom Mulder, a study author and a biologist at the Animal Vibration Lab, according to the release. “Females can rely on the loudness of seismic signals to honestly assess a potential mate’s quality, all without needing to see him.”

Read More: Understanding How Whales Communicate

The Complicated Steps of Fiddler Crab Courtship

Throughout their study, the researchers’ GoPros and geophones allowed them to record the complicated steps of fiddler crab courtship. First, the males waved their oversized claws in the air. Second, they alternated between drumming the sand and hitting the sand with their claws and shells. Third, they performed both behaviors simultaneously. And fourth, they scrambled into their burrows and drummed the sand there, if and only if a female seemed interested.

Recording vibrations for over 8,000 of these fiddler flirtations in total, the researchers found that the length, the loudness, and the rhythm of the crabs’ seismic signals differed depending on the crabs’ behavior — whether the crabs were drumming with their claws or hitting with their shells, for instance — allowing their behaviors to be differentiated based on their vibrations alone.

Also shaping the males’ songs were their morphologies, with larger and smaller claws producing higher-energy and lower-energy seismic signals, respectively.

“Larger claws have the advantage of overcoming seismic noise so that they can signal to females that are further away,” said Beth Mortimer, another study author and a biologist at the Animal Vibration Lab, according to the release. “However, the advantages are only observed for the percussive signals such as drumming and fortunately for smaller clawed crabs, these are only part of the courtship routine.”

According to the team, the percussive signals of these crabs are advantageous for males, allowing them to attract females next to the sounds of the sea. But they’re also beneficial for females, too, making sure that the males they meet actually measure up.

Read More: Yes, Fish Can Communicate Acoustically

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Sam Walters is a journalist covering archaeology, paleontology, ecology, and evolution for Discover, along with an assortment of other topics. Before joining the Discover team as an assistant editor in 2022, Sam studied journalism at Northwestern University in Evanston, Illinois.