As the sun rises over the Dead Sea, male rock hyraxes in Israel creep out of their darkened burrows and begin to sing.
To the human ear, the notes sound like a cross between a hyena’s cackle and chalk screeching against a blackboard. But to the female rock hyraxes, each chorus is a power ballad echoing out through the gorge—and the more the males maintain rhythm, the more likely the females are to swoon.
Combining spectrogram analysis of rock hyrax courtship songs
with the results of many successive breeding seasons, scientists have shown for the first time that males who sing more frequently and best maintain rhythm also go on to father better-surviving offspring, according to a study published this week in the Journal of Animal Ecology.
Colorful ear tags and collars allowed the scientists to identify the animals from a distance and match their songs to the results of paternity tests. (Listen to the males singing.)
“The most simple explanation is that being consistent in terms of rhythm is attractive, or at least reflects quality in some way,” says study leader Vlad Demartsev, a behavioral ecologist who was at the Max Planck Institute of Animal Behavior while the work was being conducted.
Like human tunes, rock hyrax songs tend to get more complex as they go on, building toward a climactic finish that seems designed to keep the listener on the edge of her seat—or rock ledge.
“It’s not just that they’re producing the signal. It’s not even that they’re producing the signal as many times as possible,” says Demartsev. (Read more about the novel noisemakers in nature.)
“It’s that they’re actually putting on a good show,” he says.
The song is mightier than the sword
Over the past two decades, scientists have been studying rock hyraxes, rabbit-size mammals whose closest relative is the elephant, in Israel’s Ein Gedi Natural Reserve.
When a male wins the right to live with a group of up to 30 females, juveniles, and pups, he may maintain that coveted position until the end of his days, at a ripe old age of nine.
However, in rare cases, a resident male can be overthrown and driven out of his station by a non-resident male, called a bachelor. This may be one reason why male hyraxes sing all year long, and not just mating season, which peaks for a few weeks in July and August.
Demartsev says it seems likely that signaling one’s value by way of singing may actually prevent aggression between males.
“It’s sort of a ritual that can minimize the need to fight, because that can be costly to both sides,” he says.
Bachelors vs. residents
In another fascinating finding, the scientists also detected a difference in the males’ singing styles.
While resident males produce frequent songs with steady rhythm, they actually decrease in complexity after they take over a group.
“All the females know you, and they know your qualities already. They live with you in the same sleeping burrows,” says Demartsev. “So you might need to invest less to get to the same point.”
But most males are bachelors, and their songs steadily increase in complexity as they age. (Read why this sparrow has suddenly begun singing a new tune.)
That may be because bachelors regularly try to woo away younger females on the periphery of the group. Yet these females also tend to be less experienced mothers, which may explain why offspring from the resident males are more likely to survive their first year of life.
As for why the females are drawn to males with rhythm, he adds, it’s still unclear. It might be that cramming so many notes into one breath reveals a level of fitness, and arranging them in a repeatable rhythm is the most efficient way to do that.
The ancient origins of rhythm
Just a few decades ago, many scientists assumed animals communicated in patterns that were more or less set in stone, says Chiara De Gregorio, a primatologist at the University of Turin in Italy and author of a 2021 study about singing lemurs that inspired the rock hyrax song research.
“Now we are learning that this kind of pattern can change depending on the context and even depend on other aspects, like male quality,” she says. (Read how singing mice can learn new tunes.)
Not only is this research important for better understanding rock hyraxes or lemurs, but each time scientists discover another species that communicates using principles like rhythm, it hints at the seemingly ancient origins of components that would eventually influence how humans create and enjoy music.
“At the end of the day, I think these patterns are very clearly more common [in the animal kingdom] than previously thought,” says De Gregorio.