How do male chimps ask for sex? It depends on their local dialect

CBC

14-02-2025

When a male chimpanzee wants to hit on a female without causing a scene, he sometimes has to get a little creative.
"The alpha male, he can mate with whoever he wants, whenever he wants, and he gets at least half of the offspring," Catherine Crockford of the Max Planck Institute for Evolutionary Anthropology told As It Happens host Nil Köksal.
"The subordinate males, they want to have their go. But, you know, they can't if the alpha male spots them."
To avoid the alpha's wrath, Crockford says males use covert physical gestures — which she calls "the sneakies" — to solicit sex. These mating moves, which she and her colleagues documented for a new study, vary between chimpanzee communities, suggesting chimp populations have their own distinct dialects.
Crockford says the findings, published in the journal Current Biology, show that chimpanzee conservation is about more than protecting animals; it's about safeguarding entire cultures.
Northern knuckle-knockers
Crockford and her colleagues looked at the use of mating signals over the course of 45 years among chimpanzees at the Taï National Park in Ivory Coast.
Four groups of chimps call the park home, identified by which area of the park they inhabit: north, south, east and northeast.
The researchers observed four distinct ways males signalled a desire for sex: knocking their knuckles on a hard surface, kicking their heels, tearing strips from a leaf and waving a branch.
While all four groups perform the branch and heel gestures, only the chimps in the northeastern part of the park knuckle-knock and only the southeastern chimps use the leaves.
It's a surprising difference for two populations who have a shared gene pool and live just 500 kilometres apart in the same habitat, Crawford said.
"The only way that this can come about is that the young males must learn from watching the older males," she said.
Julie Teichroeb, who studies primate behaviour at the University of Toronto Scarborough, says she's not surprised by the findings.
After all, she says, differences in vocal communications have been well-documented in many different types of animals.
Different populations of whales and songbirds, for example, are known to have unique regional dialects. Recent research suggests elephants may even have their own distinct names for each other.
Chimpanzees, too, have been shown to have geographic differences in their "pant hoots" which are loud, long-distance calls. In that case, Teichroeb notes, it's unclear whether the differences are cultural or genetic.
Culture is fragile
In the case of the Taï National Park study, Crockford says there's clearly a cultural factor at play. And cultures, she says, can be lost.
In fact, the scientists have already seen this play out.
One of Crockford's colleagues, field assistant Honora Néné Kpazahi, first noticed decades ago that males in the park's northern population were knocking their knuckles to get females' attention.
But over time, the gesture's prevalence declined as several disease outbreaks, some spilled over from humans, ravaged the population until only two males were left.
Illegal poachers killed one of those males, Marius, in 2004. With only one male left standing, the gesture was no longer needed, and it's been lost to that group ever since. Now, only the northeastern chimpanzees do it.
The same thing, she says, can happen to other learned behaviours, like the use of tools, which also varies between populations.
"The sad thing is that we now know that not only does [poaching] kill chimpanzees, but it kills the cultures," she said. "These cultures can take generations to emerge, we think. And, you know, if you lose those skills, then it might actually impact your survival."
Teichroeb said in an email the loss of that knuckle-knocking gesture among Ivory Coast chimps shows "how fragile animal culture is, just like human culture."