Few animal courtships are as strange or, quite frankly, as silly as that of the greater sage-grouse (Centrocercus urophasianus). In early spring, sage grouse bachelors – resplendent in their spiky fantail finery – gather in large numbers on the North American sagebrush plains to compete for a mate. Known as leks, these events are essentially sage grouse discos; the battle for sex is played out using the medium of dance, with the males strutting about, providing their own unlikely soundtrack by, basically, beatboxing.
Female choice is the most whimsical of evolutionary powers, with a hand in some of nature’s most extravagant creations: the male peacock’s tail; the stalk-eyed fly’s outlandish eye stalks; and the greater sage-grouse’s absurd beatboxing routine
Male greater sage-grouse have a massively distended oesophagus that they can inflate by gulping down mouthfuls of air to create a large, wobbly, white-feathered throat balloon, which when fully swollen briefly exposes two bulbous patches of olive-green skin that pop forth like a pair of shop-dummy breasts. It’s a pretty eye-catching look and, by controlling the expulsion of air, the cocks are able to slap their olive sacs together to generate an even more arresting noise: a loud, high-pitched doink that sounds as if it were made by twanging rubber bands over water.
The overall effect is pure Monty Python and begs the question, “Evolution, what were you thinking?” What perverse force could have shaped such preposterousness? The answer: female choice.
Female choice is the most whimsical of evolutionary powers, with a hand in some of nature’s most extravagant creations: the male peacock’s tail; the stalk-eyed fly’s outlandish eye stalks; and the greater sage-grouse’s absurd beatboxing routine.
Trying to fathom what females are choosing has long fascinated Gail L Patricelli, one of the leaders in this field. She’s infiltrated the greater sage-grouse courtship routine by creating a robot female on wheels, which she can drive into the lek.
The female greater sage-grouse is a smaller brown bird and boasts none of the male’s fancy finery. When casually observed at the lek, she appears to confirm all the classic stereotypes of female passivity. While males are beatboxing like fury, she pecks away at the ground, apparently uninterested in the show. It seems as if the males are competing, and the winner gets the mating rights with these passive hens.
But Patricelli’s fembot has revealed a more nuanced negotiation between the flamboyant males and the females. Although they may seem passive, the females are in fact listening and watching the male’s every move. They prefer the most energetic males, suggesting that these individuals have the best genes. But more than that, Patricelli has discovered that the females are giving off subtle cues themselves. If the male doesn’t heed to these cues, no matter how energetic his display, she will refuse to mate.
So, the secret to being a winning male isn’t just about being the top cock, it involves listening as well.
Main image: illustration by Holly Exley