Rhythm of love
Male hyraxes that sing in the strictest tempo get females’ pulses racing
Mammals bellow, roar, squeal, snort and bark, but few could be said to sing. With a handful of notable exceptions – gibbons, indri lemurs, whales and hyraxes – singing is for the birds. New research shows that, in the case of singing male hyraxes, they have rhythm, too. And the more rhythmically precise their song, the more offspring they produce.
Rock hyraxes, also known as rock rabbits or dassies, are no nightingales. The vocalisations they broadcast during the mating season – a harsh combination of grunts, barks and squeaks – are classed as songs due to their complexity.
“The song is pretty unique for a mammal,” says Vlad Demartsev, lead author of the new study published in the Journal of Animal Ecology. “It’s very long and is structured into bouts. They make a sequence of sounds and then pause for a second and start again – pause, start, pause, start and so on for five or six minutes.”
Working on hyraxes in the deserts of eastern Israel, Demartsev and his colleagues analysed the time intervals between neighbouring notes within each bout. “They are almost identical – very precise,” he says. “If they start slow, they remain slow for the rest of the bout. And if they start fast, they stay fast, until finally they reach a complex and climactic ending.”
And the degree of rhythmic consistency seems to indicate a male’s attractiveness to females, as the males that kept tempo most precisely went on to father the most offspring. “Rhythmic display could be a reflection of a male’s quality because it requires precise muscle control and coordination,” says Demartsev, who is based at Germany’s University of Konstanz. The findings may also have implications for the origins of human music. One theory goes that rhythmic components of songs evolve to allow synchronisation between individuals who sing together in chorus – in the duets of gibbons, for instance. But the hyrax work suggests that it can also arise in solo performers advertising their quality to potential mates.