科学美国人60秒:Wild Songbirds Can Pick Up New Tunes

Only a few kinds of animals are known to learn their vocalizations from listening to others. Us, of course. Elephants. Bats. Cetaceans—whales and dolphins. Pinnipeds—walruses, seals and sea lions. And parrots, hummingbirds and songbirds. That's it. 

"When your cat meows or your dog barks, it does that because it has genetically inherited that sound. But birds are like us, young animals have to hear adults in order to develop normal sounds."

University of Windsor biologist Daniel Mennill. 

There have been hundreds of conventional experiments done in laboratories with captive birds that support the idea that young birds learn to sing by listening to older birds. These studies also taught us that birds, like humans, have what's called a "sensitive period" early in life, a time when they are most disposed to learn how to vocalize from their elders.

But nobody ever did one of those experiments with wild birds. Observational studies, yes. But no true experiments. Until now, thanks to some wild savanna sparrows.

"So this population of savanna sparrows lives on an island in the Bay of Fundy in eastern North America, and it's been studied since the 1960s, so we know a lot about this population. It means we know every kind of sound that has ever been uttered by a savanna sparrow in this population over the course of many decades."

Mennill and his team installed a series of loudspeakers on the island, and they played new tunes that the sparrows would never have heard otherwise. 

"The kinds of sounds that we broadcast to the animals were based on savanna sparrows, the same species, but recordings collected on the western coast of North America, many thousands of miles away from our study population."

For six years, the researchers broadcast these novel songs to five cohorts of sparrows. 

 "Lo and behold, this bird that arrived to breed in the spring of 2014 opened his beak and sang a song that was a perfect match with one of our stimuli." 

In all, 26 birds learned their songs from loudspeakers rather than from other birds. And they had the same survival and reproductive success as all the other birds. All but one successfully mated and defended their territories. And four additional birds learned songs from birds that had originally learned from the loudspeakers.

"What we have now is a very unique, maybe a globally unique population of animals, where some of the animals sing population typical songs, that sound like other animals in their breeding population. But our experimental subjects who are living there now, are singing songs that are slightly different." 

By returning to the island year after year, Mennill can study not only vocal learning, but the transmission of culture from one generation to the next. There’s a lot going on in those bird brains. 

—Jason G. Goldman 

[Daniel J. Mennill et al., Wild birds learn songs from experimental vocal tutors]