Many of us pack our Spotify playlists with an eclectic mix of tunes to keep our party guests entertained.
Now, researchers have revealed that even birds like to mix things up with 30-minute-long playlists of their own to help attract a mate.
Biologists recorded the distinctive birdsong of male song sparrows (Melospiza melodia) in Pennsylvania to find patterns in their calls.
The males deliberately shuffled their song repertoire, they found, possibly as a way to keep it interesting for their female audience.
The study shows male song sparrows keep track of the order of their songs and how often each one is sung for up to 30 minutes, so they can change up their next 30 minutes of tunes.
Song sparrows are a common songbird throughout North America, but only males sing. They use their song to defend their turf and court mates
The new study was led by Stephen Nowicki at Duke University in North Carolina and William A. Searcy at the University of Miami, Florida. They claim song sparrows ‘communicate with the complexity of human language’.
‘Song sparrows cycle through their repertoires significantly more efficiently than would be expected from random sequencing,’ the team say in the paper, published in Proceedings of the Royal Society B.
‘Presumably also, many other general rules may be discoverable in some of the other 4,000 or so species of songbirds.’
Song sparrows are a common songbird throughout North America, but only males sing. They use their song to defend their turf and court mates.
When wooing, they sing up to 12 different two-second songs, a repertoire that can take nearly 30 minutes to get through, since they repeat the same song several times before going on to the next one.
In addition to varying the number of repeats, males also shuffle the order of their tunes each time they sing their back catalogue.
However, it wasn’t known whether males change up their song order and repeats by accident or by design.
To learn more, Searcy loaded up recording gear, trekked out to the backwoods of southwestern Crawford County in Pennsylvania, set up mics pointed to the trees and patiently waited for five hours a day.
‘Adult male song sparrows were recorded on their territories in old fields and forest clearings and along the shores of lakes and waterways,’ Searcy and colleagues explain in the paper.
‘Each subject was recorded on two mornings with a mean of 9.5 days between recording sessions.’
Spectrograms of eight song types in the repertoire of a male song sparrow. Spectrograms visually represent the signal strength, or ‘loudness’, of a signal over time at various frequencies present in a particular waveform
After recording the full suite of songs from more than 30 birds, the team pored over visual spectrographs of the audio and analysed how often each song was sung and in what order.
Much like a Spotify playlist, the male birds generally sang through their full repertoire before repeating a song, they found.
The researchers also found that the more a sparrow sang a given song, the longer he took to get back to that song, possibly to build up hype and novelty before that song was sung again.
For example, if a male sang ‘Song A’ 10 times in a row, he’d sing even more renditions of his other songs before returning to Song A again.
Alternatively, if Song A was only warbled three times during a set, then a male song sparrow tended to recite a shorter rendition of the rest of his repertoire in order to return to Song A.
Taken together, these findings demonstrate that song sparrows possess an extremely rare talent known as ‘long-distance dependencies’, where one element affects choice of another occurring considerably later.
In other words, it means that what a male song sparrow sings in the moment depends on what he sang as much as 30 minutes ago.
Pictured, a song sparrow (Melospiza melodia) calling while perched on a tree stump in Pennsylvania, US
At 30 minutes, male song sparrows have a 360 times larger memory capacity than the previous record holder, the canary, which can only juggle about five seconds worth of song information in this way.
It remains to be seen whether better shuffling ability gives males an advantage at finding love, however.
It’s possible females maintain interest in a mate who mixes it up more, and are less likely to go off with another male.
Future research could test this by comparing birdsong data with paternity tests of chicks laid by a female song sparrow, according to the team.