for National Geographic News
Those who live near nightingale nests know all too well that the males often sing all night.
Yet the birds aren't considered nocturnal animals, as they feed, socialize, and do most of their singing during daylight hours.
"We were really curious why it was that some nightingales were singing in the middle of the night," said Valentin Amrhein of the University of Basel in Switzerland, lead author of a new study on the birds.
His team noticed that once a male nightingale joined up with a female, he stopped his nightly serenades but continued his daytime singing.
Further analysis revealed that single males remained stationary at night but moved around—sometimes to the edge of other males' territories—while singing during the day. This suggested that daytime tunes are for exploring territorial barriers, while night singing is for something else.
A final experiment with female nightingales solved the puzzle. The researchers found that while unpaired males sit still and sing all night, females become extremely active around midnight.
The females flew from male to male, listening for a few minutes to the unpaired singers. This leaves little doubt that the females are effectively "shopping around" at night for the best partner, Amrhein said.
"What is perhaps the most exciting find here is that we have found a species where females search for mates at a different time of the day than males search for territories," he said.
"We've never seen that before [in any animal]."
Findings published in the journal Proceedings of the Royal Society B.
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