Zebra finches are adept vocalists; mates often call to one another as they share parental care. But Mariette noticed that, sometimes, just a few days before their offspring hatched, the birds would sing when they...

“That’s a strategy we really didn’t know birds could do, and that could potentially help them deal with global warming,” study coauthor Mylene Mariette of Deakin told New Scientist .

PIXABAY, JPROHASZKA Zebra finch parents seem keenly aware of the weather during the last few days of incubating their eggs. And if it’s warmer than usual, they let their unborn chicks know. In a study published last week (August 19) in Science , researchers from Deakin University in Victoria, Australia, have shown that the birds croon a special song that seems to trigger changes in their chicks’ development. The chicks grow more slowly and, as adults, have more offspring of their own, the researchers showed.

To examine the effects of this call, Mariette and her colleague Katherine Buchanan, also at Deakin, experimentally controlled the sounds that dozens of eggs heard, New Scientist reported. For three to five days before the eggs hatched, the scientists incubated them in warm conditions—around 100 °F—and played them socialization songs. For one group of unborn chicks, they also played the “heat call.”

Chicks primed with their parents’ hot-weather warnings grew more slowly and weighed less as they matured than did those that hadn’t heard the special song, Mariette and Buchanan found.

And the slower-developing offspring were more fit. The females that were primed for warmer weather had up to six fledglings in their first breeding season, whereas those that were not tended to have only one or two, New Scientist reported.

The fitness advantage may stem in part from the benefit of having a smaller size for more effective heat loss in a warmer climate, the authors wrote.

Whether developing avian embryos are directly affected by a song remains a mystery. “They’re not actually thinking, ‘Mum says it’s hot out there, I better take it slow when I get outside!’” Nicola Hemmings, who studies bird reproduction at Sheffield University in the U.K. and was not involved in the work, told the BBC. “But [this song is] having some kind of physiological effect on their body which is making their growth rate slow.”