Several types of birds sing to unhatched eggs so their young will recognize their voices once they've hatched—but what the zebra finch does is something else entirely. In a study called "paradigm-shifting" by one of its authors, researchers at Australia's Deakin University say the birds sing a song to their eggs that keeps chicks from growing too big—but only when the weather is warm, with scientists suspecting that smaller birds are able to get rid of excess body heat more easily. Think of it as "an early weather advisory," per Smithsonian. After placing microphones in 125 zebra finch nests in an outdoor aviary, researchers heard finches singing a specific song in a certain scenario: when they were alone with eggs, the eggs were days away from hatching, and the temperature was above 78 degrees, reports New Scientist.
The researchers then incubated 170 finch eggs in a lab, playing a recording of the song to only half before putting them back in nests. The chicks that heard the song and grew up in warmer nests weighed less than chicks in cooler nests, produced up to six fledglings in their first breeding season (compared to one or two), and chose warmer nests in later life. "Hearing that call before you even hatch affects your development, affects your growth rate," says the university's Kate Buchanan. Adds author Mylene Mariette, the "strategy ... could potentially help them deal with global warming." (Here's what happened when scientists got the birds drunk.)