Scientists have discovered something unexpected about the way birds communicate with their unborn chicks.

One species sings a special song to their eggs to warn their offspring if the weather outside is getting too hot.

On hearing the song, baby zebra finches hatch sooner and gain less weight - meaning they're smaller and better able to keep themselves cool.

Ducks and chickens also 'speak' to their eggs, meaning that when they hatch they already recognise their parents by their voices.

They are well-developed when they are born, but scientists did not realise that birds which hatch at an early stage - like zebra finches - could also hear through their shells.


Mylene Mariette from Australia's Deakin University said: "We didn't realise that they were able to hear before hatching."

Scientists spotted the behaviour among captive zebra finches in Australia - while they often call to one another, they noticed that sometimes the birds sang a specific song when alone with their eggs.

This occurred when the weather was warmer, and it was found that it caused the birds to hatch sooner.

The benefit of this appears to be the fact that it's easier for smaller birds to cool themselves in the hot weather.

Sonia Kleindorfer at Flinders University in Adelaide told the New Scientist magazine: "This is a remarkable study.

"Zebra finches are literally right in front of us in cages around the world. What are we ignoring that is right before us?"

It is unclear whether wild zebra finches also exhibit the same behaviour as captive ones.