Birds sing to prepare chicks for the heat

A native Australian songbird prepares its unhatched chicks for warm weather by singing to them when it gets hot, according to a study published in Science.

A pair of biologists from Deakin University in Australia found the zebra finch’s song – dubbed “incubation calling” – changes the physical development of the chick embryos so they end up smaller in a warmer environment.  

Despite a lower body mass typically being a disadvantage for birds in the wild, being smaller means the chicks may scale back the build-up of unstable molecules called reactive oxygen species which can damage cells and DNA.

And, the study found, the smaller finches produced more birds able to fly, or fledglings, in their first breeding season than those who weren’t exposed to the incubation calls. 

“Finding that birds talk to their eggs and that it has such a profound effect on their embryos, and even two years later we can still see effects, I think in the broader picture it’s the most amazing thing,” says lead author Mylene Mariette.

Since zebra finches breed any time during the year (so long as the conditions are right, such as having enough to eat) incubation calling gives them a way to survive climate change as a species.

The finches start incubation calling when their eggs are only five days from hatching, and only when the temperature hits 26°C or higher.

This short timeframe is when the embryos grow to fill most of the egg and can hear outside sounds through the shell, including calls from their parents.

Mariette and her colleagues Katherine Buchanan tested how incubation calling affected a hatchling’s size by playing the recorded calls to some eggs while others heard normal parent sounds. And sure enough, when the chicks hatched, those exposed to incubation calling were smaller.

So how can something as simple as sound change the chicks’ development?

Mariette isn’t sure yet. But she speculates that it has something to do with how the auditory centres in the brain are connected to the hypothalamus – a region of the brain that regulates the body’s metabolic processes, including body temperature, thirst and hunger.

Previous studies on inland fish species and flies showed parents could influence the development of their unborn offspring, but this is the first time a warm-blooded animal has been seen to do the same.

“We need to know if it happens in other species and if it could really make a difference to how other species adapt to climate change,” she says.