For a study published today in Science, they put a bunch of zebra finch eggs in an incubator that created a temperature around 100 degrees Fahrenheit.
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That song appears to keep the chicks from growing too large after they hatch if the weather is toasty – and it even affects the number of baby birds in the next generation, though researchers aren’t sure exactly why. The researchers realised that chicks might be listening from inside their eggs when they noticed that their parents, which normally call to one another, sometimes sang a specific song when they were alone with the eggs.
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.
Male and female zebra finches warn offspring still in eggs about warmer temperatures.
To find out whether the calls somehow prepared the chicks for higher temperatures, the scientists artificially incubated 166 eggs at a standard temperature of 37.7°C (99.9°F). The researchers found that nestlings that had been exposed to the calls as embryos ended up weighing less than control nestlings. “We didn’t realise that they were able to hear before hatching”, Mariette says. Though a smaller mass would seem disadvantageous, the authors showed that it actually correlated with less oxidative damage – the harmful build-up of unstable molecules in DNA, proteins, and fats – thus arguing that reduced mass may ultimately benefit finch health at stressful higher temperatures. Bird parents can influence their offspring in other ways, for example by changing the mix of hormones and nutrients that goes into the egg. And the incubation calls may have other lasting effects.
“It’s interesting and surprising that vocal communication at such an early stage of development could have such persistent effects”, says Renee Duckworth, an evolutionary ecologist at the University of Arizona in Tucson. This suggests the calls are a way to tell the soon-to-be-born finches about the world outside, and not just the parents complaining about the heat.
Incubation calls were first found in superb fairy wrens (Malurus cyaneus), another Australian songbird in a different family.
“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.
Mariette and Buchanan returned about 170 hatchlings to nests scattered around the aviary, some of which were sunnier and so warmer than others.
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Those babies also grew up to have more babies of their own. She also wonders how often finches use the incubation calls in the wild, because fairy wrens suffer increased predation when they make these sounds.
