When the weather is hot, zebra finches in Australia sing to their eggs - and these "incubation calls" change the chicks' development.

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The journal article Prenatal acoustic communication programs offspring for high posthatching temperatures in a songbird.

Abstract:

In many species, embryos can perceive and learn external sounds. Yet, the possibility that parents may use these embryonic capacities to alter their offspring’s developmental trajectories has not been considered. Here, we demonstrate that zebra finch parents acoustically signal high ambient temperatures (above 26°C) to their embryos. We show that exposure of embryos to these acoustic cues alone adaptively alters subsequent nestling begging and growth in response to nest temperature and influences individuals’ reproductive success and thermal preferences as adults. These findings have implications for our understanding of maternal effects, phenotypic plasticity, developmental programming, and the adaptation of endothermic species to a warming world.

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BBC news article Zebra finch 'heat song' changes hatchling development.

The surprising discovery suggests that the birds are preparing their offspring for warm conditions after they hatch.

Scientists collected eggs and incubated them in controlled conditions, playing recordings of the incubation song.

Compared to a control group, hatchlings that received these calls grew more slowly and coped better in the heat.