Birds serenade their incubating eggs to control how their offspring will handle heat, Australian researchers have shown.
In a number of species, including fish and even humans, parents can guide the development of their offspring to prepare them for the environment into which they will be born.
Famously, children born in the Netherlands to mothers suffering from starvation during the Second World War have shown an increased tendency to become obesity and develop diabetes. This is reflected in subtle "epigenetic" changes in the offspring to genes that control metabolism.
Other studies have shown that the environment in which a fish is reared can affect the growth of the next generation.
Now researchers Mylene Mariette and Katherine Buchanan, from Deakin University, have shown that birds can also influence the behaviour of their young, but in a highly unusual way - by singing to them as they incubate inside their eggs.
Working with Australian zebra finches, Taeniopygia guttata, the Deakin duo showed that, in the final 5 days before hatching, parent birds sing a specific song to their eggs, but only when ambient temperatures are over 26 degrees Celsius.
To find out what role this might play in the chicks' development, eggs were incubated in artificial settings where they were played either control birdsongs, or the specific calls issued by parents when temperatures were high. Once the eggs hatched the nestlings where transferred to nesting boxes that were at a range of different temperatures.
Each day the nestlings were weighed. Those chicks that had been played the special bird song grew significantly less at higher ambient temperatures compared with the control chicks.
This effect was advantageous to them, however, because they also had more offspring compared with non-temperature-adapted birds kept at the same temperatures when they later came to breed.
The adapted birds also actively sought out nesting sites that were warmer compared with animals that had not been played the high-temperature bird songs during their incubation.
While the study, published this week in Science, does not dwell on the mechanism by which the change occurs, it does show that warm-blooded creatures like birds, despite the physical isolation of their chick inside an egg, can nonetheless influence the development and temperature tolerance of their offspring.
Critically, Mariette and Buchanan say, this gives initial insights into how animals like birds may cope in future in the face of global warming.