Desert birds prepare their babies for the heat

Deakin University researchers have discovered that the zebra finch, a small Australian desert bird, calls to its embryos during incubation to warn them about the heat they will face upon hatching. The study authors claim that this previously unknown function will not only prove critical for thriving in a warming climate, but also shows how much impact the prenatal acoustic environment has on development.

Writing in the journal Science, researchers Dr Mylene Mariette and Professor Kate Buchanan said embryos’ capacity to hear and even learn external sounds has been known since the 1960s, in humans and animals alike. “Yet,” they said, “the possibility that parents may use these embryonic capacities to alter their offspring’s developmental trajectories has not been considered.”

The scientists conducted a study in which they placed small microphones in nests of incubating zebra finches, breeding in outdoor aviaries at Deakin. In over 600 hours of audio recording, parents only called to their eggs when ambient temperatures rose above 26°C.

“Moreover, parents did not call to freshly laid eggs,” said Dr Mariette. “Calling only occurred within five days of hatching, once embryos had presumably developed hearing capacities.

“This suggests that parents are deliberately communicating with their embryos about the heat.”

By exposing the eggs to acoustic playbacks in artificial incubators, the researchers confirmed that the embryos were paying attention to their parents’ calls. “Nestlings hatched from eggs exposed to this heat-warning call reacted differently to temperature after hatching, compared to control nestlings that heard another type of parental call,” Dr Mariette said.

“Prenatal acoustic exposure changed both how nestlings solicited food to their parents and how much weight they gained throughout their development, in relation to temperature.”

The effect was not only short term, either, with Dr Mariette stating, “Astonishingly, the calls birds heard as embryos impacted on these individuals until adulthood, up to two years later.

“We found that adjusting their growth rate to ambient temperature allowed experimental birds to themselves produce more young as adults,” she said. Acoustic experience also changed bird thermal preferences at adulthood, with the birds exposed as embryos to parental incubation calls preferring to breed in hotter nests than control birds.

Dr Mariette said the study “highlights that acoustic environment may have a much stronger impact on development than we currently realise”, as “such profound and long-lasting effects of prenatal acoustic experience [had] never been demonstrated before”.

“This is also the first evidence that parents can adjust the development of their offspring to ambient temperature in warm-blooded species,” she said.

The researchers’ next priority is to establish the physiological mechanisms underlying these effects and how widespread this strategy is in birds.

Zebra finch image courtesy of Nicholls of the Yard under CC BY-NC 2.0