Birds have a rich vocal repertoire that they use to communicate with their peers, but behavioural ecologist Mylene Mariette is more interested in the calls they make when they are seemingly alone.
While working as a researcher at Deakin University, in Victoria, Mariette planted microphones in the nests of captive zebra finches (Taeniopygia guttata) to study how male-female pairs coordinate their parenting efforts. One day in 2014, she noticed that “sometimes one parent would produce a very different call when it was incubating by itself”, Mariette recalls, which led her to wonder “whether it was communicating with the embryos, because they were the only audience there.”
The cry she overheard – a form of vocal panting – is one that finches produce when temperatures rise, and while further observations showed that they do sometimes produce this heat call when alone or around other adults, it is most often made in the presence of eggs, especially those nearly ready to hatch. And the developing chicks respond: playback experiments revealed that chicks that heard the call before hatching grew more slowly, possibly to reduce the oxidative stress caused by high temperatures or to maximise heat dissipation from their
