Heat is on for bird calls
RECENT research has cast new light on the reasons why zebra finches issue a unique “hot call: when temperatures rise.
Hearing this call (produced by adult zebra finches when the temperature rises above 26ºC in the nest) while still in the egg changes the development of nestlings and their subsequent reproductive success at adulthood, according to previous studies by researchers from Deakin University’s Centre for Integrative Ecology (CIE).
While the researchers originally thought parent finches used the call to communicate with their unhatched babies, their new study has found parents don’t produce this hot call solely for their embryos.
“What we discovered is that they produce it whenever they are feeling too hot, even with no eggs present,” said lead researcher ARC DECRA Fellow Dr Mylene Mariette.
“Heavier adults that typically struggle more in the heat call more than leaner individuals. So it turns out that rather than parents calling especially to inform their embryos, they most likely call for other reasons, including perhaps to keep cool. Embryos then spy on their parents’ hot calls, to know when their parents are struggling with the heat.”
The researchers’ audio recorded wild zebra finches in breeding and roosting nests, as well as captive birds in a small heated chamber without a nest. In all cases, the birds called only at high temperatures, and even when they had no eggs in their nest, or no nest at all.
“That hot calls occur in a variety of contexts suggests it may be a widespread phenomenon in heat-stressed birds. Hot calls are therefore likely to happen in a wide range of bird species, although this remains to be established,” Dr Mariette said.
She said the results were important for understanding whether bird parents or embryos control development and suggest that embryos aren’t passive agents of their development under parental control.
“Instead, embryos pay attention to the sounds around them, to obtain information about the outside world that they will soon encounter. And our previous study shows that these external acoustic signals are sufficient for embryos to adjust their development to high temperatures,” she said.
The findings were also “very significant” for understanding the evolution of adaptation strategies to hot climates in birds.
“This new study shows that wild zebra finches, nesting in South Australia’s arid interior, also call when it is hot, just like birds kept in outdoor aviaries in Victoria,” Dr Mariette said.
The study also showed that heavier birds called at lower temperatures, presumably because large body size reduces heat dissipation efficiency.
“One very exciting question, however, relates to the function of calling for adults. We suspect calling is associated with a particular thermoregulatory behaviour, similar to panting, and we are currently investigating this question,” Dr Mariette said. The study, published in Scientific Reports in December was conducted by Dr Mariette and colleagues from CIE in collaboration with researchers from University of Wollongong and South Africa’s Pretoria University. Read it online at https:// rdcu.be/bc9kh