Researchers identify an “adaptive function for prenatal communication.”
Chick embryos, still encased in their eggs, can hear the sounds of their parents chirping. And according to a new study published in the journal Science, mother and father zebra finches take the opportunity to warn their unhatched chicks about the extreme heat they will soon face.
When wild-caught zebra finches were alone with their soon-to-hatch eggs in an outdoor aviary, Mylene Mariette and Katherine Buchanan, from Deakin University in Australia, observed that they produced “incubation calls,” but only when temperatures rose above 26 degrees Celsius (78.8 degrees Fahrenheit).
To see if those calls were somehow preparing the offspring for the heat, the researchers recorded some of the calls and then played them to eggs that were kept at a standard temperature. Once hatched, the birds were raised in nests of varying degrees of warmth.
The incubation calls did appear to have an effect on the nestlings, but perhaps an unexpected one. The researchers found that nestlings that had been exposed to the calls as embryos ended up weighing less than control nestlings.
Being small may seem detrimental for these birds, but the researchers figured it might actually benefit them in a hot environment because slower growth would reduce the buildup of cellular damage, and little animals tend to be better at dissipating heat.
Once they reached adulthood, the females that had been small and were raised in hot nests actually produced more offspring than others, confirming that the combination of puny size and high temperature was beneficial in the long run. Their parents had prepared them well.
Further, the incubation calling may have permanently altered the birds’ sensitivity to heat, as males that had heard the calls as embryos tended to seek out hotter microclimates as adults.