Like dutiful children, the embryonic chicks listen to their parents. But then it gets stranger.
Prenatal zebra finch chicks that hear their parents’ songs grow up to be, well, different from the other birds. It is unclear exactly how this happens, although researchers hypothesize that the birds’ developing brains may be altered by the sounds.
The songs seem to play a role akin to a meteorological warning, although the message plays out less like a forecast of tomorrow’s weather and closer to a long-term farmer’s almanac. The birds who heard the calls as embryos are better prepared to handle hotter habitats, according to a new study published in the journal Science by zoologists Mylene M. Mariette and Katherine L. Buchanan, both of Deakin University in Australia. That’s a spot of good news for animals destined to live on an overall warmer globe.
Zebra finches are one of the most well-studied birds in the world. Even still, they harbor their own secrets — like the songs sung to eggs, which had gone unnoticed until Mariette heard them while studying nesting finches in the wild. Such calls are “quite a difficult thing to spot,” Buchanan told The Washington Post by phone early Friday.
The sounds, which the researchers dubbed “incubation calls,” happen only intermittently and only under specific conditions. “The birds only seem to do it when they are inside the nest, and only when they are on their own,” Buchanan said. The sole possible audience for the incubation call were the eggs.
This discovery alone was new. Chickens and other poultry are known to communicate to their eggs, but it was a mystery if songbird embryos could hear anything going on outside their shells. There seems to be little doubt as to the finches’ target demographic: Zebra finches sang the incubation calls only when the eggs were close to hatching, within five days of a chick cracking through its shell.
Moreover, the incubation calls came only when the weather was hot. As the researchers wrote in their report, “zebra finch parents appear to control the production of incubation calls to signal environmental conditions to their embryos.” Taken together, the scientists do not believe the songs are triggered by increased heat alone — if it was warm outside but there were no eggs, the zebra finches did not sing their incubation song.
The researchers were left with another mystery. What purpose could these calls serve? To that end, they artificially incubated 166 zebra finch eggs at the same temperature, close to 100 degrees. Five days before hatching, the scientists played the incubation calls to a subset of the eggs. The other eggs heard simply normal adult chatter.
If the birds heard the incubation calls, they seemed better equipped to live in hotter habitats. They weighed less as adults and sought out warmer areas to build their own nests. “If they heard the call,” Buchanan said, “it set these birds on different trajectories for the rest of their lives.”
Although the long-term effects of these calls need more study, Buchanan believes the birds’ smaller size jibes with what biologists know about heat adaptation. There are a number of reports of animals getting smaller under climate change, she said, as it is proportionally easier to lose heat if you have a tinier body. Given the threat climate change poses to biodiversity, “that’s really encouraging,” she said. “There might be a subtle mechanism for animals to react to peaks in temperature.”
City University of New York animal behavior expert Mark Hauber said this study could change the way scientists understand how embryonic songbirds develop. “It’s so novel. It’s going to open up a brand new field of research,” Hauber told the Smithsonian Magazine. That the animals are being taught so much while inside an egg, he said, is a crucial new development.
Buchanan, too, is excited about what this discovery means for the science of finches. The birds play a crucial role in modern research. After the chicken, arguably the most important bird in human history, the zebra finch was the second bird to have its genome sequenced. Like small rodents, zebra finches often sub in for humans in the lab. But where rats or mice might mimic human behaviors such as addiction, zebra finches fill a slightly different role.
The birds are model organisms for what is known as vocal learning, the ability to hear and replicate a given sound. Humans and songbirds are some of the few animals that have the brain space dedicated to vocal learning (contrasted with your dog, who, although he might be able to understand “shake,” will never try to say it back). And if you want a robust language — to sing about how hot it is in here, for instance — you also need to be a vocal learner.