Baby Birds Learn Calls From Their Mothers While Still in the Egg

Rather like an expectant human mother playing Mozart to her unborn child, some mother fairywrens call softly to their eggs. Now, two recent studies conclude that two species of fairywrens can hear their mothers and even learn elements of her calls while still inside the egg.

Imitating their mother’s calls may ensure they are fed as nestlings, helping to distinguish them from the cuckoo nestlings that sometimes show up in nests. Retaining key elements of her call throughout their lives may also serve as a family “password” long after the young have grown and are raising chicks of their own.

Fairywrens are small Australian songbirds. Nine species occur on the continent where they can be common suburban birds, in places as familiar as chickadees are in the U.S. The males are often brilliantly colored in glittering blue or red, and the species’ unusual breeding habits have made their behavior a popular research topic for decades.

A series of experiments on Superb Fairywrens led by Diane Colombelli-Négrel and Sonia Kleindorfer of Australia’s Flinders University suggested the embryos were learning while still in the egg—contradicting a long-held view that embryos have limited learning abilities. Even among humans, it’s only been in the past few years that research has shown an unborn baby can begin to learn the sounds of speech when it is 30 weeks old.

“It took us nearly four years to convince other people that this is happening” in fairywrens, said Colombelli-Négrel. “Finding [vocal embryonic learning] in an animal, especially a songbird was pretty fantastic.”

Experiments with Superb Fairywrens showed the embryos lowered their heart rates when listening to the soft calls produced by their mother during incubation, a sign of attention in humans and other animals.

Because the finding in Superb Fairywrens was so unexpected, Colombelli-Négrel and colleagues expanded the research to include a separate species, the Red-backed Fairywren. That’s when Cornell Lab of Ornithology researchers Jenélle Dowling and Mike Webster joined the team.

Colombelli-Négrel and colleagues used microphones at 67 Red-backed Fairywren nests over a 4-year period to capture the soft calls the mother birds made to their eggs. The calls began soon after laying and continued for several days after hatching.

“The sounds the mom makes to the eggs sometimes sound like a spaceship—it’s a really interesting sound, really varied with lots of modulation,” Dowling said.

Calls given by a mother Red-backed Fairywren during incubation

Soon after hatching, the chicks start begging for food, reproducing some of the same sounds they heard in the egg. But the researchers still had a question to settle: had the chicks really learned their mother’s calls, or did they make the sounds instinctually?

“To determine if this was actual learning versus genetic predisposition, we switched Superb Fairywren eggs among nests,” Colombelli-Négrel said. “When the chicks hatched, they produced calls more similar to those made by their foster mother than their genetic mother, which shows they had been listening in the egg.” Subsequent experiments with Red-backed Fairywrens found that parents gave more food to nestlings that had calls similar to their own.

“Learning calls in the egg is like an elegant password system that mothers may use to assure they are raising their own chicks,” Dowling said. “Cuckoos often leave their eggs in a fairywren nest. If a nestling can’t reproduce the mother’s signature sounds, it could be a cuckoo chick and it might not get fed.”

Next, the researchers investigated whether the calls the chicks learn in the egg are retained in their adult songs, the songs they will sing for the rest of their lives. This investigation challenged the conventional assumption that chicks do not begin to learn their adult songs until they are at least 10 days old. Because human ears are not up to the task of parsing the frenetic burbling of fairywren song, the researchers used spectrograms and computer analysis.

Mother’s Full Song

Son’s Full Song

“We compared every element sung by adult offspring to every element sung by mothers in the population,” Dowling said. “We used a computer technique called dynamic time warping, which compares and aligns song elements at various time points. This provides a score for how similar the two elements are. The scores showed that each young bird’s song was more similar to its mom’s calls than to calls of any other female in the population.”

In other words, even as adults, the Red-backed Fairywren offspring kept the key similarities to their mother’s sounds. This too has benefits.
Dowling said, “This whole field of study falls into the area of ‘kin recognition’ in which the birds may know who is related to whom because of these acoustic signatures. Kin recognition is important because birds and other animals tend to give preferential treatment to individuals they can identify as relatives, by providing information about food and warning of a predator nearby. It also helps to avoid inbreeding.”

Since embryos learn their mother’s calls, and seem to reproduce them in their adult songs, this suggests that they start learning their adult songs while still in the egg. The fairywren research opens the door to all kinds of explorations into embryonic learning in other species of birds and mammals, and studies of when signals for kin recognition develop.