Baby birds start learning songs from inside their cozy eggs, study finds
Songbirds usually need very little instruction in singing their parents’ tunes, but the right melody doesn’t necessarily come to them “out of the blue” when they hatch.
Instead, a new study suggests that most chicks begin to listen to and respond to the song of surrounding birds as mere embryos, while still nestling in their eggs.
Even when a species is considered an “innate” songster – with the proper genetics and brain wiring to produce its species’ song once hatched – researchers have also found evidence of embryonic learning.
With enough time and repetition, it seems that unhatched chicks usually get used to noises coming from outside their shells, which is an important part of their vocal development.
“Long before actual vocalization, we discovered that these tiny songbirds also discriminated against non-specific sounds and were capable of” non-associative “(not parental) sounds, relying on the complexity of vocal learning in songbirds, ”explains animal behaviorist Diane. Colombelli-Négrel from Flinders University in Australia.
According to historical classification, birds (and other animals) are either vocal learners, able to invent new songs or imitate those of others; or non-learners, stuck with their “innate” repertoires that stem from brain wiring and genetics.
In recent years, however, researchers have started to argue that this binary vocal learning system in vertebrates is too simplistic, and we are in fact dealing with a spectrum or a continuum.
At one end of the spectrum is a high degree of vocal learning, with species able to mimic all kinds of new sounds – many songbird lineages fall into this category, as do humans. On the other hand, you get the relatively limited non-learners, who can only produce sounds of their own kind, and nothing else.
The rest of the birds fall somewhere along the continuum of learned and un-learned vocalizations and sometimes it’s hard to tell the difference between the two.
Even among “acoustically naive” songbirds, which have received little or no vocal instruction, studies have shown that sounds from their own species elicit a stronger neural response than song from an alien species. .
This suggests that baby birds acquire a “voice pattern” in their brains long before they hatch, and new research on bird embryos now supports this idea.
Over the course of seven years, between 2012 and 2019, researchers played a variety of bird calls to eggs from five different bird species.
These included the superb fairy troglodyte (Malurus cyaneus), the red-winged wren (Malurus elegans), Darwin’s Lesser Land Finch (Geospiza fuliginosa), the little penguin (Eudyptule minor), and the Japanese quail (Coturnix japonica domestica).
Darwin’s Wren and Finch are considered vocal learners, while Quail and Penguin are generally classified as non-learners. In the first part of the experiment, the researchers exposed 109 embryos to 60 seconds of noise, limited by 60 seconds of silence.
Compared to embryos from non-learners, such as penguins and quails, the authors found that embryos from vocal learners showed a more precise response to the call of their own species at a much earlier stage of development.
This was expected, as recent studies have shown that vocal learners, like zebra finches, can see their behavior as adults altered by the songs their parents sing to them as embryos. Non-learners, on the other hand, don’t seem to have such malleable brains. But that doesn’t mean they don’t absorb any song when they’re in the bud.
In the second part of the experiment, the researchers exposed 138 embryos to 180 seconds of the same bird song, their own species or another, again locked in a minute of silence.
This time, the heart rate of each embryo was measured to determine the attention the baby bird was giving to the repeated call.
Ultimately, the authors found that all birds, learners and non-learners alike, had become accustomed to the repeated external sound, whether from their own species or from a different species.
This indicates an innate level of learning known as habituation, which might help animals distinguish between friendly calls and calls from another.
“The results of this study suggest that the ability to perceive and become accustomed to sound in ovo in developing birds may be taxonomically more widespread than previously thought and also support the idea that learning speech perception is not a binary behavior, ”the authors write.
It is still unclear whether this initial embryonic learning alters the behavior of birds once hatched, but the authors suspect that sound may begin to prepare embryos for life outside of the egg, albeit in a slightly different way with a slightly different timing depending on the species.
For example, studies have already shown that unhatched embryos of some gulls can hear their parents’ warning calls. Additionally, when these same birds are born, they tend to exhibit more defensive behaviors, higher stress levels, and are particularly sensitive to red flags.
More research will be needed to compare the impact of sounds drifting through an eggshell on vocal learners and non-learners as they grow older.
“This research will hopefully inspire more studies on the remarkable ability of animals to learn sound,” said systems biologist Sonia Kleindorfer of Flinders University and the University of Vienna.
“By shifting the time window for sound learning at the prenatal stage, this direction of research opens avenues for measuring the downstream neurobiological effects of early auditory experience on behavior and information processing.”
The study was published in Philosophical Transactions of the Royal Society B Biological Sciences.