Children often notice more than adults think they can. Hardly any information that is shared in the presence of the little ones and that is relevant to them escapes their ears – even if they do not let it be seen from the outside that they are listening. It seems that little birds that are still sitting in the egg achieve a special mastery. The unhatched chicks not only hear noises from their environment, but also learn the typical song of their species in the egg – months or even years before they themselves produce the complex tone sequences as adults. This is what a team led by the biologist Diane Colombelli-Négrel from Flinders University in Adelaide, Australia, wrote in the specialist magazine Philosophical Transactions.
Finches and little penguins were among the study participants
The authors sonicated the eggs of five different bird species with recordings of native and foreign sounds. Of the five species, three – small-ground finch and two staggered tails – are so-called vocal learners. These are birds that have an innate preference for the singing of their own species, but are largely guided by their environment when it comes to the subtleties of vocalizations. In order to be able to communicate efficiently later, they need role models. This means that these species are members of a rather exclusive circle: not too many animals have been trusted to learn vowel so far. It is secured – except for songbirds and humans – for example with parrots, bats and whales.
The chicks of little penguins and Japanese quail also took part in the study. Both are not songbirds. But precisely because of this, the experiments with these two species provided an interesting finding. Even chicks that are not dependent on learning a certain song can perceive the vocalizations of their conspecifics already in the egg and learn them easily. The authors derive the latter from recordings of the heart rate of the small birds. Initially, the heart rate increased in all chicks as soon as they were exposed to sounds from representatives of their own species. However, this reaction weakened after a few repetitions in all of the species examined. For biologists, this is evidence of so-called habitual learning – that is, of getting used to it. In view of these results, the authors advocate dividing the animal world into a less binary division into vocal learners on the one hand and vocal non-learners on the other.
However, differences between the tested songbirds and the other two species were also clearly evident in the study. The chicks of the three songbird species initially reacted more strongly to the singing of their conspecifics than the penguin and quail babies. So, based on genetic and neurological predisposition, they recognized that these special tones are of particular relevance. In addition, the heart rate increased to a lesser extent – only in the songbirds – when they heard strange singing. This reflects the fact that the chicks have to gain experience with their noisy environment in addition to their genetic disposition in order to learn how to sing correctly. So far it was not known that this learning begins in the egg. Presumably the early experiences influence the further development of the gene activity and the neurological interconnections in such a way that the chicks become more and more attentive to the singing of their own kind, write the authors. Depending on how limited or varied the singing backdrop of the chicks in the egg is, their later singing repertoire could also be limited or variable.