Photograph of a white-crowned sparrow, courtesy of F. Goller, University of Utah, USA.

New results published in Nature show that songbirds can accomplish remarkable feats of learning, at least when it comes to learning to sing. Rather like sequencing a genome by shotgun sequencing — splitting the genome into fragments that can be easily sequenced and then put back in the right order — white-crowned sparrows can learn their songs in pieces.

Shotgun sequencing requires a computer to reassemble the short sequences into the correct order by matching overlapping segments. Rose et al. show that white-crowned sparrows are capable of a similar feat when it comes to learning their song: after being exposed only to short but overlapping snippets of a 'tutor song', the young songbirds can reproduce the full tune. Beyond the remarkable animal behaviour story, the results offer insight into how the brain might store auditory memories that guide learned vocal behaviour.

The authors collected nestlings and exposed them to a recorded tutor song from the age of about 10 days. The researchers deliberately fragmented the recordings, so instead of a usual white-crowned song — which consists of four or five ordered 'phrases' of whistles, trills, buzzes and so on — the young birds listened to pairs of normally adjacent phrases. For example, if a full song consists of ABCDE (with each letter representing a phrase), the birds might have heard DE, CD, BC and AB, with silent intervals separating the phrase pairs.

Rose et al. found that birds tutored on only adjacent phrase pairs could produce a normal, correctly ordered song, akin to singing 'Mary had a little lamb' correctly after only having ever heard 'little lamb' 'a little' 'had a' and 'Mary had'. Furthermore, in a separate experiment in which birds were tutored with reverse-order syllables (BA, CB, etc.) the birds learned to sing a fully reversed song (EDCBA). This latter result is even more remarkable in light of previous evidence that white-crowned sparrows have a strong innate tendency — even in the absence of any tutor — to start songs with 'A-like' introductory phrases. The authors confirmed that the overlapping phrase-pairs were essential, as birds that only heard single phrases — even though they heard all the phrases — could not sing normal songs.

During vocal learning a bird forms an auditory memory or 'acquired template' of the tutor song. However, how the nervous system stores such a long-term auditory memory, and how this template guides subsequent vocal learning, has remained largely mysterious. Rose et al. now show that the template need not be a representation of the full song. Instead, based on their behavioural data, they propose that a population of phrase-pair detectors might be adequate. Evidence for neurons that might serve as such detectors already exists, so the behavioural results are certain to spur further research into the neural basis of vocal memory.