Study

Song learning, early nutrition and sexual selection in songbirds

Nowicki, Stephen; Peters, Susan; Podos, Jeffrey

American Zoologist, 1998

Peer-reviewednarrative reviewmixed

What they did

Sets out and reviews evidence for the proposal that song learning is costly and occurs while the brain is still developing, so that nutritional or other stress in early life leaves a measurable mark on adult song — including experiments in which young birds were reared on restricted diets.

Studied in: Passeriformes
Sample size: synthesis with supporting nutritional manipulation experiments

What they found

Birds subjected to nutritional stress during the song-learning period produced poorer copies and, in some species, had smaller song-control brain regions, with the deficit still detectable in adulthood.

What it means

The authors' reading, and ours. Where they differ, that difference is the point.

How the authors put it

Song functions as an honest signal of developmental history because learning it well requires a brain that developed well, which requires having been adequately fed as a nestling.

How NatureHQ reads it

This is the best available answer to a question the function literature tends to skip: why would song be worth attending to at all? A trait is only a reliable signal if it is hard to fake, and a song learned during a window when the brain is still being built cannot be improved later by an adult in good condition. The hypothesis is well supported for the existence of the effect and much less well supported for the claim that females actually use it, which is the step most popular accounts take for granted.

Limitations

Evidence that early stress degrades song is far stronger than evidence that receivers use song to assess it.
Effect sizes and even direction vary between species and between the specific song features measured.
Nutritional restriction in the laboratory is a blunt manipulation standing in for a wide range of natural stressors.