Birdsong and Dialect

A young sparrow raised where it can hear nothing produces a song that is recognisably its species and recognisably wrong. It has the general shape and none of the detail. Raised within earshot of adults, it acquires the local version, and the local version differs measurably from the one sung twenty miles away. Both facts have to be accommodated at once: the outline is inherited and the particulars are learned.

[A] What makes the case useful is that the learning has a schedule. [B] There is a period early in life during which the bird takes in songs it will not produce for months, and once that period closes it can add nothing further. A bird moved to a new valley in its first summer sings like its neighbours; a bird moved a year later sings like a stranger for life. [C] It would be convenient to conclude that the dialect is therefore a passive record of where a bird spent one season, and the field data resist that. [D] Females in several species prefer the local dialect, which gives the learned detail a consequence, and males on the edge of two dialects sometimes hold both and deploy them separately. A trait learned in a fixed window can still be used with something that looks like judgement.