The division of bird vocalisations into songs and calls is long-standing and widespread, despite difficulties with definitions and assigning vocalisations to one category or the other.
In general, a call is a vocalisation of short duration that is simple in its structure and as likely to be uttered by a female as a male. In contrast, a song tends to be more complex in its structure of longer duration and is usually uttered by a breeding-age male.
Calls are typically produced under particular circumstances (during courtship or aggression, say, or in response to the sighting of a predator), and a species may have a vocabulary that is made up of a number of different calls. Many small birds, for example, have a dozen or more recognisable calls. Calls, being short and simple in structure, convey only a small amount of information.
But complex song carries more content, and is primarily used by males to identify territorial ownership and to signal information about the singer, at least some of which may influence his chances of attracting a mate. Some ‘calls’, such as the ‘twit-tw-oooo’ of the tawny owl, have the same purpose as ‘songs’, underlining the problems with the definitions we sometimes use.
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Main image: Wren singing. © BirdImages/iStock