Zoology Notes 002: The aquatic warbler, an exponent of prolonged sex

The aquatic warbler, the bird with the longest staying power, as depicted by Danish naturalist and artist Henrik Grönvold Photograph: The British Warblers: A History With Problems of Their Lives. The Internet Archive

In most bird species, copulation is a flighty affair, lasting little more than seconds. But the secretive aquatic warbler, which winters in Africa and breeds in the marshy fenlands of central and eastern Europe, goes in for extraordinarily prolonged copulation. In the 1990s, researchers studying a population of captive warblers observed males staying mounted for an average of 24 minutes. In one instance, the male stayed on top for a record-breaking 50 minutes. During this time, he repeatedly connects with the female and makes several inseminations.

This peculiar behaviour is likely bound up with the aquatic warbler’s unusual mating system. Unlike most other passerines, males and females meet only to copulate, with the female subsequently rearing broods of two to four chicks as a single parent. In the absence of significant social bonds, females are free to mate with several males and do so, almost two-thirds of nests containing offspring with different fathers. Prolonged copulation might be down to the male trying to monopolise the female. But since females are free to escape the male at any time, prolonged copulation is more likely to be part of a female strategy to control who fathers her offspring.