AS the US writer Nora Ephron wrote in the movie Heartburn, 'If you're looking for monogamy, you'd better marry a swan'. Some species of bird do, indeed, pair for life, yet other species including most songbirds are 'socially monogamous'. This means that, although they will form a pair for the entire breeding season, to help one another raise their young, the male (and, often, also the female) may also sneak off and try to mate with other birds.
In the male's case, this strategy is likely to mean he will have more offspring-even if he might never see some of them. For the female, mating with two or three males does not increase the number of chicks she can have, as she will still lay the same number of eggs. However, by mating with several males, she does benefit from having a range of young with different genetic qualities inherited from their fathers, some of which will be more likely to survive than others. This avoids, as it were, putting all her eggs in one basket.
Birds pair up by using two basic techniques. Songbirds, which make up more than half of all the world's bird species, have (as their name suggests) an attractive, tuneful song. This is almost always uttered by the male and serves two purposes: to attract and keep a female; and, at the same time, to warn nearby males to keep out of his territory and away from his mate.
Many larger birds, whose vocal talents are more limited, use a visual courtship display instead. This can be something quite basic, with the male simply showing off his attractive plumage to the female. Although it can also evolve into a truly memorable routine, in which both the male and female perform a complex series of dance moves, often exactly mirroring one another's movements. For humans, our own abilities to sing and dance were originally influenced by these incredible natural sounds and sights.
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