For generations, the more sentimental among us have seen the onset of spring and the mating activities or birds as a pointer that romance and new beginnings are in the airIt is true, of course, that some bird species are faithful to one partner throughout life. There is no better example than the Mute Swan. Pairs stay together nesting on the same patch of riverbank for years, and only if one of the pair is killed will the other search out a new mate. Pigeons also tend to stick with the same mate - but the picture elsewhere is one of utter debauchery!

The Dunnock, Hedge Sparrow or Hedge Accentor, is a pretty uninspiring species. It creeps around hedge bottoms rather like a small mammal searching for food, only occasionally perching aloft and uttering a tuneless song. It's brown and grey plumage gives no clue to the shameful goings on of the female Dunnock, who actually has a sensible strategy to ensure she raises healthy young. Each spring she finds an old and trusted male, courts him, and mates successfully. Next she creeps off to another part of the garden and finds a much younger toyboy male, and mates again. Then she lays four brilliant blue eggs, each pair having a different father.

Smaller species live very short lives, so tend to take new mate each year. This is often necessary for migrants to Africa where many birds perish both on the winter grounds and during migration. Welsh specialities like Redstarts and Pied Flycatchers need to make the most of the British summer and, to exploit this, males are often polygamous, mating with at least two females, and sometimes having broods with each.

One Welsh songster, the Wood Warbler, is just as polygamous and possibly even more cunning. Chris Mead, a leading ornithologist who died recently, once suggested something quite amazing. The bird has two distinct songs - a rattling trill and a very different repetitive flutey note. Chris reckoned it would trill away to get one female on eggs and then go off singing his second song to attract another lady so the female would not realise he was being unfaithful!

Mistle Thrushes desperate to get the best females use food to attract their attention. A male will stake his claim on a fruitful berry bush, in the hope of enticing a mate with the promise of a substantial food store for the winter and coming spring. To this bird, sex and food are equally important.

Some of our shorebirds breeding in the far north are even more inventive. Phalaropes and the Dotterel have a completely reversed strategy largely because these birds have to produce as many young as possible from an incredibly short summer. In most birds the male is the dandy with bright colourful plumage, while the female is duller to give her maximum camouflage when she is on the nest. In Phalaropes and the Dotterel, the female is bright and gaudy and the male much duller. Females unashamedly gather one or two males around them, copulate with each and lay a clutch for each male. Each male incubates his clutch and brings up the brood, while the female takes no part in the process.

Specific breeding strategies have evolved over thousands of years and are essential for the survival of these species. So next time you start thinking about birds pairing up for a faithful marriage, just think again. What they're doing might not be romantic, but it is very, very practical.

Derek Moore, February 2003