The Fascinating World of Cuckoos: A Closer Look at Their Mysterious Behavior

The cuckoo’s annual visit to Ireland is coming to an end. You may hear his magical song up to the end of the month, but seldom later than that. The best-known sound in all of nature everyone, even the most musically challenged, can recognise it effortlessly. But there’s a paradox here; few people have any idea what the singer looks like.

As children growing up in Limerick city, we would hear the two-note song. I remember trying to catch a glimpse of the caller but to no avail. The cuckoo pulls off an extraordinary feat; he produces the clearest of far-carrying sounds while, at the same time, keeping a tantalising low profile. A vocal ‘slight of hand’ is being perpetrated.

Nor is the singing male a flashy dresser. The size of a mistle-thrush, he sports a grey head and upper parts with barring on the belly. The female is slightly smaller. Both sexes have long tails, rendering them easily mistaken for sparrow hawks in flight. This strange bird, which ignores the ordinary decencies of family life, seems both to love and shun the limelight. Why has it such an apparently contradictory character?

We call it the ‘European’ cuckoo, but it’s actually an African bird which spends about a third of its year in the northern hemisphere, arriving in Ireland from late April. Laying eggs in the nests of gullible small birds and duping them to raise your young is a complex operation in which the male and female cuckoos play very different roles.

The newly-arrived male cuckoo is only weakly territorial. Unless there are potential rivals in the vicinity, he establishes only a loose ‘home range’, really a ‘song range’, at the fringes of which he tolerates other males. He sings to impress and vies with his rivals to draw in and court females. A hen will usually have several partners during the egg-laying season.

The small birds, whose eggs and chicks, will become the cuckoo’s victims, know the song. ‘Cuckoo cuckoo, oh word of fear, unpleasing to the married ear’, said the Bard. They will club together to harass the singer, so he keeps a low visual profile.

The female has a very different perspective. She must find an area where many small birds are nesting. She could lay in any nest, but she has a species of choice, whose eggs, through natural selection, her own eggs are similarly marked. ‘Banaltra na cuaiche’, which the cognoscenti will know means ‘the cuckoo’s nurse’, is the desired species in Ireland. It’s the meadow pipit we used to call the ‘tit-lark’.

Hers is no easy task. She could lay up to 25 eggs, although the average is about nine. Each egg is deposited in a different nest, so this supreme bird-watcher monitors the activities of potential host pairs carefully to find the locations of their nests. Then she needs to calculate their likely laying dates. When the victim parents are away feeding, she flies to their nest, removes an egg, and lays one of her own, all in less than a minute.

Some insect and fish species, as well as cuckoo and cowbird species indulge in this ‘brood-parasitism’. In none, however, is the practice as extraordinarily developed as with our European cuckoo.

Nick Davies. Cuckoo, Cheating by Nature . Bloomsbury. 2015.