The Cuckoo Comes in April

The Common Cuckoo, Cuculus canorus, has one of the most recognisable calls of any bird in Britain. Perhaps it is no surprise then that there are numerous references to it in literary works from the Middle English “Sumer is Icumen in” to Shakespeare’s springtime song in “Love’s Labours Lost” and the well known old country poem:

The Cuckoo comes in April,

sings his song in May,

changes his tune in the middle of June,

and in July he flies away.

It has even been used in more modern popular culture, adapted for use in a song by Simon and Garfunkel, and the Cuckoo has long been heralded as the harbinger of spring.

It’s not quite correct because that change of tune mentioned is in fact when the male stops calling for a mate and the female’s bubbling call is heard instead. This call is an extraordinary mimic of the Sparrowhawk’s call, employed along with their plumage, to ensure that the owners of the nest they intend to lay their eggs in don’t return during the act of laying. Using a host to raise their young allows female Cuckoos to lay far more eggs than a conventional brood, with a single female laying up to 25 eggs in a season.

Thanks to satellite tagging projects such as that run by the British Trust for Ornithology, we now also know that males can leave on their return migration to sub-saharan Africa as early as mid June with females generally following suit a week or two later, their egg-laying duties completed and with no parental responsibilities. Their routes can be tracked too, showing that while there are two routes taken northbound, they all return south the same way making a round trip averaging 10,000 miles each year.

Their young will be raised by unwitting hosts many times smaller than the growing nestlings. These are most commonly Reed Warblers, Dunnocks and Meadow Pipits in the UK, although on the continent other species are targeted as well including most commonly Robin, Pied Wagtail, Garden Warbler, Great Reed Warbler, Redstart and Brambling. This interesting since each female Cuckoo will usually favour the same host species as its mother because it will be genetically favoured to produce eggs with similar markings to that species, giving its offspring a greater chance of survival as its hosts will not be able to detect the eggs as different to their own in the nest.

This whole process has been described as an evolutionary arms race – the hosts evolve to become better at detecting the Cuckoo’s deception while the Cuckoo evolves to become better at  deceiving their hosts. This is not just the case with our Common Cuckoo either. There are 150 species in the family Cuculidae, although many raise their own young.

It won’t be long before these incredible long distance travellers will be heard across the British countryside for another spring-summer season. While we have learnt a lot about them, there is still much that we don’t know – such as how the young birds know where to go for the winter without their parents to guide them on their first migration. The natural world has much to teach us and many secrets to yield if we can conserve it for long enough to learn them.

If you’re interested in learning more about both the Common Cuckoo and other members of the Cuculidae family, you might like to read “Cuckoo: Cheating by Nature” by Nick Davies, the foremost expert on these incredible birds.