Cuckoos are on the way! Satellite tagging by the British Trust for Ornithology has revealed their extraordinary journey. Cuckoos spend the winter with lowland gorillas in the African Congo rainforests. They leave in early March and fly to West Africa, where they fatten up in preparation for the crossing of the Sahara. They then endure a 50-60 hour non-stop flight over this vast desert. After recuperating on the shores of the Mediterranean, they continue north through Europe, reaching Britain towards the end of April.
The male’s familiar call – “cuckoo” – has been our welcome harbinger of spring for thousands of years. But for many other birds it signals impending doom, for the cuckoo is Nature’s most notorious cheat. At each nest she parasitizes, the female cuckoo lays just one egg. Soon after it hatches, the cuckoo chick ejects the host eggs and any host young out of the nest. I have seen this many times now, but it always amazes me. Often, the host parents are at the nest and they simply stand by and watch. Every summer, thousands of small birds will have their eggs and chicks tossed aside by young cuckoos. The hosts then spend the season raising a cuckoo chick rather than a brood of their own. For me, as a naturalist and scientist, the call of the cuckoo has been an invitation to solve an enduring puzzle: how do cuckoos get away with such outrageous behaviour?
Newly-hatched cuckoo chick ejecting a reed warbler’s egg (Photograph taken by Richard Nicoll) .
The sight of a little warbler or pipit feeding an enormous cuckoo chick makes you wonder if the hosts have any defences at all. But our field experiments show that most hosts are well aware of cuckoos as a threat. They mob adult cuckoos and reject eggs that differ from their own in colour or markings. To succeed, the female cuckoo needs secrecy to avoid alerting the hosts and an egg that mimics the host’s eggs. The cuckoo chick then manipulates its foster parents into bringing as much food as they would to a brood of their own young by an extraordinary begging call – a rapid and high pitched series of notes that sounds just like lots of hungry host young.
Reed warbler feeding a nine-day-old cuckoo chick (Photograph taken by Richard Nicoll) .
We may pride ourselves that we would not be manipulated so easily. But advertisements do this to us every day. A recent study reveals that we are more likely to obey a notice if it has an image of a pair of eyes. I imagine having a conversation with a reed warbler. “Why don’t you realise that that’s a cuckoo chick?” I ask. And it replies: “Why don’t you realise that no one is watching you? Those are just pictures of eyes.” Watching hosts being tricked by cuckoos is a reminder of our own vulnerability, too.
Meadow Pipit feeding a fledgling cuckoo (Photograph taken by Charles Tyler)
This is a guest blog from Nick Davies, author of Cuckoo – Cheating by Nature. His brand new book (out last week) offers a new insight not only into the secret lives of these extraordinary birds, but also into how cheating evolves and thrives in the natural world.
“This amazing detective story by one of the country’s greatest field naturalists is also a fascinating study that solves many of the puzzles surrounding this most extraordinary bird” – Sir David Attenborough
“A new book tells in mesmerising detail how the host birds are first outwitted by the female cuckoo, and then by the cuckoo chick … A riveting account not only of how the cuckoo evolves deceptive stratagems, such as eggs which mimic the eggs of the host, but also of how the host birds evolve defences, such as learning to reject any eggs which seems slightly different from their own. This is in effect an “evolutionary arms race” and its complexities are elucidated with exemplary clarity and humour by Professor Davies … An even more fascinating take on curious behaviour … It’s a terrific read” – Independent
“Charming … Reveals how Wicken’s reed warblers are locked in an evolutionary arms race in The Fens with the female cuckoo” – Daily Express