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OBVIOUS BIRDS #76: Cuckoo (Cuculus canorus)

By alicebg, Aug 3 2017 07:05PM

(image courtesy of thebritishbirds.com)


Definitely an obvious bird, the Cuckoo has as high a profile as any avian in the UK. A migratory avatar of spring, celebrated in words and music and studied to the nth degree, its strange whooping call familiar to everyone, even those who have never heard it live. None of this, however, should distract from the fact that the Cuckoo is by far Britain's strangest bird.

The reason the Cuckoo has not already appeared in this list is its unexpected and alarming decline in England. In my specific case that has meant an absence of both sight and sound for several years. I am pleased to report that drought was broken in 2017, with a reappearance on my local marsh - hopefully a positive sign. While Cuckoos were never exactly plentiful on my patch, they were certainly a regular feature of marsh, woodland and even coast.

When they are around, Cuckoos are easy - and genuinely unmistakeable - to hear, but actually seeing them takes patience. When you do, they're always a bit of a surprise, looking for all the world like a squashed Sparrowhawk. This, evidently, is a specific adaptation intended to trigger precise responses in the Cuckoo's target birds. For while the Cuckoo is no raptor, it does employ a bizarre strategy to thrive at the expense of other species.

Cuckoos practise 'brood parasitisation' - that means they lay their eggs in other birds' nests and rely on the surrogate parents to raise their young, with whom they will never interact. The newly-hatched Cuckoo chick instinctively ejects any other eggs from the nest, making itself the sole focus of the surrogates, who tend it as their own even when it grows monstrously larger than themselves. Birds targeted this way include Dunnocks, Skylarks and Warblers, among others.

Cuckoos are by no means the sole practitioners of this curious activity, but they are the best-known by far. Such behaviour, while insidious by human standards, is fascinating from a biological and evolutionary point of view, and begs many questions for which there remain no clear answers. How did Cuckoos evolve such a reproductive strategy? If the Cuckoo chick can imprint itself upon its 'parents', why isn't the reverse true, ie how does a Cuckoo know it's a Cuckoo, having never interacted with another Cuckoo? And can targeted species resistance to this parasitisation (recent research indicates that they can)? Science may eventually answer these questions, but for now we can only savour the presence of this lauded, fascinating and frankly rather insidious creature. And let's hope that decline reverses soon.

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