The host may recognise the intruding egg and abandon the nest, or it may incubate and hatch the cuckoo egg. The European Cuckoo, whose distinctive call is immortalised in the sound of the cuckoo clock, is the bird in which this habit has been most thoroughly studied.įemale European Cuckoos lay their eggs only in the nests of other species of birds.Ī cuckoo egg usually closely mimics the eggs of the host (one of whose eggs is often removed by the cuckoo). Some species of birds thrive not by carefully rearing their own young, but by pawning that task off on adults of other species. They've also evolved the ability to make their own eggs more distinct, covered with unique patterns and colours, to help ensure they don't confuse them with foreign eggs.īut over time, the parasite species evolves so their eggs better mimic the host – and so the 'evolutionary arms race' continues.Ī reed warbler (right) with a tasty morsel in her beak and for a very large and deceitful cuckoo chick (left) Hosts can detect the foreign eggs and eject or abandon them. Over the course of several decades, this has created what Professor Davis calls an 'evolutionary arms race' between the host and the parasite.įor example, African finch chicks (a parasite species) have evolved tiny details on the insides of their mouths to mimic those of their host species, the grassfinch, a study showed last year. When hatched, some species, like the cuckoo, kill the rival birds - and the unsuspecting mother's true offspring - by kicking them out of the nest and reap the benefits Some species of birds discreetly place their eggs into the nests of other species so the mothers effectively raise their offspring for them. Interestingly, bird 'hosts' that are victim to brood parastism every year have evolved various tactics to detect the parasite's eggs and save their own eggs from being murdered.Ī larger 'parasitic' purple indigobird nestling (right) alongside its two jamesons firefinch host chicks - and rivals. One photo, like something out of a horror film, shows a greater honeyguide chick attacking much smaller chicks of the host species, the little bee-eater. Professor Claire Spottiswoode, co-author of this new study and one of Professor Davis' colleagues at the University of Cambridge, has snapped some amazing photos of brood parasitism in action on location in Africa. More photos of a small reed warbler parent feeding a huge cuckoo chick that emerged last year are both tragic and perversely comic. 'The host parents are then tricked into spending their summer raising a cuckoo instead of a brood of their own chicks.' 'Every summer, thousands of small birds will have their eggs and chicks tossed overboard by young cuckoos,' Professor Davies wrote for the Daily Mail. Perfectly illustrating his description, images emerged in 2018 of a dunnock, or hedge sparrow, that had been duped into feeding an enormous cuckoo chick. Professor Davies is the author of several books on the cuckoo and brood parasitism in birds, including Cuckoo: Cheating by Nature, published in 2016. The bizarre scene is the result of the cuckoo’s sneaky habit of laying eggs in the nests of other species and leaving the unwitting birds to raise their chicks. A reed warbler (left) and a very large and deceitful cuckoo chick (right) They did this by beaming infrared light through the egg and recording when that beam was disrupted – an indicator of movement. The academics measured embryo movement (when the birds were still in the egg, unborn) in multiple brood-parasitic and non-parasitic bird species. Host species, meanwhile, included the great reed warbler (Acrocephalus arundinaceus, one of the cuckoo's preferred hosts) and the common waxbill (Estrilda astrild). Parasite species included the common cuckoo (Cuculus canorus), the brown-headed cowbird (Molothrus ater) and the lesser honeyguide (Indicator minor). Others have evolved a dangerously sharp point on the end of their little beak, which they use to pulverise the eggs of their host (in the case of the greater honeyguide and lesser honeyguide).įor their study, McClelland and colleagues studied movements in 437 eggs from 14 species of birds – hosts, parasites and other bird species as a comparison – from three continents (Europe, America and Africa). 'It's like a newborn baby lifting a bowling ball,' study leader Stephanie McClelland, a biologist at the Royal Holloway University of London, told The Atlantic. Some brood parasite chicks, including the cuckoo, push the host's eggs out of the nest one by one, in an impressive display of physical exertion.
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