It’s no news that cuckoos are brood parasites: they lay their eggs into the nests of other bird species – a clever trick that spares the rearing and feeding of own offspring. We’ve all heard the story. But why do other parent birds let this happen? Are they too stupid? Too inept? Or simply clueless? Admittedly, cuckoo’s eggs do usually look deceptively genuine. But the cuckoo chick? Not even remotely! It quickly grows into a giant that looks nothing like its new family. So why don’t the adoptive parents notice the sham then?

Some cuckoo chicks even go as far as to kill the other chicks in the nest. In most cases, however, they just smuggle their eggs into the nests of other birds, some of which are intelligent enough to spot this easily. Still, they don’t throw the egg out. Until recently, the ornithologists’ theory was: the “victims” have yet to learn to counteract. Turns out: they may even profit from having strangers’ chicks in their nest! So is cuckoo’s behavior a phenomenal trick or an evolutionary riddle?