Is there a scene more horrifying than the baby cuckoo alone in a nest: the waxy skin, the eyeballs covered in the skull, the sunken back – evolved to help it scoop the other eggs over the edge and on to the ground. Nobody has taught the baby how to eliminate its adoptive siblings. The cuckoo hatches with this instinct driving it: a natural born “obligate brood parasite”.
When a common European cuckoo has successfully laid her egg in a reed warbler’s nest, she “gives a chuckle call, as if in triumph”: the call sounds like a sparrowhawk, a predator, which distracts the host. “The female cuckoo enhances her success by manipulating a fundamental trade-off in host defences between clutch and self-protection,” the authors who discovered this wrote, in a paper titled Female cuckoo calls misdirect host defences towards the wrong enemy. In one summer, a female cuckoo can lay 25 malevolent eggs.
