Earlier this week, I was researching and writing a story for Natural History Magazine about some cuckoos that have taken on the plumage patterns of local hawks and other raptors in order to frighten away other birds from their nests.
“Dressing” like a known predator allows the cuckoos to swoop in and lay their own eggs in the nests, tricking unsuspecting sets of bird-parents into raising the cuckoos’ young. This sometimes happens to comedic effect when you consider how much bigger cuckoos can grow than their host parents.
(By the way, you should read the bio of Thanh-Lan Gluckman, one of the scientists who published the study on cuckoo-raptor plumage; she has taken a fascinating, if self-described “convoluted,” path to evolutionary biology.)
In the course of researching this story, I followed an interesting tangent: In 350 B.C., the ancient Greek philosopher Aristotle made observations in his work “The History of Animals” about both the behavior of cuckoo parents and their striking resemblance to hawks. Stringent scientific studies today support these observations as well as the maxim shared with me by my college ecology professor: Basically, ecology confirms what we already know.
One thing I found amusing about reading these early descriptions was the moral lens through which the cuckoo is viewed for its habits (emphasis is mine):
The cuckoo, as has been said elsewhere, makes no nest, but deposits its eggs in an alien nest, generally in the nest of the ring-dove, or on the ground in the nest of the hypolais or lark, or on a tree in the nest of the green linnet. It lays only one egg and does not hatch it itself, but the mother-bird in whose nest it has deposited it hatches and rears it; and, as they say, this mother bird, when the young cuckoo has grown big, thrusts her own brood out of the nest and lets them perish; others say that this mother-bird kills her own brood and gives them to the alien to devour, despising her own young owing to the beauty of the cuckoo … The cuckoo shows great sagacity in the disposal of its progeny; the fact is, the mother cuckoo is quite conscious of her own cowardice and of the fact that she could never help her young one in an emergency, and so, for the security of the young one, she makes of him a supposititious child in an alien nest. The truth is, this bird is pre-eminent among birds in the way of cowardice; it allows itself to be pecked at by little birds, and flies away from their attacks.
Yes, the cuckoo is full of “cowardice” and is quite aware of it, thank you. On the other hand, the foster-parent bird purportedly “despis[es] her own young owing to the beauty of the cuckoo.” Naturally, they’re going cuckoo for cuckoo chicks!
This tangent took me further down the rabbit hole to the 1891 work of Alfred Russel Wallace, “Darwinism: an exposition of the theory of natural selection.” Wallace makes further reference to how similar several species of cuckoos appear to sparrow-hawks and other “aggressive” birds, despite–or rather because of–the cuckoos’ “exceedingly weak and defenceless” nature.
It’s worth noting that not all cuckoos (the family Cuculidae) exhibit these parasitic adaptations to reproduction. But approximately 41% of them do.