Growing up Cuckoo: far from being crazy, these unusual birds use every evolutionary strategy to give their offspring--and themselves--the edge.
In fact, cuckoos belong to a large order of birds (Cuculiformes) with close to 180 species worldwide, including the roadrunner of cartoon fame. Most are elusive and retiring, more commonly heard than seen. Eastern Canada is host to two cuckoo species, the yellow-billed cuckoo and the black-billed cuckoo, which can sometimes be spotted in rural backyards, urban ravines, or parks. Superficially the birds are similar in appearance and song and are found in similar habitat--they prefer woodland edges and rural landscapes.
How the name cuckoo originated is unambiguous. It is an onomatopoeic word describing the call of the male common cuckoo, a widespread summer resident of Europe and Asia. The song seems to have struck a chord with linguists in various countries and throughout the ages. During Saxon times, the name was spelled kokila, and in Old and Middle English, cuccu, coccou, cukkow, cocow. In France, the name is coucou, in Germany kuckuck, and in Greece kokkus.
If people had been fair to the cuckoo, the colloquial name-calling would have stopped with this imitation of its song. But the common cuckoo shows great persistence in vocalizing its very recognizable call and will often repeat the song, rather monotonously, hundreds of times in succession. This vocal tic led unfairly, though perhaps understandably, to the other definition of the word, suggesting eccentricity and craziness.
Sadly, maligning of this bird's character does not stop there. The colloquialism "cuckolded" is the one that cuckoo aficionados object to most vehemently. A cuckold is defined as a man whose wife is unfaithful. But why fault the cuckoo for such an unfortunate circumstance? While cuckoos do exhibit some rather bizarre reproductive strategies, cuckoldry has not been reported among cuckoos--at least not in Canada.
But several members of the cuckoo family do practice the strategy of brood parasitism--one of the most interesting aspects of cuckoo biology. A cuckoo will lay its eggs in the nest of another species, leaving the host species with the responsibility of incubating the eggs and caring for the offspring. In human terms, this would be akin to leaving the kids with the neighbours and then moving out of town. The North American brown-headed cowbird, which is not a cuckoo but a member of the blackbird family, and the common cuckoo mentioned earlier are probably the world's most successful and well-known brood parasites. But the yellow-billed cuckoo and black-billed cuckoo are not above resorting to this behaviour.
Typically, these Canadian cuckoos build flimsy nests of twigs and grasses in a small bush or tree, where they incubate their eggs and raise their young. But occasionally, for reasons that are not known, they choose to lay their eggs in other birds' nests. They favour other cuckoos or species that have similar coloured eggs to their own, such as the American robin and other thrushes.
The similarity in egg colour presumably offers a greater chance that the host species will not realize the deception.
Once the egg has been accepted by the host bird, cuckoos have a few more adaptations working in their favour. First is a short incubation period of just 11 to 12 days, which allows their eggs to hatch before those of the host bird. Second is the remarkably fast growth of the nestling. While birds of similar size, such as robins, fledge from the nest in about 13 days, cuckoo young are ready to leave in about 7. They hatch from the egg blind and almost naked, but within two hours are able to lift their heads above the rim of the nest. They quickly begin begging for food, and even have small "sucking pads" in their mouths that may help them grasp it.
On the second day, they open their eyes and quickly become more agile. By the seventh day feather sheaths burst simultaneously--the young bird becomes fully feathered in about two hours. By the end of that day they are able to leave the nest, walking along nearby branches. Becoming mobile early gives them a little extra protection from predators and more attention from the host parents.
Cuckoos, it seems, are not as crazy as they sound.
Mark Peck is a technician in the ornithology section of the ROM's Department of Natural History.