On a still, late summer night, a soft, deep, rapidly repeated “co-co-co-co” sometimes betrays the presence of one of Canada’s most surreptitious birds. By day, the mysterious black-billed cuckoo—about the size of a blue jay, but much sleeker—keeps silently out of sight. When it’s not hunched stalk still, it’s slinking slowly through dense, tangled forest edges and understory, or shrub thickets and thorn trees.
Cuckoos are connoisseurs of caterpillars that are too hairy, too spiny, or too toxic for most other birds. Ingested bristles stick into the long-tailed bird’s soft, regenerative gizzard lining, eventually coating the lining like fur until it detaches and the cuckoo coughs up the whole mass as a pellet.
Returning late in the spring from South America, cuckoos wander across Canada, east of the Rockies, for up to hundreds of kilometres in search of heavy caterpillar infestations. They usually nest in June and July, but sometimes hold off until finding enough to eat later in the summer. When congregating at outbreaks of tent caterpillars, fall webworms, or spongy moths, the birds can be relatively common, but they may move on the next year if the little munchers have subsided.
FAQ: Spongy moth caterpillars
The look-alike mates nest more quickly than any other similar-sized birds. After throwing together a flimsy platform of sticks—usually a metre or two off the ground—most lay two or three greenish-blue eggs, which hatch in 10 to 11 days. The jet black hatchlings can climb within hours and sprout feathers and leave the nest when six or seven days old. Under parental care, they clamber with agility through trees spread across hundreds of metres until they can fly a couple of weeks later.
During caterpillar outbreaks, females may lay extra eggs, occasionally in the nests of other birds. If they don’t reject the eggs, the foster parents feed the resulting chicks as their own.
This article was originally published in the August 2024 issue of Cottage Life.
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