Black-billed Cuckoo

The Black-billed Cuckoo is a slender, long-tailed bird closely related to the Yellow-billed Cuckoo, sharing the same smooth grayish-brown upperparts and clean white underparts. As its name suggests, its entire bill is dark, lacking the yellow lower mandible of its cousin, and it shows a narrow but noticeable red ring around the eye.

Like other cuckoos, it is a quiet, unobtrusive bird that spends much of its time hidden in dense foliage, more often heard than seen. Its populations track outbreaks of tent caterpillars and other irruptive insect prey, so numbers can fluctuate noticeably from year to year in a given area.

Key Field Marks

• Slim, long-tailed shape with grayish-brown upperparts and white underparts
• Entirely dark, blackish bill
• Distinct red eye-ring
• Tail spotted below with small, grayish-white dots, less bold than the Yellow-billed Cuckoo's
• No rufous patch in the wing

Similar Species

The Yellow-billed Cuckoo shares the same overall shape but shows a yellow lower bill, a rufous wing patch visible in flight, and larger, bolder white tail spots. The Black-billed Cuckoo's plainer wings and red eye-ring are the most reliable distinctions at close range.

Black-billed Cuckoos breed across the northeastern and north-central United States and southern Canada, favoring dense shrubby thickets, overgrown fields, forest edges, and riparian tangles, often at slightly cooler and more northerly locations than the Yellow-billed Cuckoo. They are long-distance migrants that winter in South America, primarily in the Amazon basin region.

Because their movements and breeding effort are closely tied to caterpillar outbreaks, Black-billed Cuckoos can appear abundant in some years and scarce in others within the same patch of habitat.

Like the Yellow-billed Cuckoo, this species specializes in eating large, hairy caterpillars that many other birds reject, along with other sizable insects. It moves deliberately through dense cover, often staying motionless for long periods, which combined with its quiet habits makes it one of the more challenging eastern birds to actually observe.

The song is a rhythmic, evenly-paced series of hollow "cu-cu-cu" notes, distinctly different from the slowing, descending call of the Yellow-billed Cuckoo. Nests are flimsy stick platforms hidden in dense shrubs or low trees, and — like its relative — the species can have an unusually short incubation period, an adaptation likely linked to unpredictable caterpillar food booms.