Daily Bird: Cuckoos

Yellow-billed Cuckoo. Photo by Sharon Cuartero.

June 15, 2020

Black-billed Cuckoo
Coccyzus erythropthalmus

Yellow-billed Cuckoo
Coccyzus americanus

Revised from a version published in June 2019.

by Helena Ives

Both the Yellow-billed Cuckoo and Black-billed Cuckoo breed in Connecticut and fill our woods and the edges of freshwater wetlands with their emphatic calls — ka-ka-ka-ka-ka-kow-kow-kowlp-kowlp-kowlp-kowlp for the Yellow-billed and cu-cu-cu-cu, cu-cu-cu-cu, cu-cu-cu-cu for the Black-billed.

The Yellow-billed Cuckoo is generally more common in Connecticut, which you can see on the eBird maps for June 2020: Yellow-billed here and Black-billed here.

Listen to the songs: Black-billed here; Yellow-billed here. You can also hear the classic song of the Common Cuckoo, Cuculus canorus, here.

If you’re lucky enough to see them, the cuckoos we have here look similar to each other, except for the bill and the underside of the long tail feathers.

As you would probably guess, the Yellow-billed Cuckoo has a yellow bill, but only the lower mandible – the lower portion of the bill – is yellow; the Black-billed Cuckoo has an entirely black bill. In both species the bill is thick, with a hooked tip, which aids in foraging for insects, caterpillars, crickets, and cicadas in particular.

The Yellow-billed has white spotting on the underside of its tail feathers compared to the Black-billed, which has tail feathers that are white with pale fringing near the end. Both cuckoos are robin-sized, with a drab grayish-brown on the upper portion of their heads and bodies, and white underparts.

Black-billed Cuckoo. Photo by Patrick Comins.

Interestingly, both cuckoos have a really rapid breeding and chick-development cycle. From the days the eggs are laid, it typically only takes three weeks for chicks to hatch and fledge. All hatchings have “bursting feather sheaths,” which allow them to become fully feathered within two hours of the onset of the process.

Yellow-billed and Black-billed Cuckoos are parasitic breeders – they lay their eggs in the nests of other species. But unlike Brown-Headed Cowbirds, they don’t always do this, and when they do it’ll likely be in the nest of an American Robin, Gray Catbird, or Wood Thrush.

Current population trends for both Yellow-billed and Black-billed Cuckoos are downward, because of a number of human-imposed threats.

Both species eat almost nothing but insects, and their reproductive cycle will be delayed or stopped if there aren’t enough insects to eat. Pesticide concentrations have been found to be incredibly high in cuckoos, because they eat so many caterpillars — spongy moths, for example — that are targeted by spraying. Population fluctuations have been found to correlate with increases or decreases in insect populations.

Both cuckoos prefer dense, large sections of forest and a dense, shrubby understory. Both have been found to be heavily impacted by habitat fragmentation and development. Especially in the northeast, cuckoos have even been found to move out of habitats that have high levels of vehicular traffic because automobile noise makes it harder for cuckoos to hear other cuckoos calling.

The U.S. Fish and Wildlife Service has considered both species for various threatened statuses over the years, as have individual states and Canadian provinces. Overall, their population ranges have declined and formerly included states and provinces further west than where they extend to now. Declines are expected to continue in the absence of habitat and conservation management.

A graduate of the University of Connecticut with a degree in wildlife conservation, Helena Ives is a naturalist for the Connecticut DEEP at the Goodwin State Forest and Education Center in Hampton.