Cuckoos

June 7, 2019

Black-billed Cuckoo
Coccyzus erythropthalmus

Yellow-billed Cuckoo
Coccyzus americanus

by Helena Ives

Working as a naturalist at a State Park gets me a lot of questions. It also lets me spend the bulk of my time out in nature (I know, I’m very lucky), to experience it firsthand so I can do a better job of leading and teaching others. It’s been through answering (and asking) questions and spending time in nature that I’ve expanded my birding skills in a dramatic way over this migratory season. I’ll admit that last year I struggled with most birds that were outside of the group of shorebirds I worked with every day. I’ve been shocked to see how quickly I was able to learn to identify songbirds at the forested state park where I work by spending just 15-30 minutes practicing it every day.

It was on a recent bird walk I was leading that my group stumbled upon one of those new birds for me to ID – our first cuckoo of the season in a less-traveled portion of Goodwin State Forest, near one of the park’s three wetlands. Though we never got to lay eyes on the conspicuous Yellow-billed Cuckoo that we heard, its distinctive, guttural-sounding call was enough to confirm the ID and welcome them back to our forest.

Black-billed Cuckoo, by Patrick Comins.

As neotropical-migrants, both the Yellow-billed and Black-billed Cuckoos spend late April to late September within their breeding territory, which typically spans north and east from Mexico and South America. The Yellow-billed Cuckoo is generally more common and widespread, with a breeding range that extends from the northern edge of Mexico, east from the western borders of Texas through Minnesota, and north through the northern borders of New England and New York. The Black-billed Cuckoo’s breeding range extends further west, to Montana, but has a southern boundary from Kansas to Maryland.

Regardless, both of the Cuckoo species breed in Connecticut and fill our woods and the edges of freshwater wetlands with their emphatic calls, described as 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.

[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 cuckoo species 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.

Yellow-billed Cuckoo. Note that this bird is missing its tail. Photo by Patrick Comins.

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.

Interestingly, both cuckoo species 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 the nest. 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, due to a number of human-imposed threats.

Pesticide ingestion in both species has been found to be incredibly high, because of frequent ingestion of caterpillars. Both species are dependent, during breeding and migration, on insect populations. It has been found that their entire reproductive cycle will be delayed or stopped if enough insects are not present, which also leaves them dependent on a number of other habitat features that impact insect populations. Consequently, population fluctuations have been found to correlate with inclines or declines in caterpillar, or other insect, populations.

Both cuckoos prefer dense, large sections of forest and a dense, shrubby understory, and 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, depending on the current population and the subspecies classification status, as have individual states and Canadian provinces. Overall, their population ranges have declined over the years 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. Previously, she worked for Connecticut Audubon monitoring birds as part of the Audubon Alliance for Coastal Waterbirds.