Black-billed Cuckoo by John Sill © Massachusetts Audubon Society. Courtesy of the Museum of American Bird Art.
John Sill is a freelance wildlife artist living in the mountains of North Carolina. He was the illustrator for the Bird Identification Calendar for Mass Audubon for many years. His work has appeared in Birds In Art at the Leigh-Yawkey Woodson Art Museum, Wausau, Wisconsin, and in Art of the Animal Kingdom at the Bennington Center for the Arts in Vermont. He continues to illustrate the "About" and "About Habitats" series of natural history books for children written by his wife Cathryn.
The Black-billed Cuckoo (Coccyzus erythropthalmus) is a generally silent and secretive bird that has an amazing array of biological adaptations for its specialized breeding and feeding ecology. The sexes and juveniles are similar in plumage: drab brown tinged with olive above and light whitish-gray below, with a long tail with dull whitish spots, a dark decurved bill, and a red orbital ring. These characteristics help to distinguish it from its congener, the Yellow-billed Cuckoo (C. americanus), that shows rufous in its primaries, has bold white tail spots, and a yellow lower mandible and orbital ring. The Black-billed Cuckoo shows no geographic variation in size or plumage and thus has no recognized subspecies. It is more closely related to the South American Gray-capped Cuckoo (C. lansbergi) than to the Yellow-billed Cuckoo with whose range it overlaps.
Black-billed Cuckoos breed from Alberta eastward across southern Canada to Nova Scotia and in the United States from Wyoming and Montana east through New England and south to Virginia, and farther south in the Appalachians. The breeding range covers more than one-third of the United States. In Massachusetts, it is an uncommon breeder, but may periodically be considerably more common in years when gypsy moth, tent caterpillar, or other caterpillar infestations occur. Black-billed Cuckoos are long-distance nocturnal migrants, wintering in South America as far south as Bolivia, but their cryptic plumage and behavior leaves their migration paths and winter distribution poorly known. In Massachusetts, they are considered uncommon to sometimes fairly common migrants. They tend to be late migrants, often not arriving until late May or early June. After their arrival, they appear to be somewhat nomadic, apparently searching for caterpillar infestations once they are on their breeding grounds. In fall, they migrate south from late August to occasionally as late as early October.
The breeding biology of Black-billed Cuckoos is not well known, but they are probably monogamous and single brooded. The most common call, given by both males and females, is a repetitive, somewhat liquid cu-cu-cu-cu, accompanied by tail pumping. They call most often during pair formation and nest building and regularly call at night during the breeding season. They also give a variety of calls and choking sounds during courtship and in alarm situations. Little is known about pair formation or nest building in this secretive species.
Black-billed Cuckoos prefer deciduous or deciduous-coniferous forests or woodland edges, often with water and scattered thickets nearby. In Massachusetts, they are particularly common breeders in the scrub oak forests and woodlands of Cape Cod and the Islands. Both parents may construct the usually flimsy nest, which is generally well concealed by foliage, three to six feet from the ground in forking branches. Nests are flimsy, shallow cups made of twigs and lined with leaves, pine needles, plant fibers, down, moss, or other fine materials. Sometimes, Black-billed Cuckoos are intraspecific brood parasites, laying their eggs in other Black-billed Cuckoo nests. They occasionally lay eggs in the nests of other species such as American Robins, Gray Catbirds, or Northern Cardinals. This brood parasitism is apparently a response to abundant food as typified by extensive caterpillar infestations. The Black-billed Cuckoo egg color of blue green may be an example of egg mimicry as most of the species they parasitize lay blue green eggs.
In normal nesting situations, both parents develop brood patches, and both parents incubate the usual clutch of three to six eggs for the 10–11 days until hatching. The chicks are altricial, being nearly naked with eyes closed at hatching. Both parents feed the chicks crushed rather than regurgitated food. The young fledge in about a week, although they can't fly for another three weeks. This rapid growth is perhaps an adaptation to interspecific brood parasitism, when the young have to outgrow their foster siblings. The parents will defend the nest with aggressive postures, shoulders humped, tail fanned, and wings spread. They will sometimes even fly at intruders with bill open and tail spread while giving alarm calls. Chicks respond to intruders by remaining motionless with an erect posture, outstretched neck, and bill pointed to the sky, bittern-like.
Black-billed Cuckoos, when feeding on caterpillars or katydids, usually remain stationary until they sight their prey, then hop or run to glean prey from the branch or foliage. They may hover-glean foliage as well. They regularly rip open the tents of tent caterpillars, and sometimes even feed on the ground. They take mostly large prey such as caterpillars, crickets, grasshoppers, and butterflies. They also occasionally eat bird eggs and sometimes fruit in summer. Black-billed Cuckoos are versatile in their food preferences and will exploit almost any local concentrated prey. An interesting adaptation to extensive foraging on hairy caterpillars whose spines puncture the cuckoo's stomach lining and may obstruct digestion, is to slough off the stomach lining—spines and all—and periodically regurgitate it as a pellet.
Black-billed Cuckoo populations have generally declined, especially in the 1980s and 1990s, partially as the result of pesticide poisoning and reduced caterpillar availability due to extensive spraying. Predation is poorly known, but Black-billed Cuckoos are probably subject to the usual mammalian and avian predators, and many are killed in collisions with structures during migration. Their skulking behavior and dull plumage, however, probably help to reduce predation. Population trends are hard to follow because Black-billed Cuckoos are at least partially nomadic in their search for local outbreaks of caterpillars. We can only hope that populations of this secretive species will remain stable.