by Nicolette L. Cagle, August 14, 2026
In the last post, we followed the cuckoo family through deep time, from the early Cenozoic fossil record to the remarkable diversity of modern cuckoos. We also noted that the modern Cuckoo family extends beyond the notorious brood parasite, the Common Cuckoo, and embraces roadrunners, coucals, anis, koels, ground-cuckoos, and many species that build nests and raise their own young.
In this post, we narrow our view to two quiet North American relatives: the Black-billed Cuckoo (Coccyzus erythropthalmus) and the Yellow-billed Cuckoo (Coccyzus americanus). These two species look similar, overlap across much of eastern North America, and straddle the evolutionary border between ordinary parental care and occasional brood parasitism. Remarkably, both these species organize their lives around ecological pulses, such as monsoon greening, caterpillar outbreaks, and the emergence of periodical cicadas. To understand their sense of place, we have to ask not only where they live, but when resources arrive.
Physically, the two North American cuckoo species are variations on one long-tailed, brown-backed theme. The Black-billed Cuckoo has the cleaner dark bill, a red eye-ring as an adult, muted gray beneath the tail, and little rufous in the wing. The Yellow-billed Cuckoo has yellow along the lower mandible, bold white tail spots, and a cinnamon flash in the primaries.
Ecologically they overlap, but they are not interchangeable. Northern Illinois surveys associated Black-billed Cuckoos with more open, shrubby, early-successional conditions, while Yellow-billed Cuckoos favored older succession and greater forest cover (Johnson & Benson, 2022, 2024). The Black-billed Cuckoo often works lower vegetation and sometimes the ground, while the Yellow-billed Cuckoo more often searches the middle and upper foliage. In the same woods, they may inhabit different vertical and successional versions of place.
Black-billed and Yellow-billed Cuckoos live in two worlds at once, existing both in the world of an ordinary nest-building bird and the parasitic world of some of their relatives. In their parental lives, both Black-billed and Yellow-billed Cuckoos mostly lay eggs in their own nests and raise their own young. They migrate in spring and fall like warblers and vireos, and they glean branches and leaves for insect prey. Yet they also possess a constellation of traits that makes the family resemblance to brood parasites clear, including short incubation, asynchronous and sometimes irregular laying, variable clutch size, occasional parasitism of another cuckoo’s nest, and a readiness to wander after food pulses (Dearborn et al., 2009; Fleischer et al., 1985; Nolan & Thompson, 1975).
That being said, the tendency toward brood parasitism for these species is relatively weak. While in one study, protein evidence demonstrated that more than one female contributed eggs to a Yellow-billed Cuckoo clutch (i.e., intraspecific brood parasitism) (Fleischer et al., 1985), a later search of 10,197 songbird nests found no Coccyzus eggs at all. This research suggests that reports of cuckoos parasitizing songbirds may represent mistaken attempts to lay in another cuckoo’s nest rather than a regular strategy of exploiting smaller hosts (Dearborn et al., 2009).
Between Continents. Like retired “snowbirds” bouncing between New York and Florida, Black-billed Cuckoos spend the summer across the northern half of the eastern and central United States and southern Canada. They pass through the southeastern United States, Mexico, and Central America during fall migration, then become far more difficult to trace. Their best-established nonbreeding range lies in northwestern South America (especially Colombia, Ecuador, Peru, Bolivia, and western Brazil) with a broader, poorly known zone of “wandering” into Paraguay, Argentina, and southeastern Brazil. The reason behind the range extent mystery is partly behavioral since the species is quiet on breeding nonbreeding grounds, easy to miss, and visually similar to other Coccyzus cuckoos (Schunck et al., 2024).
Recent Brazilian records show what wandering looks like. In 2023, one juvenile female died after striking a window near São Paulo on January 8; its stomach held a saturniid caterpillar. An adult appeared at the edge of an urban forest fragment in Rio de Janeiro on November 4. A very worn juvenile was mist-netted on November 25 in coastal restinga—a landscape of dunes, dense shrubs, and temporary lagoons—in Santa Catarina. These joined a historical Atlantic Forest observation from Paraná in 1999 (Schunck et al., 2024).
Schunck and colleagues (2024) noticed that the Atlantic Forest records coincided with strong El Niño years and proposed that altered rainfall and atmospheric circulation might push some cuckoos farther east in South America in El Niño years. A second possibility is that the birds may regularly use portions of the Atlantic Forest but remain hidden there, mistaken for other cuckoos or simply unheard. The difference between a true range expansion and a range that simply poorly perceived and recorded by people is one of the enduring problems of studying quiet, brown birds (Schunck et al., 2024).
In fact, no matter the season or country, Black-billed Cuckoos are secretive. Long described the species as preferring “the darkest, dampest parts” of timbered country in Kansas (Long, 1935). In Louisiana, a nest sat only 1.3 meters high in a roadside tangle of blackberry, saplings, and vines beside second-growth forest (Graves et al., 2001). In Brazil, the birds have occurred along secondary-forest edges, near water, in urban fragments, and among coastal shrubs (Schunck et al., 2024). The common thread is dense cover.
Still, given its cryptic nature, the Black-billed Cuckoo would rather be heard than seen, but only when breeding. On breeding grounds it gives repeated coos, low croaks, and rattling calls, sometimes through the night. Researchers capitalize on that responsiveness. For example, in Illinois, broadcasting cuckoo calls increased the probability of detecting an individual about twelvefold for Black-billed and sixfold for Yellow-billed Cuckoos (Johnson & Benson, 2022). In Montana, however, passive acoustic recorders paired with a machine-learning classifier achieved higher detection at lower projected cost than in-person playback surveys. This means that playback can elicit a response during a short visit, while autonomous recorders can keep listening after the humans leave (Kurtin et al., 2025).
This combo of acoustic detection methods can also expose how temporary a cuckoo’s residence can be. For instance, Johnson and Benson (2022) estimated average among-site emigration probabilities of 86% for Black-billed and 47% for Yellow-billed Cuckoos during the breeding season. In this case, “occupied” doesn’t mean settled for the summer. For cuckoos, a map of habitat occupancy is never only a map of trees, it’s a more complicated map of shifting food supplies.
Follow the Food. Migration ecologists use the term “green wave” as shorthand for the seasonal surges of newly leafed, highly productive vegetation that moves across a continent. Many avian migrants ride that wave northward in spring and then stay put on their breeding grounds. North American cuckoos add nuance to that story.
In particular, Yellow-billed Cuckoos in the arid Southwest show a species following not spring itself but a later, rain-driven pulse of green. In Arizona, satellite-derived measures showed that Yellow-billed Cuckoos selected riparian landscapes whose vegetation reached peak greenness about 29 days later than average, was 36% more seasonally dynamic, and was slightly more productive. Those “later-greener-dynamic” sites responded to the North American monsoon, a seasonal shift to more southerly winds that bring moisture-laden air from the Pacific Ocean and the Gulf of Mexico to the southwestern United States. The pattern supports a two-step interpretation: cuckoos move with monsoon-driven greening at a broad scale, then choose nesting neighborhoods that optimize near-term foraging conditions (Wallace et al., 2013). The green wave here is not a smooth latitude line exhibited by other migratory birds. Instead, it’s a surge of life after rain in a desert.
The Black-billed Cuckoo may follow an even more discontinuous wave, a wave of caterpillars erupting in patches. Tent caterpillars, fall webworms, and spongy moth larvae do not increase evenly across a forest. Their outbreaks are patchy and temporary. A cuckoo arriving from South America appears to inspect a large landscape, abandon poor resource patches, and settle where caterpillars are abundant This helps explain the paradox of a bird that migrates on a continental schedule, while also being nomadic once it is supposed to have “arrived”.
Cuckoos and caterpillars have a close relationship. While most birds avoid heavily setose caterpillars or spend a lot time stripping them of their bristles, cuckoos have a different strategy. They may beat a caterpillar against a branch, but they also possess an internal accommodation. When caterpillar hairs and spines lodge in the cuckoo’s soft gizzard lining, the lining itself is sloughed and expelled as a pellet. Individual stomachs have contained more than one hundred caterpillars, and a Yellow-billed Cuckoo can consume roughly one hundred in a single sitting (Cornell Lab of Ornithology, n.d.-a, n.d.-b).
This North American cuckoo adaptation explains why a caterpillar outbreak shift the Black-billed and Yellow-billed Cuckoo distribution map almost immediately. During spongy moth outbreaks in the eastern United States, both Black-billed and Yellow-billed Cuckoos rise above their long-term averages on Breeding Bird Survey routes within the outbreak zone, while remaining average or below average before and after the outbreak and on nearby nonoutbreak routes (Barber et al., 2008). An Ontario-based master’s thesis, drawing on more than fifty years of bird counts and forest tent caterpillar defoliation, found a large local signal. At complete defoliation, median Black-billed Cuckoo counts rose to roughly eight times their baseline in the Boreal region and by more than 200% in the Hardwood Transition region. At the same time regional, time-lagged estimates were positive but much less certain, with broad intervals overlapping zero (Belmar Lucero, 2020), suggesting that local concentrations of cuckoos can be quite high even if population growth in a particular region remains equivocal.
That being said, food may also shift the reproductive cuckoo clock. A short historical report linked dense forest tent caterpillar prey with earlier laying and larger Black-billed Cuckoo clutches (Sealy, 1978). The observation is consistent with a bird converting a caloric windfall into eggs. Thus, a pulse in caterpillars can attract breeders, accelerate laying, or enlarge a clutch, but it can be challenging to distinguish movement in response to food from resource-driven reproduction.
Yellow-billed Cuckoos are also famously caterpillar-hungry, but they can provision young with a broader prey portfolio. At thirty California nests, observers identified 2,420 prey deliveries: 44.9% green caterpillars, mostly sphinx moth larvae; 23.8% tree frogs; 21.8% katydids; 8.7% grasshoppers; and a remaining sliver of cicadas, dragonflies, beetles, spiders, and other prey. Egg production rose with the proportion of katydids and fell as the proportion of green caterpillars increased, while shorter prey-capture times were associated with more fledglings (Laymon, 1998). This suggests that prey abundance alone is not equivalent to nutritional value or the resources needed to make an egg.
In unusually rich years, some Yellow-billed Cuckoo pairs in that study produced two broods, and in one of twelve years a few produced three, raising as many as ten young. Double brooding still occurred in fewer than half the study years, but triple brooding was exceptional (Laymon, 1998). The point is not that cuckoos invariably multiply when insects do, but when resources and timing align, North American cuckoos can capitalize on their fast nesting cycle and turn food pulses into another reproductive attempt.
Speed is the keystone in the bridge between insect pulses and reproductive possibility. In fact, a Yellow-billed Cuckoo can sometimes move from first egg to fledgling in about seventeen days. Incubation lasts roughly nine to eleven days and nestlings may leave six to nine days after hatching. Black-billed Cuckoos are nearly as fast, with roughly ten to eleven days of incubation and six to seven days in the nest. The young depart before they are strong fliers, climbing through branches while their parents continue to feed them (Cornell Lab of Ornithology, n.d.-a, n.d.-b; Graves et al., 2001). That speed also produces odd-looking clutches since incubation can start before laying is complete, with hatchlings often differing dramatically in size.
Periodical cicadas are a different kind of green wave. With cicadas, insect biomass rises from the ground over longer time scales. In an analysis of thirty-seven years of Breeding Bird Survey data and twenty-four potential predator species, fifteen birds changed in abundance around emergence years. Only Black-billed and Yellow-billed Cuckoos were clearly more abundant in cicada emergence years than in the preceding year. Populations sharing the same cicada brood also became synchronized across space (Koenig & Liebhold, 2005), with cuckoos arriving in, or concentrating within, cicada emergence landscapes.
Cicada emergence create cascading ecological changes. During the 2021 Brood X emergence, more than eighty bird species switched at least partly to cicadas. Predation pressure on foliage-eating caterpillars relaxed, which meant that caterpillar density and accumulated oak herbivory approximately doubled (Getman-Pickering et al., 2023). For cuckoos, this is a two-stage opportunity. First, there is an immediate banquet of cicadas. Then there is a secondary release of caterpillars that other birds have temporarily have stopped hunting.
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To close, Black-billed and Yellow-billed Cuckoos do not simply migrate between winter and summer grounds. They move among spatially and temporarily patchy conditions: young thicket and older canopy, drought and monsoon, ordinary insect years and forests suddenly crawling with caterpillars or cicadas. Monsoon-driven green-up can guide a Yellow-billed Cuckoo into a late-peaking desert river corridor. A tent-caterpillar outbreak can pull Black-billed birds into a Canadian forest patch in numbers that seem impossible the following year. A periodical cicada emergence can synchronize cuckoos across a brood’s range and redirect an entire bird community’s appetite (Belmar Lucero, 2020; Getman-Pickering et al., 2023; Koenig & Liebhold, 2005; Wallace et al., 2013).
In the next post, we will follow North American cuckoos out of the forest and into human tradition. We will look at place-specific Ojibwe, Cherokee, and Meskwaki records; listen to the Piedmont fiddle tradition carried by Joe Thompson, Justin Robinson, and Rhiannon Giddens; and trace American cuckoos through poetry and nature writing. These birds that hide in foliage and forests are also tucked away in our music and language.
References
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Belmar Lucero, S. A. (2020). The response of avian predator populations to forest tent caterpillar (Malacosoma disstria; Lepidoptera: Lasiocampidae) outbreaks in Ontario, Canada [Master’s thesis, Lakehead University]. https://thesis.lakeheadu.ca/bitstreams/bbc1ca89-beea-4a24-9478-0246cc04c580/download
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