Black-billed Cuckoo
Coccyzus erythropthalmus
Adults have a long, graduated brown tail and a black, slightly downcurved bill. The head and upper parts are brown and the underparts are white. The feet are zygodactylous. Juveniles are drabber and may contain some rufous coloration on the wing. The adults have a narrow, red orbital ring while the juveniles' is yellow. Black-billed cuckoo chicks have white, sparsely distributed, sheath-like down that contrasts heavily with their black skin. Voice: When they are a couple of days old, the chicks can make a buzzing sound that resembles an insect and a few days later, they can make a low barking call when disturbed. The call of this species is 2–5 sets of "coo" notes that are high-pitched, rapid, and repetitive. There is a slight pause between each set. The phonetics are often written "coo-coo-coo-coo, coo-coo-coo-coo, coo-coo-coo-coo, ...".
ID text from Wikipedia, CC BY-SA 4.0

Dark-billed Cuckoo
Coccyzus melacoryphus
The dark-billed cuckoo is 25 to 28 cm (9.8 to 11.0 in) long, about half of which is the tail. Males weigh about 42 to 54 g (1.5 to 1.9 oz) and females about 50 to 66 g (1.8 to 2.3 oz). Males and females have the same plumage. They have a gray crown and nape and grayish brown upperparts. Their wings are a darker grayish brown with no rufous. The upper surface of their tail is brown; the underside of the central pair of feathers is brown with black tips, the next pair blackish with narrow white tips, and the rest black with wide white tips. Voice: The dark-billed cuckoo's song is variously described as "six to eight resonant, buzzy kazoo-like notes" and "a ventriloquial ga-ga-ga-go-go." Another vocalization is "a descending series of guttural notes" that may also be a song. It makes "a dry-sounding buzz...dddddrr" call.
ID text from Wikipedia, CC BY-SA 4.0
Where you might meet both
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Play today's Daily BirdPhotos and recordings are credited to their authors under the licence shown. Full profiles: Black-billed Cuckoo and Dark-billed Cuckoo.