structural:summarization
Behaviour and ecology

The cuckoos are, for the most part, solitary birds that seldom occur in pairs or groups. The biggest exception to this are the anis of the Americas, which have evolved cooperative breeding and other social behaviours. For the most part, the cuckoos are also diurnal as opposed to nocturnal, but many species call at night (see below). The cuckoos are also generally a shy and retiring family, more often heard than seen. The exception to this is again the anis, which are often extremely trusting towards humans and other species.

Most cuckoos are insectivorous, and in particular are specialised in eating larger insects and caterpillars, including noxious, hairy types avoided by other birds. They are unusual among birds in processing their prey prior to swallowing, rubbing it back and forth on hard objects such as branches and then crushing it with special bony plates in the back of the mouth. They also take a wide range of other insects and animal prey. The lizard cuckoos of the Caribbean have, in the relative absence of birds of prey, specialised in taking lizards. Larger, ground types, such as coucals and roadrunners, also feed variously on snakes, lizards, small rodents, and other birds, which they bludgeon with their strong bills. Ground species may employ different techniques to catch prey. A study of two coua species in Madagascar found that Coquerel's coua obtained prey by walking and gleaning on the forest floor, whereas the red-capped coua ran and pounced on prey. Both species also showed seasonal flexibility in prey and foraging techniques.

The parasitic cuckoos are generally not recorded as participating in mixed-species feeding flocks, although some studies in eastern Australia found several species participated in the nonbreeding season, but were mobbed and unable to do so in the breeding season. Ground cuckoos of the genus Neomorphus are sometimes seen feeding in association with army ant swarms, although they are not obligate ant followers, as are some antbirds. The anis are ground feeders that follow cattle and other large mammals when foraging; in a similar fashion to cattle egrets, they snatch prey flushed by the cattle, so enjoy higher foraging success rates in this way.

Several koels, couas, and the channel-billed cuckoo feed mainly on fruit, but they are not exclusively frugivores. The parasitic koels and channel-billed cuckoo in particular consume mainly fruit when raised by frugivore hosts such as the Australasian figbird and pied currawong. Other species occasionally take fruit, as well. Couas consume fruit in the dry season when prey is harder to find.