General Biology

The order Cuculiformes comprises small- to medium-sized birds, with a worldwide distribution in forests and woodlands of temperate, subtropical, and tropical climates. Most are arboreal, although some are ground dwelling. They range in length from 16 to 70 centimeters (cm) and in weight from 17 grams (g) (little bronze cuckoo, Chrysococcyx minutillus) to 770 g (buff-headed coucal, Centropus milo).³¹ Globally, most Cuculiformes populations are stable; however, 18 species are classified as vulnerable, near threatened, or endangered by the International Union on the Conservation of Nature (IUCN).¹⁹

Historically, this order used to include three families: (1) the Cuculidae, (2) the Musophagidae (turacos, plantain eaters, and go-away birds), and (3) the Opisthocomidae (hoatzin); however, most taxonomists have elevated the last two families to separate orders. The Cuculidae family is currently divided into five subfamilies comprising 32 genera; the brood parasitic cuckoos and malkohas (Cuculinae, 88 species), the couas and Old World ground cuckoos (Couinae, 13 species), the coucals (Centropodinae, 26 species), the anis and Guira cuckoos (Crotophaginae, 4 species), and the New World ground cuckoos (Neomorphinae, 10 species).^13,31

Although most cuckoos are diurnal, they are often highly secretive, with many species vocalizing only at night. Their vocalizations are species specific and are often used to identify cryptic species. Sexual dimorphism occurs in some species, with females being larger than males in 71% of the species with parenteral care, while males are larger in 84% of the brood parasitic species. Almost all parenteral species (95%) are monomorphic, on the basis of their plumage, whereas 41% of the Old World brood parasitic species and malkohas are dimorphic.^25,31 In monomorphic species, gender determination may be accomplished through deoxyribonucleic acid (DNA) analysis of whole blood or blood feathers or via laparascopy.³⁴

Unique Anatomy

Zygodactyly is one of the most distinctive features of cuckoos. The body forms of the Cuculidae vary, depending on their lifestyle, with arboreal cuckoos having long tails and slender bodies and terrestrial cuckoos being heavy bodied and proportionately longer tarsi. Well-developed eyelash feathers are a characteristic feature of cuckoos. The bill has no cere, is usually slender, and is slightly arched. The tarsi are often unfeathered and scutellate. The uropygial gland is prominent. Depending on the species, the wing has 10 primary and 9 to 13 secondary remiges, and usually 10 retrices exist, with only 8 in the anis and the Guira cuckoo. During molting of the wing feathers, the odd numbered primaries are shed and regrow first followed by the even numbered primaries, a pattern that is unique to cuckoos. The young of several cuckoo species may be distinguished by the unique pattern of white to yellowish-tan papillate patches in the oropharyngeal cavity.^7,31

Special Housing Requirements

The Cuculidae are not commonly found in zoologic collections, although globally several members of the cuckoo family are represented in institutions, including several species of cuckoo (Guira, fan-tailed, hawk, channel-billed, squirrel, and Renault’s ground cuckoos), malkohas, yellow bill coul, coua, coucal, and roadrunners.²⁰

Appropriate exhibits, coupled with suitable social groupings and opportunities to express species-appropriate behaviors, are important to maximize the physical and mental well-being of these birds. For arboreal species, large meshed exhibits with appropriate perching and plantings that allow for uninterrupted flight are most ideal, and terrestrial species may be housed in planted exhibits with natural substrates. Feather clipping may be performed to keep the birds in open exhibits. In general, cuckoos are not tolerant of cold environmental temperatures (less than 5° C or 40° F), so additional heat sources should be provided when the birds are housed outdoors in temperate climates. Some species of anis may adapt to cooler climates by lowering their body temperature at night (nocturnal torpor) and will demonstrate sunning behaviors to increase their body temperature.¹

Most species of cuckoos are not housed in mixed species exhibits because of their aggressive nature, as they will prey on smaller birds or their eggs and offspring.^24,31 A few species are amenable to being housed with other birds; for example, roadrunners have been displayed successfully with burrowing owls. Intraspecific aggression may also be an issue, as most cuckoos are solitary in nature. A notable exception is the Guira cuckoo, which is a social species with communal nesting activities and postnatal group affiliations.^1,27,31

Free-ranging cuckoos are carnivorous, with most being insectivorous, preying on noxious insects such as caterpillars that are often avoided by other birds. They remove the indigestible and toxic leaf products within the intestines of the caterpillars by beating them or wiping them back and forth on branches or by passing them back and forth through their bills before ingesting them. The hairs on the caterpillars are indigestible as well and form a mat within the ventriculus, and the mat is later egested as a pellet. Other prey items, depending on the cuckoo species, include locusts, grasshoppers, millipedes, centipedes, spiders, phalangids, terrestrial snails, tree frogs, lizards, snakes, and mice. Brood parasitic species often take eggs from the nest of their host, whereas coucals and roadrunners consume nestling birds. The diet of a few of the Old World species such as cous, some malkohas and coucals, channel-billed cuckoo, dwarf koel, and common koel consists mainly of fruits (figs, tamarinds, berries, and palm oil fruits) with occasional insects. During the breeding season, roadrunners feed predominately on snakes and lizards, often beating their prey repeatedly against a rock.^1,31,36

Restraint and Handling

Care should be taken when handling and restraining cuckoos, especially the smaller species, to prevent injury to the bird. Physical restraint and anesthetic techniques are similar to those used for other similar-sized avian species. Induction and maintenance with gaseous anesthetics (isoflurane or sevoflurane) in oxygen at appropriate flow rates is most commonly used for anesthesia. Intubation is straightforward. During recovery from anesthesia, birds should be confined in a quiet holding cage, until they are capable of standing, to prevent injury.