CAPRIMULGIFORM

(order Caprimulgiformes), any member of about 100 species of soft-plumaged birds, the major groups of which are called nightjars, nighthawks, potoos, frogmouths, and owlet frogmouths. The order also includes the aberrant oilbird of South America. Most are twilight or night-flying birds. Many produce sounds that are startling, strange, or weirdly beautiful and are surrounded by an aura of mystery richly endowed to elicit interest and sometimes fear from man. The name of the type genus Caprimulgus, goatsucker, derives from an ancient belief that the birds seen flitting about the goats at dusk, actually preying on the insects disturbed or attracted by the goats, were taking milk from the goats' udders, a misconception no doubt fortified by the birds' uncommonly large mouths. There is now a tendency to replace the name goatsucker with the more appropriate term nightjar, derived from the birds' voices. The caprimulgiform birds are sparrow- to raven-sized (1455 centimetres) birds with enormous gapes, cryptically coloured and patterned plumage, short legs and, for the most part, long wings. All caprimulgiform birds are rather similar in general appearance, but each family has certain peculiar characteristics both in form and in habits. Their closest relatives are the owls (Strigiformes), which they resemble in many ways, but there are numerous differences between them. Many of these are internal, but among those externally apparent are the bill and feet, which are not raptorial; the flatter head with eyes placed laterally rather than in a frontal facial disk; the relatively shorter tarsi and longer tails. Closer inspection reveals differences in the number of primary feathers in the wing and usually of secondaries and tail feathers as well. The nightjars also share some features with the swifts (Apodiformes), but these seem to be more superficial and coincidental than indicative of close phylogenetic relationship. Although the true nightjars (Caprimulgidae) are amply distributed throughout the world, the other families are more restricted. The order is absent from New Zealand and some oceanic islands. member of the avian order (Caprimulgiformes) that comprises the soft-plumaged birds known as nightjars, nighthawks, potoos, frogmouths, and owlet frogmouths. It also includes the unique oilbird of South America. The order's closest relatives are the owls (strigiforms), from which caprimulgiforms differ in having the eyes placed laterally on the head and in lacking the raptorial bill and feet. Caprimulgiforms range in size from 5 to 22 inches (14 to 55 cm) in length. Their mouths, a prominent feature, are huge and when open seem to split the head in two. The wings of most species are long and rounded, although they are pointed in some nighthawks (Chordeilinae). During the breeding season some nightjars (Caprimulgidae) grow long tail feathers or white patches on the inner wing, both features being prominent in their aerial courtship displays. In other species the tail is of medium length. The members of this order exhibit some of the most effective cryptic colorations (camouflage) found among the birds. They are all coloured in rust to yellow browns, black, grays, and white. Tree-dwellers like the potoos and frogmouths are streaked like the bark of trees. The woodland-dwelling nightjars, which roost on the ground, are mottled like fallen leaves and other forest detritus. Species that roost on open ground are often patterned differently from the ground itself and look like the stones lying about on the surface. The plumage is soft and fluffy and makes these birds appear much heavier bodied than they actually are. The caprimulgiforms are basically crepuscular (active at dawn and at dusk) and so exploit a niche with little competition from other species. They are mostly insectivorousexcept for the aberrant, frugivorous (fruit-eating) oilbird (Steatornis caripensis)and some of the larger species will take small vertebrates such as frogs or mice. Frogmouths (Podargidae) will also eat fruit. Nightjars and nighthawks generally feed on the wing in savannas and forest clearings. Frogmouths, which prefer woody or forested areas, take most of their prey on the ground, as do the smaller owlet frogmouths (Aegotheles), but the latter will also hunt flying insects from a perch. Oilbirds are nocturnal and live wholly on the fruits of trees such as palms and laurels. The fruit is swallowed whole, and the large hard seeds are regurgitated. These are among the few birds that employ scent in finding some of their food. Oilbirds mostly feed in the air, hovering next to a tree while plucking fruit. Vocal calls are important in these birds for both mating and territorial purposes. These calls vary widely in sound, from the odd, bawling cry of the great potoo (Nyctibius grandis) to the warbling, churring, or whistling songs of various nightjars. Some of these calls are so distinctive that the birds have derived their names from them, for instance the whippoorwill (Caprimulgus vociferus) and the pauraque (Nyctidromus albicollis). Oilbirds make various calls, but their rapid, pulsing clicks are used for echolocation in the dark caves within which they nest and roost. Except for some cave-swiftlets, oilbirds are the only birds known to employ echolocation. It is not known if they use echolocation when outside of their caves. Nightjars exhibit the greatest amount of migration, but most of the tropical forms are sedentary. The poorwill (Phalaenoptilus nuttallii) is a true hibernator, remaining in the temperate zone during winter. Other members of the order are able to enter a temporary torpor by slowing down their metabolism, enabling them to survive periods of inclement weather that can prevent feeding during their limited hours of crepuscular activity. Reproductive behaviour varies within the order. Nightjars make no nest, laying their eggs directly on the ground (or sometimes on rooftops). Frogmouths such as Podargus build nests of twigs in tree branches. The owlet frogmouths lay their eggs in hollow trees or occasionally in tunnels in earthen banks. Oilbirds construct nests on ledges in their caves; these nests are composed of regurgitated fruits, which solidify into hardened structures that are used in succeeding years. Incubation ranges from 19 days in some nightjars to about 35 days in potoos and oilbirds. Nightjar chicks are fed by both parents. At first they eat a regurgitated viscous matter, but later they are fed partially digested insects. They fledge between three and four weeks of age. Oilbird chicks are fed whole fruit after the first two weeks but do not fledge until they are 100 to 120 days old. Additional reading F. Haverschmidt, Birds of Surinam (1968), includes much information on the South American caprimulgiforms. J.P. Chapin, The Birds of the Belgian Congo, vol. 2 (1939), contains readable accounts of the natural history of several tropical nightjars. D.W. Snow, The Natural History of the Oilbird, Steatornis caripensis, in Trinidad, W.I., Zoologica, 46:2748 (1961) and 47:199222 (1962), provides an excellent and readable account of the natural history of that species. The information on nightjar hibernation is scattered among a number of short journal articles, but the reader will find interesting summaries in E.C. Jaeger, Further Observations on the Hibernation of the Poorwill, Condor, 51(3):105109 (1949); and J.T. Marshall, Jr., Hibernation in Captive Goatsuckers, Condor, 57(3):129134 (1955). A review of the later work in this field is presented by G.T. Austin and W.G. Bradley, Additional Responses of the Poorwill to Low Temperatures, Auk, 86(4):717725 (1969). Paul A. Schwartz The Editors of the Encyclopdia Britannica