goatsucker, common name for nocturnal or crepuscular birds of the order Caprimulgiformes, which includes the frogmouth, the oilbird, potoos, and nightjars. Goatsuckers are medium in size and are found in the temperate and tropical zones of both hemispheres. The name goatsucker is based on an ancient belief that these birds fed on goats' milk by night, but their presence near such animals was no doubt due to the insects attracted by the goats. With their long, pointed wings, weak feet, and small, wide-gaping bills fringed with bristles, goatsuckers have been called flying insect traps. Like their relatives the owls, they are protected by brown, gray, and black coloring, and their lax and fluffy feathers render their flight almost noiseless. This and their monotonous, repetitious song are factors in their superstitious significance. Their weird cries are reflected in the common names for many of the species, e.g., whippoorwill, chuck-will's-widow, poorwill, poor-me-one, potoo, and pauraque. The whippoorwill is common in the E United States. Ornithologists have discovered that the whippoorwill, unlike other birds, hibernates during the winter instead of migrating. Its body temperature drops from 102℉ (39℃) to 65℉ (18.3℃), its breathing slows, and its digestion ceases until spring brings the return of the insects that constitute its diet. The whippoorwill's flight, like that of the swift, is graceful and erratic; it sometimes swoops downward and then stops abruptly, producing a booming sound as it spreads its wings to brake. The larger (12 in./30 cm) chuck-will's-widow (Caprimulgus carolinensis) is found in the South and the poorwill (7 in./17.5 cm) in the West. The nighthawk (Chordediles popetue), or bull bat, common in all parts of North America N to Labrador, is the most diurnal of the goatsuckers; it is active at twilight and daybreak, whereas the others fly only at night. The nighthawk's familiar cry is a nasal “peent.” The oilbirds of South America have sonar devices that enable them to fly in total darkness. The pauraque, or cuiejo, is a Central American goatsucker, and the aptly named frogmouths are native to Australia and Asia. Goatsuckers are classified in the phylum Chordata, subphylum Vertebrata, class Aves, order Caprimulgiformes.

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