Nightjars are medium-sized nocturnal or crepuscular birds in the family Caprimulgidae and order Caprimulgiformes, characterised by long wings, short legs, and very short bills. They are sometimes called goatsuckers, due to the ancient folk tale that they sucked the milk from goats (the Latin for goatsucker is caprimulgus), or bugeaters, their primary source of food being insects. Some New World species are called nighthawks. The English word "nightjar" originally referred to the European nightjar. Nightjars are found all around the world, with the exception of Antarctica and certain island groups such as the Seychelles. They can be found in a variety of habitats, most commonly the open country with some vegetation. They usually nest on the ground, with a habit of resting and roosting on roads. The subfamilies of nightjars have similar characteristics, including small feet, of little use for walking, and long, pointed wings. Typical nightjars, though, have rictal bristles, longer bills, and softer plumage. The colour of their plumage and their unusual perching habits help conceal them during the day. Systematics Caprimulgiformes Previously, all members of the orders Apodiformes, Aegotheliformes, Nyctibiiformes, Podargiformes, and Steatornithiformes were lumped alongside nightjars in the Caprimulgiformes. In 2021, the International Ornithological Congress redefined the Caprimulgiformes as only applying to nightjars, with potoos, frogmouths, oilbirds, and owlet-nightjars all being reclassified into their own orders. See Strisores for more info about the disputes over the taxonomy of Caprimulgiformes. A phylogenetic analysis found that the extinct family Archaeotrogonidae, known from the Eocene and Oligocene of Europe, are the closest known relatives of nightjars. Caprimulgidae Traditionally, nightjars have been divided into two subfamilies - the Caprimulginae, or typical nightjars with 79 known species, and the Chordeilinae, or nighthawks of the New World, with 10 known species. The groups are similar in most respects, but the typical nightjars have rictal bristles, longer bills, and softer plumage. Their soft plumage is cryptically coloured to resemble bark or leaves, and some species, unusual for birds, perch along a branch rather than across it, helping to conceal them during the day. The subfamilies of nightjars have similar characteristics, including small feet, of little use for walking, and long, pointed wings. The common poorwill, Phalaenoptilus nuttallii, is unique as a bird that undergoes a form of hibernation, becoming torpid and with a much reduced body temperature for weeks or months, although other nightjars can enter a state of torpor for shorter periods.