The Latin generic name refers to the old myth that the nocturnal nightjar suckled from goats, causing them to cease to give milk.

Their densely patterned grey and brown plumage makes individuals difficult to see in the daytime when they rest on the ground or perch motionless along a branch, although the male shows white patches in the wings and tail as he flies at night.

The preferred habitat is dry, open country with some trees and small bushes, such as heaths, forest clearings or newly planted woodland.

The male European nightjar occupies a territory in spring and advertises his presence with a distinctive sustained churring trill from a perch.

Although it suffers a degree of predation and parasitism, the main threats to the species are habitat loss, disturbance and a reduction of its insect prey through pesticide use.

Despite population decreases, its large numbers and huge breeding range mean that it is classified by the International Union for Conservation of Nature as being of least concern.

The largest and most widespread genus is Caprimulgus, characterised by stiff bristles around the mouth, long pointed wings, a comb-like middle claw and patterned plumage.

[10] There are six recognised subspecies, although the differences are mainly clinal; birds become smaller and paler in the east of the range and the males have larger white wing spots.

[4][13] The adult of the nominate subspecies has greyish-brown upperparts with dark streaking, a pale buff hindneck collar and a white moustachial line.

[15] The male European nightjar's song is a sustained churring trill, given continuously for up to 10 minutes with occasional shifts of speed or pitch.

[16] Even a singing male may be hard to locate; the perched bird is difficult to spot in low light conditions, and the song has a ventriloquial quality as the singer turns his head.

[4] Recent tracking data has revealed that European nightjars have a loop migration from Western Europe to sub-equatorial Africa where they have to cross several ecological barriers (the Mediterranean Sea, the Sahara and the Central African Tropical Rainforest).

[3] The European nightjar is a bird of dry, open country with some trees and small bushes, such as heaths, commons, moorland, forest clearings or felled or newly planted woodland.

When breeding, it avoids treeless or heavily wooded areas, cities, mountains, and farmland, but it often feeds over wetlands, cultivation or gardens.

The cryptic plumage makes it difficult to see in the daytime, and birds on the ground, if they are not already in shade, will turn occasionally to face the sun thereby minimising their shadow.

[3] Like other aerial birds, such as swifts and swallows, nightjars make a quick plunge into water to wash.[23] They have a unique serrated comb-like structure on the middle claw, which is used to preen and perhaps to remove parasites.

[2] In cold or inclement weather, several nightjar species can slow their metabolism and go into torpor,[24] notably the common poorwill, which will maintain that state for weeks.

[25] The European nightjar has been observed in captivity to be able to maintain a state of torpor for at least eight days without harm, but the relevance of this to wild birds is unknown.

Returning males arrive about two weeks before the females and establish territories which they patrol with wings held in a V-shape and tail fanned, chasing intruders while wing-clapping and calling.

[27] A study specifically looking at the European nightjar showed that the phase of the moon is a factor for birds laying in June, but not for earlier breeders.

[3] Birds hunt over open habitats and woodland clearings and edges, and may be attracted to insects concentrating around artificial lights, near farm animals or over stagnant ponds.

Nightjars pursue insects with a light twisting flight, or flycatch from a perch; they may rarely take prey off the ground.

[39] Adults may be caught by birds of prey including northern goshawks, hen harriers, Eurasian sparrowhawks, common buzzards, peregrines[39] and sooty falcons.

Its scarcity and the fact that it is the only one of its genus found in nightjars support the suggestion that it has crossed over from close relatives that normally infect owls.

[4] As ground-nesting birds, they are adversely affected by disturbance, especially by domestic dogs, which may destroy the nest or advertise its presence to crows or predatory mammals.

[30][44] In Britain and elsewhere, commercial forestry has created new habitat which has increased numbers, but these gains are likely to be temporary as the woodland develops and becomes unsuitable for nightjars.

[45] Poets sometimes use the nightjar as an indicator of warm summer nights,[17] as in George Meredith's "Love in the Valley"; Lone on the fir-branch, his rattle-notes unvaried Brooding o'er the gloom, spins the brown eve-jar Wordsworth's "Calm is the fragrant air": The busy dor-hawk chases the white moth With burring note.

or Dylan Thomas's "Fern Hill": and all the night long I heard, blessed among stables, the nightjars flying with the ricks Nightjars sing only when perched, and Thomas Hardy referenced the eerie silence of a hunting bird in "Afterwards": If it be in the dusk when, like an eyelid's soundless blink The dewfall-hawk comes crossing the shades to alight Upon the wind-warped upland thorn.

[17][34] This ancient belief is reflected in nightjar names in other European languages, such as German Ziegenmelker, Polish kozodój and Italian succiacapre, which also mean goatsucker, but despite its antiquity, it has no equivalents in Arab, Chinese or Hindu traditions.

[49] Like "gabble ratchet" (corpse hound), it may refer to the belief that the souls of unbaptised children were doomed to wander in nightjar form until Judgement Day.