nightjar

n.
A goatsucker, especially Caprimulgus europaeus of Europe, having gray and brown mottled plumage with long, slender white wings and a short bill.

[NIGHT + JAR² (from its harsh call).]

For more information on nightjar, visit Britannica.com.

(Caprimulgidae)

Class: Aves

Order: Caprimulgiformes

Suborder: Caprimulgi

Family: Caprimulgidae

Thumbnail description
Small to medium-sized nocturnal and crepuscular birds with small bill, large gape and eyes, long wings and tail, short legs, cryptic coloration, and comb-like serrations on the claw of middle toe

Size
6–16 in (15–40 cm); 0.7–6.6 oz (20–188 g)

Number of genera, species
19 genera; 77 species

Habitat
Semi-desert, grassland, savanna, woodland, and forest

Conservation status
Critically Endangered: 2 species; Endangered: 2 species; Vulnerable: 3 species; Near Threatened: 4 species

Distribution
Nearly cosmopolitan, but absent from Arctic, Antarctic, and most oceanic islands

Evolution and systematics

Fossils of a single undescribed species of Caprimulgidae have been reported from the Middle Eocene (50.5–42 million years ago) oil shales at Messel in Germany, providing the only fossil record of a true nightjar from the Tertiary. Other fossils suggest that the closest relatives of the nightjars, the potoos (Nyctibiidae) and frogmouths (Podargidae), had diverged by the Eocene, and estimates based on differences in their DNA structures likewise point to early Tertiary origins of the nightjars.

Division of the Caprimulgidae into two subfamilies, the nighthawks (Chordeilinae) and nightjars (Caprimulginae), is based on several characters, of which the absence of rictal bristles in nighthawks is the most obvious (the rictus is the gape of a bird's mouth). Compared to the nightjars, nighthawks tend to have longer wings and tail and more often have a notched or forked tail, but there are exceptions. Originally, the Chordeilinae was established only for several American genera of nighthawks, but the African brown nightjar (Veles binotatus) and the Asian to Australasian eared nightjars (genus Eurostopodus) show similar characters, so these also should probably be included in the Chordeilinae. However, the so-called nacunda nighthawk (Podager nacunda) has well-developed rictal bristles and other characters like those of the true nightjars, so it seems best placed in the Caprimulginae.

The elaborately lined plumages of nightjars differ little between some species, yet other species are variable in color. It is therefore often difficult to classify nightjars into species and there is a tendency to rely on differences in songs and other evidence in seeking the best possible treatment, especially when similar forms occur in neighboring regions without range overlap. Such unsolved problems in the classification of species exist with the African fiery-necked nightjar (Caprimulgus pectoralis) and the closely related black-shouldered night-jar (C. nigriscapularis), which differ very slightly in appearance and have slightly different songs. Likewise, treatment of the eastern and western American forms of the whip-poor-will (Caprimulgus vociferus) as subspecies of a single species remains tentative because they are very similar in coloration but have slightly different voices.

Physical characteristics

Nightjars are small to rather large Caprimulgiformes with a relatively large head, large eyes, short neck, and very short legs. Although the bill is tiny, the huge gape allows large insects to be swallowed whole. The base of the bill often has strong rictal bristles (lacking in Chordeilinae), which may serve to direct prey into the gape, to protect the eyes from hard prey, or both. Wings are long to very long and more or less pointed, and the tail can be rather short to long with a graduated, rounded, square, notched, or forked tip. Toes are slender, and the claw of the middle toe has comb-like serrations that provide a unique feature of the Caprimulgidae within the order Caprimulgiformes.

A few species have elaborate long plumes that probably serve to exaggerate displays. In three South American species of the genus Macropsalis, adult males have deeply forked tails with greatly elongated outer feathers, which converge at their tips in the swallow-tailed nightjar (M. segmentata) and long-trained nightjar (M. forcipata) but converge subapically then diverge slightly at the extreme tips in the lyre-tailed night-jar (M. lyra). Adult males of two African species develop a single greatly elongated inner secondary feather that is retained only for part of each year. In the standard-winged nightjar (Macrodipteryx longipennis) the elongated feather consists only of a wire-like shaft except near the tip where it widens into a broad standard so that when the bird flies it seems to be closely followed by two large dark butterflies. The closely related pennant-winged nightjar (M. vexillarius) has the inner secondary modified to form a long narrow streamer. The exaggerated display plumes of the genera Macropsalis and Macrodipteryx appear to be associated with lek displays (a lek is a mating ground) in these species, which are the only polygynous (more than one female mate at a time) nightjars.

Nightjar plumages are marked in mainly somber shades of brown, gray, buff, tawny, or rufous and are often beautifully patterned with bars, streaks, and blotches to give some of the finest examples of concealing coloration of any animals. Thus, desert birds such as the aptly named golden nightjar (Caprimulgus eximius) tend to be pale to match the prevalent substrate, whereas birds of the dark forest interior such as the brown nightjar are predominantly very dark brown or blackish. White or pale signal markings used in nightjar displays are normally kept concealed inside closed wings or tail or beneath the throat when the birds are at rest; they are revealed during nocturnal display flights or when singing.

Distribution

The range of caprimulgids is much wider than that of any other family in the order Caprimulgiformes, and many of the species are migratory, unlike the essentially sedentary birds in other families. Only the Arctic, Antarctic, and remote oceanic islands lack nightjars. The greatest diversity of species occurs in the tropics and subtropics. In North America the common nighthawk (Chordeiles minor) extends far north into Canada. In the Old World the European nightjar (Caprimulgus europaeus) extends north to the boreal forests of Finland and east to the semi-desert steppes of Mongolia. In the Southern Hemisphere, the band-winged nightjar (Caprimulgus longirostris) ranges south to Chile.

The diet of flying insects prevents most nightjars from remaining all year in regions with cold winters, although the common poorwill (Phalaenoptilus nuttallii) does so by hibernating. Other species that breed at high latitudes are long-distance migrants, the most striking examples being the common nighthawk, which leaves North America to winter in South America as far south as northern Argentina, and the European nightjar, which leaves Europe and Asia to winter in Africa south of the Sahara. Shorter migrations are under-taken by species such as the red-necked nightjar (Caprimulgus ruficollis), which breeds in Spain and winters south of the Sahara in west Africa, and the rufous-cheeked nightjar (C. rufigena), which breeds in South Africa and neighboring countries but migrates to spend the southern winter in tropical and subtropical countries of central Africa, especially Cameroon. Other species make seasonal movements from one vegetation zone to another within the tropics.

Habitat

Nightjars and nighthawks occupy a much broader range of habitats than do members of other families of Caprimulgiformes, which are often closely restricted to the ancestral rainforest habitats of the order. Instead of requiring trees for nest sites and hunting perches, the Caprimulgidae have evolved a predominance of ground nesting, and many species have the ability to hunt in sustained flight or by sallying from the ground, which enables them to live in grasslands, steppes, semi-deserts, savannas, and open woodlands. Few nightjar and nighthawk species live in closed forests, including both lowland and montane rainforests, and it is likely that species inhabiting such forests have reinvaded from more open habitats.

Several species have become urban dwellers, finding suitable nest sites on flat roofs of city buildings and plenty of insects to hunt around street lights and high in the air. Common nighthawks have adopted many North American cities over the twentieth century, and band-winged nightjars have colonized Rio de Janeiro (Brazil), Madagascar nightjars (Caprimulgus madagascariensis) occur in towns in Madagascar, and savanna nightjars (C. affinis) are at home in such large Indonesian cities as Jakarta and Surabaya.

Behavior

Like other Caprimulgiformes, nightjars and nighthawks are essentially crepuscular and nocturnal birds that sit quietly in roosts during the day and become active from around dusk until dawn. The timing of activities varies among species, season, and sometimes according to phase of the moon. The common nighthawk begins feeding much earlier in the evening than most nightjars, often hunting in the last of strong daylight well before dusk. Other species commonly remain immobile until little light is left and human observers can scarcely distinguish colors in the twilight; the late start to activity presumably serves to reduce risks of predation. Many nighthawks and nightjars do not hunt during the middle hours of moonless nights, apparently because they are unable to see prey when there is insufficient light; this hypothesis seems to be confirmed by the fact that some feed for much longer on moonlit nights.

Common poorwills are able to become torpid and hibernate for months in a rock crevice during cold winter conditions, but there is no evidence that any other species of the family makes such extensive use of torpor. Nevertheless, torpor lasting at least several hours has been reported from common nighthawks, lesser nighthawks (Chordeiles acutipennis), and European nightjars that were cold, hungry, or both. It seems likely that entering torpor to reduce energy requirements is among the adaptations of Caprimulgidae that enable them to cope with an uncertain food supply.

Most nightjars have striking territorial songs that vary from clear loud whistles or whistled phrases to sustained churring, knocking, or purring sounds. The name nightjar derives from the prolonged jarring chur of the European nightjar, and the nocturnal vocalizations provide the first indication of the presence of most nightjar species for layman and ornithologist alike. Besides the song, the vocabulary of several of the better-known species includes a range of calls. The European nightjar uses at least 10 different types of calls, among which are special flight, alarm, threat, mating, brood-summoning, and food-begging calls. Mechanical wing clapping is also a feature of territorial display in the European nightjar and many other species.

Feeding ecology and diet

The diet of nightjars and nighthawks consists largely of insects. It typically includes beetles, moths, bugs, orthopterans, flies, termites, and flying ants, most if not all of which are caught in flight. Some nightjars take a small proportion of food from the ground or pick it from vegetation while hovering, and this behavior doubtless accounts for occasional wingless beetles, ants, or caterpillars that are eaten. Besides insects, spiders are occasionally eaten and there are a few records of centipedes, millipedes, and small snails in nightjar stomach contents. The rare records of seeds and other vegetable matter, however, may represent material accidentally ingested along with insects. The largest of all the nightjars, the chuck-will's-widow (Caprimulgus carolinensis), rarely eats tree frogs and very small birds, mainly warblers (Parulidae).

Two principal feeding techniques are used by nightjars and nighthawks, both of which lead to seizing prey in the bill while in flight and swallowing it whole. Hawking involves sustained flights during which the bird may catch numerous insects, often high in the air, but sometimes also low over the ground or water. Sallying involves a shorter flight from a perch or from the ground to catch an insect before returning to a perch. Most nighthawks and some nightjars rely almost exclusively on hawking for food, their long wings and strong flight evidently being adaptations for this. On the other hand, many nightjars of wooded or forest habitats rely mainly or exclusively on sallying. Others use both techniques. The European nightjar apparently chooses between them according to abundance and location of prey.

Because most feeding takes place in near-darkness, there has been much misunderstanding of how it is carried out. Many old accounts implied that nightjars fly about with the bill open, using it in the manner of a net to scoop up insects. This may occasionally be true, as when the bird flies through dense swarms of tiny insects such as mosquitos, but it is not the usual technique. Detailed studies of common nighthawks, common poorwills, and European nightjars show that individual insects are targeted and the bird only opens its bill to seize them when they are closely approached. There seem to be clear preferences for larger insects, and limitations of the birds' eyesight may preclude feeding on the smallest prey (as opposed to considerations of cost-effectiveness).

Nightjars are adept at locating concentrations of insect prey and taking advantage of local superabundances of insects. Swarms of winged ants and termites, emerging caddis-flies, and mayflies at lakes may be targeted. Concentrations of insects around streetlights provide attractive food sources and artificial light may allow feeding later into the night than is possible under natural conditions. Nightjars also feed on insects flushed by grass fires in savanna regions of Africa and in open pine forests of the southeastern United States.

Reproductive biology

Most nightjars are monogamous, with pairs mating for life or breeding together for one season. Occasionally they may change partners between clutches in the same season. The pennant-winged and standard-winged nightjars have a different breeding strategy from other nightjars and are probably polygynous.

Breeding seasons of Caprimulgidae appear to be timed to coincide with presence of abundant flying insects needed to feed young. Species with northern ranges, such as common nighthawks or European nightjars, are rather late arriving as spring migrants and do not lay eggs until late spring. In tropical savannas, breeding typically occurs as the flush of new vegetation following seasonal rains allows a peak of insect abundance. The breeding season may be more prolonged in regions of the tropics with rain for much of the year, although caprimulgids usually avoid breeding in the months with high rainfall.

Unlike several other families of Caprimulgiformes, none of the nighthawks or nightjars makes a nest. Most choose a simple hollow in the ground, apparently without deliberately deepening it. A few species nest in depressions in tree branches, high above the ground in the case of short-tailed nighthawks (Lurocalis semitorquatus). The only account of the nest of the brown nightjar was of a bird apparently incubating or brooding on top of an arched frond of a Raphia palm in the Central African Republic. Nesting above ground is rare in Caprimulgidae and is apparently a secondary development from ground nesting, as no nest-building or other special adaptations are known to be involved.

Clutches are of one or two eggs, typically a single egg in tropical species and two eggs or variably one or two in others. Eggs are unmarked white in some species (for example most eggs of common poorwills), but more often they are spotted or blotched with shades of brown, gray, lavender, or black, which promotes concealment. Nevertheless, it is likely that there is little need for concealing coloration with eggs of most nighthawks and nightjars because an incubating adult bird would normally cover them almost continuously.

The role that males and females play in incubation varies considerably among species. In freckled nightjars (Caprimulgus tristigma) and fiery-necked nightjars, males incubate at night and the more cryptically colored females do so by day. In European nightjars, the male takes only a short stint at dusk and dawn while the female is away feeding. In polygynous pennant-winged and standard-winged nightjars, only the female incubates eggs. Incubation periods are unknown for many species, but typically they last about 17–20 days.

Young hatch with a covering of soft down that is replaced by the emerging juvenal feathers after about a week. Small young in down are brooded most of the time, but when they grow juvenal feathers they are typically brooded only when it is cold or wet. Even quite small young commonly walk from the original nest site and after a few days they may be many yards away from it. Fledging is a gradual process in that development of flying skills is progressive, with weak flapping usually possible after about two weeks but strong flight and independent feeding not until the fourth week. Typically, both parents are involved in brooding the young and feeding them on regurgitated insect food, but only the female carries out these duties in polygynous species.

Several of the nightjars are known to raise two broods each breeding season, and most if not all will lay replacement clutches if the first is lost. The two broods in European night-jars somewhat overlap, a response to the short northern breeding season. This is achieved because the male takes full charge of the young of the first brood while the female incubates the second clutch.

Many nightjar eggs and young are lost to predators, including birds such as crows, mammals such as rats and mice, and snakes. Much of the breeding behavior of nightjars is adapted to reduce risks of predation. For example, incubating birds crouch motionless with eyes almost closed, unwilling to leave the nest until almost trodden upon. When detected at the nest, adult nighthawks and nightjars commonly show threat or distraction displays intended to intimidate or distract potential predators. These displays have been well studied in lesser nighthawks; ground predators or less dangerous intruders such as sheep or rabbits are confronted with a threat display in which the bird faces the intruder, erects its plumage with spread wings and tail, and at high intensity gapes and hisses. Walking humans or crows are met with distraction displays of disablement-lure type, in which the adult bird typically flutters along the ground as if injured, with trailing wings or flopping flight, attempting to lure the intruder away from eggs or chicks.

Conservation status

Two nightjar species are Critically Endangered: Jamaican poorwill (Siphonorhis americana; last reliably recorded in 1859) and Puerto Rican nightjar (Caprimulgus noctitherus). Two species are Endangered: white-winged nightjar (C. candicans) and Itombwe nightjar (C. prigoginei). Three species are listed as Vulnerable: Heinrich's nightjar (Eurostopodus diabolicus), Bonaparte's nightjar (C. concretus), and nechisar nightjar (C. solala). Four species are classified as Near Threatened: Salvadori's nightjar (C. pulchellus), sickle-winged nightjar (Eleothreptus anomalus), Chocó poorwill (N. rosenbergi), and plain-tailed nighthawk (Nyctiphrynus vielliardi). An additional three species are listed as Data Deficient.

Significance to humans

No nightjar species is of much economic importance and many of them are retiring birds that are little known to local people. However, their strange and often beautiful nocturnal voices attract attention, and several species are the subject of folklore. A recurrent theme is the myth that nightjars suck milk from the teats of goats, resulting in widespread use of names such as goatsucker in English, Ziegenmelker in German, and Succiacapre in Italian. The scientific name of the principal nightjar genus, Caprimulgus, has the same origin, being formed from the Latin words capra for a goat and mulgere to milk. The basis for this groundless belief may lie in the frequent observation of milk on the ground near goats with newly-born kids coupled with presence of nightjars feeding on insects near the animals at night and the fact that night-jars have an immensely wide mouth.

Other widespread beliefs are that the nocturnal calls of various nightjars are bad omens that may even foretell death. One local name for the European nightjar, the German Todtenvögel, means death bird. Elsewhere, the number of successive calls given by some South American nightjars was believed to foretell the number of years for which the listener would live, and other nightjar species were thought to represent spirits of the dead.

Species accounts

Common nighthawk
Spotted nightjar
Common poorwill
Chuck-will's-widow
Whip-poor-will
Gray nightjar
European nightjar
Large-tailed nightjar
Fiery-necked nightjar
Standard-winged nightjar

Resources

Books:

Cleere, N. "Nightjars." In Handbook of the Birds of the World. Vol. 5, Barn-owls to Hummingbirds, edited by Josep del Hoyo, Andrew Elliott, and Jordi Sargatal. Barcelona: Lynx Edicions, 1999.

Holyoak, D.T. Nightjars and Their Allies. Oxford: Oxford University Press, 2001.

[Article by: David T. Holyoak, PhD]

Because of their silent flight, large eyes, and weird purring cry, nightjars were regarded as uncanny. In Yorkshire they were said to be the souls of unbaptized infants, wandering for ever, and/or to be the sinister Gabriel, Ratchets. In Shropshire and Cheshire they were called ‘lich fowl’, i.e. ‘corpse birds’, and in several counties the ‘night hawk’, ‘night raven’, or ‘night crow’, a term taken from a biblical list of birds which are ‘an abomination’ and should never be eaten (Leviticus 11: 16). They were also commonly called ‘goatsuckers’, being thought to suck the udders of goats and cows, infecting them with disease (Swainson, 1885/1965: 97-8).

This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)