Nightjars and Frogmouths
The herdsmen, flushing the big-mouthed, moth-like nightjars from pastures or hearing their “night-jarring “voices through the wee hours just when the goats were failing to give milk, decided that these strange birds were the culprits, hence the alternative name of “goatsucker.” Other species also have mysterious names.
Most: nightjars look like big soft moths, dressed as they are in variegated patterns of brown, gray, black, and white. Even their comparatively silent and often dancingly graceful flight suggests moths. Their overall appearance is sleek, with the limpid, generally dark eyes and large heads with tiny bills giving them a “baby-faced” charm that big-headed, small-billed birds always seem to possess. Their wings are usually long and tapered the tail is typically long and wide. Males of tropical savanna and desert include several audaciously ornamented forms. These ornaments, elongated wing oxtail feathers, are employed in courtship dies-plays and are molted or broken off after the breeding season. Nightjars have astonish-kingly large gapes. When one opens its mouth, the whole front of the head becomes a giant glistening cavern fringed with bristles that form an effective insect trap.
The nightjar family is usually subdivided into two subfamilies, the Chordeilinae or nighthawks, and the Caprimulginae or nightjars. The former is restricted to the New World while the nightjars, although having several New World representatives, are also widespread in Europe, Asia, and Africa; the genus Caprimulgus itself contains some 45 species.
Being largely insectivorous, nightjars live mainly in tropical climates or migrate to temperate ones only in warm seasons. Nocturnal counterparts of swallows and swifts, they forage mainly in sustained flight. Woodland dwellers, such as the Dusky nightjar, hawk single insects from a perch, returning to it after each sally.
Nightjars are superbly equipped to cap true insects on the wing at night. A nightjar can engulf large numbers of mosquitoes in a single snap or wheel about and sweep up a Luna moth having an r ohm (4in) wing spread. Small birds are also sometimes taken by larger species such as the chuck-wills-widow, and probably not by accident! There is some indication that these birds can echolocate, thus avoiding collisions with trees while foraging at night.
The nighthawks often feed and migrate in large loose aggregations. A few other species may forage in groups, but perhaps due only to the swarming of insects.
The poor will is the only species of bird known to become torpid for long periods in winter. A Hopi Indian folk tale was recently confirmed when a hibernating poor will was discovered three winters in succession in a rock crevice in southern California. Its body temperature was about r 8°C (64.5°F). The Hopi Indians called the poor will Honcho-” the sleeping one.”
Nightjars are not so much threatened byte the advance of civilization as are many other groups of birds. Most thrive in open, often disturbed habitats, but the whip-poor-will, a true forest dweller once common throughout the eastern USA, has completely disappeared from many now heavily disturbed parts ()fits range. Conservation and management of nightjars require the preservation of habitat and low use of insecticides.
The frogmouths closely resemble true night jars. They sometimes hunt, adopting a liar manner to nightjars, by hawking after insects, but they are also known to chase insects on branches of trees.
Frogmouths are nocturnal birds similar in color to other Caprimulgiformes. The immature birds tend to have plumages either similar to the adult birds or much paler, with a lot of white specks. They have very large, sharply hooked beaks much big-germ than other Caprimulgiformes, with large gapes. However, they have very weak legs and feet. In general, they are considered to be lethargic birds and perhaps the weakest fliers in the order. Their wings are rounded—rather owl-like—and their flights are neither direct nor powerful. They have distinguishing tuft of bristle-like feathers around the nostrils at the base of the beak, which seems partly to conceal the beak and nostrils. Eye color is brown, red, or yellow.
Their hunting method has been described as owl-like, shrike-like, or roller-like. It seems that they pounce on their terrestrial prey items from a regular perch. In addition, some species are thought actually to scour the branches of trees for food. Although the majority of frogmouths appear to be catholicon their choice of woodland, the Tawny frog mouth has a distinct preference for eucalypts.
As well as the geographical variation between the two genera, there are also behavioral and physiological differences: Ponderous has no oil gland whileBatrachostornus does have one. Some species may be migratory: the Papuan frogmouth has been observed on passage from Cape York in northern Australia to New Guinea.
The owlet-nightjars or moth owls are shy dumpy little birds that look like a cross between an owl and a nightjar. They are typically nocturnal, tree-dwelling birds, usually feeding on flying insects; in Australia, they are often found in open country. Owlet-nightjars are closely related to frogmouths.
Owlet-nightjars have relatively large beaks and more forward-facing eyes than the rest of the Caprimulgiformes, which tends to make them seem owl-like, as does their habit of sitting across branches rather than along them. However, they do have typical nightjar features in that they possess long “bristles” around the beak and a wide gap. They fly less erratically than their close relatives.
Males and females are similar. Within several species, there is considerable variation in plumage, and some color variations are recognized as separate species by some authorities. The Large owlet-nightjar usually occurs in a light reddish brown phase or a variegated dark brown and black phase.
Very little is known about the behavior of owlet-nightjars. There is some confusion as to how they catch their prey. Some species are credited with hawking rather like true nightjars, while others are thought to catch their prey on the ground. Analysis of stomach contents has shown that the diet can consist of non-flying prey such as mil-lipids, ants, and also spiders. The fact that they have long, strong legs tends to support the idea that they spend at least some time on the ground chasing insects as well as hawking.
The owlet nightjar is known to breed from September to December. Some pairs have been known to rear two broods in one season. The nestlings have whitish down which is soon replaced. When they leave thinnest they are almost identical to their parents except for a tinge of buff color around the neck. Little is known about the parental care of the young.
MB Potosi’s a Creole name and refers to the call of the Giant photo, one of the five species closely related to nightjars. They have con-coalmen coloration, and roost during the day, resting bolt upright on a tree stump offense post. They feed at night by dashing off from a regular perch to catch flying insects such as moths, beetles, crickets, and termites.
Potoos differ from nightjars in not having facial bristles or the usual comb on the middle claw. However, they do have modified cheek feathers on either side of a very large gape. They have long pointed wings and the shortest tail and legs. The bill is small with a down-curved tip. They have a very large gap partly because the upper mandible can be turned up and the lower mandible turned down.
As Potoos are nocturnal, one would predict they should have loud distinctive calls which they do. In general, their calls consist of a series of whistles and bark-in wows. The very loud “bawd-woo” of the Giant potoos is often credited to something much larger than a bird, often a cat. During the pre-mating period, quacking sounds are repeated every 10 or 20 seconds.
Potoos do not build nests but lay their soli-tarry egg on a tree stump or even in a crevice in the bark. The egg is oval and spotted. Both sexes appear to take it in turns to incubate and the adults rely on camouflage to avoid detection from natural predators but can often be approached and even touched on their own.
Among the Spanish-speaking people of South America they are generally known as guacharo (”the one who cries”), and in Trinidad as diabolic (”little devil”). These loud cries are calls of alarm and of communication with each other, probably also serving to indicate the position of the calling bird to others flying near it. Its other main call—a staccato click that can always be heard when the birds are flying around and undisturbed in the darkness of their caves—is used for echolocation; by picking up echoes from the cave walls and other surrounding objects the oilbird can avoid obstacles in pitch dark-nests.
Their echolocation is, however, much less highly developed than that of bats; the clicks are not supersonic, and echoes are not reflected from very small objects. When oil birds leave their caves at night they stop clicking as they emerge into the open air and, while outside the cave, use what is very sensitive night vision to find their way about. There is some evidence that, in locating some of their food trees, they also use the sense of smell. Many of the fruits of the trees at which they feed are aromatic, and oilbirds have an unusually large and sensitive organ of smell.
Adult oilbirds occupy their nests continuously, returning to them to roost even when they are not breeding. The nests are built of regurgitated fruit matter and grow year by year, in the form of a truncated cone with a saucer-shaped depression at the top. The nesting cycle is extremely long. It is usual for the eggs to be laid at intervals of three days or more, with an extreme of nine days being recorded. Incubation starts with the first egg, so that they hatch, after the long incubation period of about 33 days, in the sequence in which they were laid. At hatch-in, the young are sparsely down-covered, but in their second week, a second and much thicker generation of down feathers grows.
This is succeeded by the plumage of the adult type, which begins to appear at the age of about five weeks. There is no distinct juvenile plumage, nor any other visual character distinguishing a recently fledged young bird from an adult, doubtless because such a distinction would be without function in a dark cave. By about both days, the nestling reaches its maximum weight, and for the remaining 3o or so days it loses weight as the plumage finishes its growth, until both wing length and weight reach the adult condition and the young bird can fly. During the nestling period, both parents feed the young, the same fruits that they eat.
In Trinidad, where oilbirds have been most thoroughly studied, the breeding season is long, lasting for most of the year. It is just possible for a pair of birds to fit two breeding cycles into a year and some do so, but most pairs nest only once per year. In other areas, especially the Andes of Ecuador and Peru, there is evidence that the birds leave their caves for part of the year, perhaps as a consequence of seasonal changes in the availability of fruit; but it is not known where they go. Possibly, colonies alternate between two caves some distance apart. Where seasonal fruit regimes are comp-alimentary. What is certain is that some oil birds, probably young birds. At times wander far from their caves. Stragglers have reached Panama and even the island of Aruba off the coast of Venezuela.
1 thought on “Nightjars and Frogmouths”