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Caprimlgiformes - Goatsuckers
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Caprimulgiformes - Goatsuckers
Families: Owlet-nightjars, Frogmouths, Oilbirds, Potoos, Eared-nightjars,
   Nighthawks and Nightjars
Hibernation and hypothermy
Tawny Frogmouth, Oilbird, Eurasian Nightjar, Nighthawk, White-tailed Nightjar
  Order Caprimulgiformes - Owlet-Nightjars, Frogmouths,
       Oilbirds, Potoos, Eared-Nightjars, and Goatsuckers
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  113 species, 20 genera (Sibley and Monroe, 1990). Clements (2007) lists 120 species. Sibley and Ahlquist (1990) place the owls and nightjars together in one order, the order Strigiformes based on DNA evidence. This is followed by the Encyclopedia of Life. The Tree of Life groups the Apodiformes (hummingbirds and swifts) and Owlet-Nightjars as sister groups. This clade is then a siser group to the other Caprimulgiformes. Sibley and Ahlquist (1990) separate the frogmouths into two families but most current sources keep them together. It has been suggested that Frogmouths may be distinct enough to merit a separate order, Order Podargiformes. Pending more evidence, we'll keep the traditional arrangement.
   Owlet-Nightjars and caprimulgids are crepuscular and nocturnal birds and many feed on flying insects. They combine some of the characters of owls and swifts. Most species are active at twilight or at night. During the day they perch on the ground or lengthwise on a branch.  (Our Nighthawk, Chordeiles minor, is an exception to this rule - they may be active during the day but are most obvious toward sunset.)
Goatsuckers have a deeply cleft gape. The bill is small and weak. Their feet have the first toe directed posteriorly and toes 2-4 forward ("anisodactyl") and the hypotarsus is complex. The palate is schizognathous or desmognathous. Pelvic muscles are AXY (or XY). there are two carotids in caprimulgids, only the left in podargids. Flexor tendons are Type 5a. The syrinx is bronchial or tracheo-bronchial. Nares are holorhinal and impervious. The skin is very thin (like wet tissue-paper). They have 10 primaries, 11-13 secondaries, and 10 tail feathers. The aftershaft is small and adult downs are restricted to apteria (areas between the contour feather tracts). Their soft plumage is cryptically colored. Frogmouths and potoos have powder downs. There are 13-15 cervical vertebrae. The oil gland is variable.  
   Goatsuckers do not build a nest. They lay 2 (1-3) eggs on bare ground or fallen leaves. Our nighthawk sometimes nests on graveled roofs of buildings. Eggs are cryptically colored. Both sexes incubate for 16-21 days and brood the young. Young are covered with down and are nidicolous but become active, running around near the nest at night and hiding under the virtually indistinguishable female during the day. Their fecal and urinary wastes are deposited around the nest forming a ring that may reveal the nest's location (the nest is said to be "fouled"). Adults forage and collect insects in their crops. Upon returning to the nest they feed young the regurgitated  crop contents. Most caprimulgids feed mainly on flying insects captured in continuous flight.
   Goatsuckers are found worldwide in tropical and temperate regions except New Zealand and many oceanic islands.
   All of the North American caprimulgids are found in one family, the Caprimulgidae (below). However, there are a diverse group of other taxa found elsewhere.
  Family Aegothelidae - Owlet-Nightjars
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  8 (9) species in 1 (2) genera (Aegotheles, Euaegotheles). Australia, New Guinea, New Caledonia and the Moluccas. They may share a more recent common ancestor with the Apodiformes (and could be placed in a separate order, Order Aegotheliformes. This order plus the Caprimulgiformes and Apodiformes then form a clade called Cypselomorphae. The owlet-nightjars and Apodiformes form the clade Daedalornithes. Stay tuned.
   Owlet-nightjars have a resemblance to owls. They have a large head, large eyes and a flat bill with an extraordinarily wide gape. They are small to medium birds with soft plumage that is cryptically colored. The tarsus is longer than in other caprimulgids. Their feet are small and weak but larger than those of a frogmouth. The outer toe has 5 phalanges and the middle toe is not pectinate. Nostrils are located near the tip of the bill and are obvious. The bill is very small but their mouth opens to an enlarged gape that is surrounded by rictal bristles. Their plumage is soft. There are no powder downs and no caeca. Wings are short - they have 10 primaries and about 11 secondaries.
   They are nocturnal - spending the days hiding in tree holes or in dense vegetation or crevices in cliffs. They perch crosswise on branches. They are usually solitary but may mate for life. They feed on flying insects (beetles, moths, grasshoppers, etc.) and terrestrial invertebrates. They are found in lowland tropical forests and range to more open woodland and shrubs. They are less frequent in rain forests. They are sedentary and occupy their territory year round.
   Little is known about their breeding. They appear to nest in holes, both parents lining the nest. They lay 2-5 white or spotted eggs which are incubated mainly by the female for about 26 days. Both parents feed the young. Fledging takes 21-29 days.
  Family Podargidae - Frogmouths
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  13 species, 3 genera. South and southeast Asia, Australasia.
   Sibley and Monroe (1990) separate the frogmouths into 2 families:
      Family Podargidae - Australian Frogmouths (3 species, 1 genus)
      Family Batrachostomidae - Asian Frogmouths (11 (10) species, 1 (2) genera)
   Frogmouths are an ancient group of secretive and nocturnal birds. They are relatively small to medium in size - Podargus - Australia, larger birds, Batrachostomus - Asia smaller birds. They have a large head and eyes, a large, flat, hooked bill with a gigantic frog-like gape used to catch insects. Their nostrils are slit-like, located near the base of the bill, and protected by an operculum with overhanging feathers. They all have short bristles on the forehead and ear coverts - they may help in sensing prey? (A third genus was recently discovered in the Solomons - Bougainville, Isabel, and Guadalcanal - to include the Solomon Islands Frogmouth, Rigidipenna inexpecta).Tawny Frogmouth
   Frogmouths have broad, rounded wings and a long tail. Their flight is weak - they have small legs and feet. They have 5 phalanges in the outer toe and the middle toe is not pectinate. The fourth toe is reversible.
  Their plumage is cryptic with stripes and bars giving a mottled effect. They have large powder down patches on each side of the rump.
   They are nocturnal. Most are solitary. They rest horizontally in branches during the day - we found a family of Papuan Frogmouths, Podargus papuensis, roosting in a tree in Port Darwin, Queensland, in northern Australia on a recent visit. They prefer a high branch and look like a broken stump. The picture to the right is of a Tawny Frogmouth, Podargus strigoides.
   They bathe during showers, fluffing their feathers and swaying from side-to-side. They spread their wings like cormorants to dry.
   They are best located by their calls/song. The make repeated  hooting or booming sounds that are often repeated. Some duet. They live in evergreen tropical forests, dry woodlands, eucalyptus groves and, sometimes, in open and suburban areas. They feed on the ground or in trees - they do not "hawk" for prey. They eat fairly large tough insects (beetles and cicadas) as well as small animals. They are sedentary.
   Pairs occupy their territory year round. Asian species build small, cup shaped nests lined with down and lay 1 egg. Australian species build bulkier nests with twigs and lay 1-3 white eggs. The female incubates; both parents feed the young. Chicks stay in the nest until they can fly.
  Family Steatornithidae - Oilbirds
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  1 species, 1 genus (Steatornis caripensis). Panama, northern South America. Their closest relatives are probably the potoos with nightjars and frogmouths being more distant relations. Their is some suggestion that it be placed in a separate order.
   Oilbirds are are medium-sized, slim, long-winged birds. Sexes are similar but males are slightly larger. They are reddish-brown with white spots on the nape and wings. They are buff with white underneath. Tail feathers are stiff. Their eyes are large and they have good night vision which they use in feeding. They also have an acute sense of smell that aids in locating fruit. The bill is hard, strong, owl-like, and has a subterminal tooth - it is broad at the base, hooked at the tip, and opens into a very wide gape. The rostrum is movably articulated with the skull and the gape is surrounded by large rictal bristles (up to 2" long). Their wings are large and the primaries are deeply slotted, enabling them to carry massive loads of fruit back to the nest to feed their young. They are able to hover and twist in flight as they feed or fly through restricted areas. Their tail is long and graduated. They have short legs and long anisodactyl toes which cause them to perch awkwardly - they are small and almost useless. There are 15 cervical vertebrae. The syrinx is bronchial.
Oilbird, Steatornis caripensis.
Asa Wright Nature Center, Trinidad
Photo by Ed Konrad
   Oilbirds are one of the few species of bird known to use echolocation (Collocalia swiftets also use echolocation). They emit clicks at 7 Kcycles/second and detect reflected sound to navigate in their nesting/roosting caves in total darkness (these clicks are in the audible sound range and can be heard in their caves). It also utters harsh screams in caves as they enter and leave.    Oilbirds are nocturnal and social. They roost in caves during the day and emerge at dusk to feed - traveling up to 100 miles as they forage. They live in tropical and subtropical forests and require caves for roosting and nesting.    Oilbirds form colonies with thousands of individuals. Many colonies disperse after breeding and the location and behavior of the birds are poorly known at this time. They feed on the ripe  fruit of the Oil Palm and tropical laurels (all other caprimulgids are insectivorous). They use vision in feeding.
.  They are monogamous. Both sexes care for the young. Within colonies, breeding activities are synchronized among residents. Their nest is a shallow bowl placed high on a ledge, often far from the cave entrance - often over water. It includes palm seeds and droppings (feces), glued together with saliva. Nests may be reused, increasing in thickness with each brood. They lay 2-4 white eggs. Incubation and fledging require 3-4 months. Chicks hatch with a gray down that is replaced by a second dense coat of down at about 3 weeks. Adult feathers emerge at about 3 months. Young squabs become very fat before fledging (and have been harvested commercially for oil in the past - hence the name oilbird). Little is known about post-fledging parental care.
  Family Nyctibiidae - Potoos
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  7 species, 1 genus (Nyctibius). Southern Mexico to Brazil, Jamaica, and Hispaniola.
   Potoos are nocturnal insectivores. They feed by catching insects in flight. Pootoos are small to medium-sized birds with large heads and a small, hooked bill - the maxilla has a subterminal tooth but there are no rictal bristles. Like other caprimulgids, their gape is cavernous. They have large eyes with small folds on the upper eyelid. The iris is yellow or orange. Their eyes have "slits" in the nictitating memberane which may allow the bird to sense movement with their eyes are covered (keeping the highly reflective tapetum from giving them away during the day). They have long wings and a long tail. They have a short tarsus. The fifth toe has 5 phalanges and the hallux has 3. The middle toe is not pectinate. Their feet are relatively weak but they perch easily.
   Sexes are alike. Pootoos are cryptically colored with individual variations. There are large powder down patches on the sides and breast. They are nocturnal and solitary. Most live in the forest canopy where they perch upright during the day, remaining frozen and looking like part of a stump or branch. They sing at night. They live in forested tropical lowland areas (one species is found in cloud forests of the Andes). They eat large insects - termites, moths, beetles, grasshoppers, etc. - usually caught in flight or picked from vegetation. One was found with a small bird in the gizzard. They swallow their prey whole.
   Potoos are monogamous and share duties. They build no nest but lay a single spotted egg on a broken tree stub or depression on a branch. Incubation lasts ~30 days. One parent incubates during the day and duties are shared at night. The chick is downy and remains on the branch for about 2 months before taking flight. Once they are too large to hide under their parents' feathers, they also assume to same erect frozen posture and rely on their camouflage to avoid predation.
  Family Eurostopodidae - Eared-Nightjars
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  7 species, 1 genus (Eurostopodus). Australia, New Guinea, the Solomons, New Caledonia, southeast Asia, India to East Pakistan, southwestern China and the Philippines. Dickinson (2003) includes this group as the Subfamily Eurostopodinae withn the Family Caprimulgidae. Clements (2007) also placed them within the Caprimulgidae.
   These caprimulgids resemble nightjars to others but tend to be larger and darker in color and lack long rictal bristles. They have long, erectile tufts of feathers behind the ear coverts. They tend to be solitary and carch insects on the wing, whistling as they feed. They lay 1 egg in a simple nest on the ground.
  Family Caprimulgidae - Nighthawks and Nightjars
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  76 species, 14 genera (Sibley and Monroe,1990), Dickinson (2003) and Harris (2009) include 89 species in 16 genera, and Clements (2007) lists 91 species. Harris (2009) suggests that the eared-nightjars might deserve separate family status. Sibley and Ahlquist (1990) group caprimulgids with owls into the Order Strigiformes. Worldwide in tropical and temperate regions apart from polar areas. Nighthawks are New World birds. Their closest relatives are probably swifts and owlet-nightjars - both groups eat whole prey.
   Caprimulgids are often referred to as "goatsuckers" (based on the mistaken belief that they suck milk from goats).
   Assuming the Eared-Nightjars are placed in a separate family (above), there are two subfamilies in the Caprimulgidae:
   Subfamily Chordeilinae - Nighthawks (10 species, 4 genera - New World only)
   Subfamily Caprimulginae - Typical Nightjars (66-76 species, 10 genera - worldwide)

   These are medium-sized, largely nocturnal birds with a large head and eyes placed on a short neck. They are small to medium-sized birds with a small and weak bill but the gape is deeply cleft. In nightjars, the gape is surrounded by large rictal bristles. The lower jaw opens both vertically and horizontally - in hot weather, they use gular flutter with their mouth open to dissipate heat. Their large eyes have a tapetum so their eyes shine if illuminated with a point source of light at night (during a trip to Sapelo, several of my students went hunting at night and were able to capture a Chuck-wills-widow by hand keeping it mesmerized with the light as they approached).
   Caprimultids have long wings and tail with relatively short legs and weak feet. However, they perch well and are able to walk a few steps.  Some perch along (rather than across) branches for concealment. The fourth toe has 4 phalanges and the hallux 2. The claw of the middle toe is usually pectinate. They are cryptically colored and their plumage is soft. Most species are sexually dimorphic with differences in coloration and the wing patterns and structure. There are no powder downs.
   Caprimulgids occur in a variety of habitats from sea level to timber line and from dense humid forests to semi-arid deserts.
   Most species are crepuscular or nocturnal. They are solitary and secretive. By day, they roost on ground or rocks, in litter, or on the ground. They roost with a horizontal rather than upright posture. Some species are more diurnal and may be more gregarious (especially some nighthawks). They generally feed from a perch - on the ground or low perch. A few feed on the ground. some hunt on foot. They eat a variety of smaller flies and termites to larger moths and other larger insects. One species eats Euphorbia flowers and small mice, another has been known to take small birds. They are the nocturnal equivalents of swifts and swallows. They swallow their prey whole. Nighthawks drink on the wing (scooping water from a puddle or lake) while nightjars generally depend on water in their food.
  Many species have complex, repetitive songs - often sung at dusk or dawn. Males in several species make mechanical sounds with their wings during courtship. Their flight itself, however, is generally silent. [Listen as you watch nighthawks over our dunes - you will hear a whirring sound as they wheel and dive in their displays.]
   Caprimulgids are generally monogamous (two are polygamous). Most are territorial. They do not build nests but place their 2 (1-3) eggs in a scrape or on leaves on the ground where they are incubated for 16-22 days. Chicks hatch asynchronously covered with down. The female broods and provided most of the parental care. They fly at about 20 days and are independent by 35 days. Some may lay a second clutch when the first is 2-3 weeks old (the male takes over care of the first brood).
   Some authorities suggest that nightjars will move their eggs or young when threatened by carrying them in their mouth. There is no real evidence, however, to support this belief.
   The Common Poorwill (below) is the only bird known to undergo a form of hibernation.
Eurasian Nightjar
Eurasian (European) Nightjar,
Caprimullgus europaeus.
Both images from Brehms Tierleben, 1892.
Nighthawk, Chordeiles.
    White-tailed Nightjar White-tailed Nightjar,
Caprimulgus cayennensis
Little Tobago/Bird of Paradise Island
Photo by Ed Konrad
                                    Wiki      ToL     EoL
    Hibernation and Hypothermy
       The Common Poorwill, Phalaenoptilus nuttalli, a western species, is the only bird known to hibernate. They roost in rock crevices in winter and their body temperature may decrease to 18-19° C (their normal body temperature is 40-42° C).                                                                                 Wiki
   Some birds, especially small hummingbirds, may become hypothermic at night to conserve energy, but rapidly regain normal temperatures during the day. Nestling swifts may also become hypothermic during periods of inclement weather when normal food supplies are not available. In winter, chickadees often roost in groups in a cavity where their body temperature may also drop on cold nights. Many smaller (less massive) birds probably have pronounced diurnal cycles in body temperature that is, to some degree, adaptive.
    Banner - Chuck-wills-widow. Privateer Road, Seabrook (Bob Hider)