Caprimulgiformes

(vertebrate zoology) An order of nocturnal and crepuscular birds, including nightjars, potoos, and frog-mouths.

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Family: Oilbirds
Family: Frogmouths
Family: Owlet-Nightjars
Family: Potoos
Family: Nightjars

(Nightjars)

Class: Aves

Order: Caprimulgiformes

Number of families: 5

Number of genera, species: 24 genera, 105 species

Evolution and systematics

Anatomical and biochemical data suggest owls (Strigiformes) are the closest relatives of the Caprimulgiformes, with swifts (Apodiformes) and trogons (Trogoniformes) as more distant relatives. The oldest fossils of Caprimulgiformes are from the Eocene to Oligocene around 55–35 million years ago (mya), by which time representatives of the oilbirds (Steatornithidae), owlet-nightjars (Aegothelidae), frogmouths (Podargidae), potoos (Nyctibiidae), and true nightjars (Caprimulgidae) had emerged, along with several species of the long-extinct caprimulgiform family Archaeotrogonidae.

Inferences from the fossil record coupled with evidence from rates of DNA evolution suggest the initial divergence of these families from a common ancestor of all Caprimulgiformes occurred between the end of the Cretaceous around 65 mya and the middle Eocene (50.5–42.0 mya). Eocene or Oligocene fossils of most of these caprimulgiform families are known from Europe (although owlet nightjars and oilbirds are only tentatively identified), pointing to much wider geographical ranges for many of them in the past than at present because modern oilbirds and potoos are exclusively South and Central American, modern frogmouths are restricted to Asia and Australasia, and modern owlet nightjars are found only in Australasia.

Some doubt remains about the sequence in which the five living families of Caprimulgiformes diverged from each other. Recognition of two suborders, Steatornithi for the oilbird and Caprimulgi for all the others, implies that the oilbirds were the oldest group to diverge and that the ecology (fruiteating) and behavior (echolocation) of the living oilbird are so unique that they easily suggest ancient origins. However, DNA-hybridization evidence and some anatomical features suggest the owlet nightjars diverged from an ancestral caprimulgiform stock earlier than the oilbirds, especially because owlet nightjars have several owl-like features, including a well-developed facial disk. The three remaining families, the frogmouths, potoos, and true nightjars are all well-defined groups but apparently rather closely interrelated. Two of these families are divided into subfamilies, the frogmouths into an Asian group (Batrachostominae) and an Australasian group (Podarginae), the true nightjars into nighthawks (Chordeilinae) and nightjars (Caprimulginae).

Physical characteristics

Caprimulgiformes are small to rather large nocturnal birds (0.7–23.6 oz; 20–670 g), all of which have relatively large heads with large eyes, a wide to very wide gape, and very short legs. The bill is small and weak in nightjars, nighthawks, and potoos; not much stronger in owlet nightjars; relatively strong in the oilbird; but stout and wide in the appropriately named frogmouths. Strong rictal bristles (specialized feathers with elongated, tapering shafts and sometimes short barbs that surround a bird's mouth) occur at the base of the bill in many of the species, often accompanied by other facial bristles. However, within the Caprimulgidae the absence of rictal bristles is the main character distinguishing the nighthawk subfamily Chordeilinae from the nightjars of the Caprimulginae; most potoos also lack rictal bristles. Many forest-living

Caprimulgiformes that feed by sallying from perches have short, rounded wings, but nightjars and nighthawks that feed in more sustained flights bear wings that are long and pointed, as does the strong-flying oilbird. The tail varies from short to long, with a rounded tip in most Caprimulgiformes but square or notched in some Caprimulgidae. Males of a few true nightjar species have wing feathers (innermost secondaries) or tail feathers that have been greatly modified as display plumes. Feet of Caprimulgiformes have four usually slender toes with the hallux (first toe) variously pointing forward, outward, or backward. A pectinate middle claw that is serrated or bears projections like the teeth of a comb occurs only in Caprimulgidae.

Like baby owls, Caprimulgiformes young hatch with a covering of soft down feathers. In the oilbirds, frogmouths, and owlet-nightjars, the first down is pale or white and succeeded by a second down plumage that is usually darker. In potoos and nightjars, however, the first down is often dark or patterned and is replaced directly by juvenal true feathers, which mainly resemble those of the adults in structure and coloration. Adult plumages of most species are marked in subdued shades of brown, gray, buff, rufous (rust-colored), or black, which provide beautifully elaborate concealing coloration. The wing and tail feathers are mainly dark or black, but in nightjars and nighthawks, signal markings are commonly hidden within them and consist of contrasting white, buff, or cinnamon patches that are revealed only when the wings or tail are spread.

Distribution

Caprimulgiformes are absent only from the Arctic, Antarctic, and sub-Antarctic and from most oceanic islands. They are most common in the tropics and subtropics, as expected for birds that mainly rely on large insect prey. Fossil records indicate the modern ranges of most of the families have contracted since the early Tertiary period, when subtropical forests were more widespread than today and included much of Europe and North America.

The oilbird has a modern range largely restricted to tropical South America; the potoos are also Neotropical with northern limits in Mexico, Hispaniola, and Jamaica and southern range limits in Uruguay. Owlet-nightjars have an Australasian range, from the northern Moluccas and New Guinea through Australia to Tasmania. The frogmouths include an Asian subfamily that ranges from southern India and Sri Lanka to Vietnam and southward to Java and the Philippines and an Australasian subfamily that ranges from New Guinea and the northern Solomon Islands through Australia to Tasmania. Only the Caprimulgidae has a nearly worldwide range, which spans from Canada to Argentina and northern Chile in the Americas; and, in the Old World, from Ireland, Scandinavia, and Siberia to South Africa, Sri Lanka, and through the East Indies to Australia and Tasmania, including most large islands. Of its two subfamilies, the Caprimulginae occupies almost all of this wide area, whereas the Chordeilinae are mainly American, with representatives that are tentatively classified alongside them from tropical Africa (brown night-jar Veles binotatus) and ranging from southern Asia to Australia (genus Eurostopodus).

Habitat

The ancestral habitat of Caprimulgiformes was apparently in tropical lowland forests, which still form the main habitat of the oilbird, owlet-nightjars, potoos, and frogmouths. At least a few of the species of the latter three families have extended into more open woodlands, savannas with trees, or scrub. Nevertheless, species of all these groups still rely heavily on trees, for food in the case of the oilbird and for perches and nest sites in the case of the others. Only the Caprimulgidae has occupied more open habitats, with many species inhabiting savannas and open woodlands, although some occupy grasslands or even semi-deserts and a few are restricted to closed forests.

Behavior

Although details of behavior of many of these secretive nocturnal birds are little known, at least one or a few species of each family have been studied sufficiently to allow generalizations that should apply more widely. Thus it is clear that most species are monogamous. The pair bond may be sustained with the birds living together in a territory for several years in succession (in tawny frogmouth Podargus strigoides) or the pairbond may be maintained only for one breeding season (European nightjar C. europaeus). Two African nightjars, in which the breeding males develop elaborate display plumes, are exceptional in being polygynous (mating with more than one female) (standard-winged nightjar Macrodipteryx longipennis, pennant-winged nightjar M. vexillarius). With these two species, the displaying males are visited by females to mate, after which the female alone is responsible for nesting and care of the young. A similar system apparently prevails with three South American nightjars (genus Macropsalis), in which males have elaborately elongated tail feathers.

Just as darkness hinders human observers watching nocturnal birds, it also limits the scope for visual display and communication among the birds themselves. Many Caprimulgiformes have therefore developed white or pale patches that can be exposed as effective signals in low light; these signal markings are often surrounded or contrasted with darker areas similar to the bold coloration in the American striped skunk (Mephitis mephitis). Movement also emphasizes the signal markings, such as when the bold white patches in the outer primaries and on outer tail feathers of male European nightjars are shown off in territorial display flights and their bold white throat patches are exposed as the head is lifted to give territorial songs. However, all these conspicuous markings can be hidden from predators during the day.

Sounds are much more effective than vision for communication at night, therefore it is perhaps unsurprising that many Caprimulgiformes appear to lack elaborate visual displays and to rely instead on vocalizations. Indeed, so far as known, all caprimulgiform species give distinctive calls or songs. In many cases, these provide the best means of detecting the birds' presence, and many are among the most beautiful, unusual, and distinctive of all bird sounds (e.g., the call giving rise to the mnemonic "Good Lord deliver us" of the African fiery-necked nightjar C. pectoralis); many are also well-known to local people (e.g., the onomatopeic, echoing, calls of the whip-poor-will C. vociferus). However, a few are monotonous drumming or hammering sounds (e.g., the monotonously repeated t-chop, t-chop, t-chop of the large-tailed nightjar C. macrurus) while a few are harsh or raucous (e.g., the loud guttural snoring of the great potoo Nyctibius grandis).

The nocturnal calls of many Caprimulgiformes undoubtedly function in advertisement or defense of territories because playback of recordings commonly results in a "song-duel" that may be accompanied or followed by rapid approach and aggressive displays. Tawny frogmouths are known to spend the whole year as pairs in well-defended territories, whereas some nightjars only advertise and defend territories for the duration of one breeding attempt. The territories of these birds not only provide much or all of the food for their owners, they also provide nesting and roosting sites, and presumably freedom from interference by conspecifics that might include illicit mating attempts. A few species are known to have territories of much more restricted extent, reduced in the colonial-nesting oilbird to the immediate vicinity of the nest. Since up to 10 male standard-winged nightjars may assemble to sing and display at a lek, which is visited by females, the territory in this species also must presumably be greatly reduced or absent.

The frogmouths, owlet-nightjars, and potoos that live year-round in the same territory appear to be among the most sedentary of all birds, with few or no records of extra-limital vagrancy. In contrast to these, some nightjars and nighthawks are long-distance migrants, and many others make shorter seasonal movements. Extreme examples of long-distance migration are provided by the European nightjar, which breeds widely across Europe and Siberia but vacates all of this area to spend the northern winter in Africa south of the Sahara, and the common nighthawk (Chordeiles minor), which breeds widely in North America north to southern Canada and winters in South America south to northern Argentina. Among many examples of shorter migrations, one of the best understood is with the pennant-winged nightjar, which breeds in savannas of Africa south of the equator but migrates to spend the nonbreeding season in the savannas north of the equator. Others, such as the standard-winged nightjar, move seasonally from one vegetation zone to another.

Resources

del Hoyo, J., A. Elliott, and J. Sargatal, eds. Handbook of Birds of the World. Vol. 5, Barn Owls to Hummingbirds Barcelona: Lynx Edicions, 1999.

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

"Caprimulgiformes." 0. Chaffee Zoological Gardens of Fresno, California. Jan. 2002 (24 Jan. 2002). "A Goat WHAT?!?" Mecklenburg Audubon, Charlotte, North Carolina. Jan. 2002 (24 Jan. 2002).

[Article by: David T. Holyoak, PhD]

An order of crepuscular or mainly nocturnal birds collectively known as the goatsuckers. The group is apparently most closely related to the owls (Strigiformes) and is found worldwide, mainly in the tropics and warm temperate regions. Species breeding in the Arctic and cooler temperate regions are migratory. See also Strigiformes.

The order Caprimulgiformes is divided into the suborder Steatornithes, containing the single family Steatornithidae (oilbirds; 1 species), and the suborder Caprimulgi, including the families Podargidae (frogmouths; 13 species), Aegothelidae (owlet-frogmouths; 8 species), Nyctibiidae (potoos; 6 species), and Caprimulgidae (nightjars or goatsuckers; 77 species). The largest family, Caprimulgidae, is found worldwide; Steatornithidae are restricted to northern South America; Podargidae live in the Old World tropics from India to Australia; Aegothelidae are restricted to Australia and surrounding islands; and Nyctibiidae are found in the New World tropics.

The goatsuckers are primarily insectivorous, although the large frogmouths also feed on small vertebrates; the oilbird is unique in feeding on fruits, especially of palms. Goatsuckers have a huge, generally weak mouth with long, stout bristles surrounding it to make an effective trap for insects caught in flight. The wings are well developed, but the feet are weak and serve mainly for perching. The plumage is soft and fluffy, and is mottled and barred brown and gray, serving as a cryptic protective coloration. White patches may exist on the wings, tail, and throat, which are visible only in flight. Goatsuckers are solitary but may migrate in loose flocks (nighthawks). Most species are highly vocal, using the calls to attract mates and defend territories. The English names of a number of species, such as the whippoorwill and chuck-will's-widow, are based on their calls. Goatsuckers nest on the ground or in trees, laying one to five eggs. Young are downy and remain in the nest until they are able to fly. A few species are known to hibernate.

The oilbirds are colonial nesters, placing their nest of seeds and droppings on ledges deep in caves. Paired adults remain together throughout the year, roosting on their breeding ledge. Oilbirds have excellent night vision, but inside their often totally dark caves they find their way by using echolocation based on pulses of sound of about 7000 Hz which are audible to the human ear. See also Aves; Echolocation.

The noun has one meaning:

Meaning #1: goatsuckers; frogmouths; oilbirds
  Synonym: order Caprimulgiformes

Caprimulgiformes
Large-tailed Nightjar, Caprimulgus macrurus
Scientific classification
Kingdom: Animalia Phylum: Chordata Class: Aves (unranked) Cypselomorphae Order: Caprimulgiformes Ridgway, 1881
Families
see text

The Caprimulgiformes is an order of birds that includes a number of birds with global distribution (except Antarctica). They are generally insectivorous and nocturnal. The order gets its name from the Latin for "goat-sucker", an old name based on an erroneous view of the European Nightjar's feeding habits.

Systematics

The classification of the various birds that make up the order has long been controversial and difficult, particularly in the case of the nightjars. All things considered, the nightjar order would probably best be limited to potoos, nightjars, and eared-nightjars, all other lineages being elevated to order level, and the owlet-nightjars being altogether distant:

• Family Steatornithidae (Oilbird) - probably distinct order N.N. ("Steatornithiformes"^[1])
• Family Podargidae (frogmouths, 12 species in 2 genera) - probably distinct order Podargiformes

• Family Nyctibiidae (Potoos, about 5 species in 1 genus)
• Family Caprimulgidae
  • Subfamily Chordeilinae (New World nighthawks)
  • Subfamily Caprimulginae (typical nightjars)
• Family Eurostopodidae (eared-nightjars)

Traditionally, they were regarded, on morphological grounds, as being midway between the owls (Strigiformes) and the swifts. Like the owls, they are nocturnal hunters with a highly developed sense of sight, and like the swifts they are excellent flyers with small, weak legs. At one time or another, they have allied with owls, swifts, kingfishers, hoopoes, mousebirds, hornbills, rollers, bee-eaters, woodpeckers, trogons and hummingbirds.

Based on analysis of sequence data - notably β-fibrinogen intron 7 -, Fain & Houde (2004) considered the families of the Caprimulgiformes to be members of the proposed clade Metaves, which also includes the hoatzin, tropicbirds, sandgrouse, pigeons, kagu, sunbittern, mesites, flamingos, grebes and swifts and hummingbirds. This clade was also found by the expanded study of Ericson et al. (2006), but support was extremely weak.

While only the latter study recovered monophyly of the Cypselomorphae (see below) within Metaves, the former was based on only a single locus and could not resolve their relationships according to standard criteria of statistical confidence. No morphological synapomorphies have been found that uniquely unite Metaves (or Caprimulgiformes for that matter), but numerous unlinked nuclear genes independently support their monophyly either in majority or whole. Ericson et al. (2006) concluded that if valid, the "Metaves" must originate quite some time before the Paleogene, and they reconciled this with the fossil record.

While the relationships of cypselomorphs are a subject of ongoing debate, the phylogeny of the individual lineages is better resolved. Much of the remaining uncertainty regards minor details.

Initial mtDNA cytochrome b sequence analysis (Mariaux & Braun 1996) agreed with earlier morphological (Cracraft 1981) and DNA-DNA hybridization (Sibley & Ahlquist 1990) studies insofar as that the oilbird and the frogmouths seemed rather distinct. The other lineages appeared to form a clade, but this is now known to have been caused by methodological limitiations.

The Aegothelidae (owlet-nightjars) with about a dozen living species in one genus are apparently closer to the Apodiformes (Mayr 2002); these and the Caprimulgiformes are closely related, being grouped together as Cypselomorphae. The oilbird and the frogmouths seem quite distinct among the remaining Caprimulgiformes, but their exact placement cannot be resolved based on osteological data alone (Mary 2002).

Even the study of Ericson et al. could not properly resolve the oilbird's and frogmouths' relationships beyond the fact that they are quite certainly well distinct. It robustly supported, however, the idea that the owlet-nightjars should be considered closer to Caprimulgiformes, unlike the methodologically weaker studies of Mariaux & Braun (1996) and Fain & Houde (2004).

Alternatively, Mayr's phylogenetic taxon Cypselomorphae might be placed at order rank and substitute the two present orders Caprimulgiformes and Apodiformes. Such a group would be fairly uninformative as regards its evolutionary history, as it has to include some very plesiomorphic and some extremely derived lineages (such as hummingbirds) to achieve monophyly.

Evolution

The fossil record of caprimulgiform birds (in the loose sense) is rather scant. Nonetheless, it supports the emerging consensus phylogeny well. The genus Paraprefica, probably from the Early Eocene (though this is somewhat uncertain), seems to be a basal form that at times has been allied with the oilbird and the potoos, but cannot be assigned to either with certainty. In the consensus scenario, it would represent a record of the initial divergence of the three lineages.

This nicely agrees with fossils suggesting that the basal divergence of the owlet-nightjar and apodiform branch also occurred during that time. In addition, Eocypselus, a Late Paleocene or Early Eocene genus of north-central Europe, cannot be assigned to any one cypselomorph lineage with certainty but appears to be some ancestral form.

These Paleogene birds strongly suggest that the 2 main extant lineages of cypselomorphs separated about 60-55 mya (Selandian-Thanetian), and that some time around the Lutetian-Bartonian boundary, some 40 mya, the common ancestors of Nyctibiidae, Caprimulgidae and Eurostopodidae diverged from those of oilbird and frogmouths.

References

Wikimedia Commons has media related to:

Caprimulgiformes

• Cracraft, Joel (1981): Toward a phylogenetic classification of the recent birds of the world (Class Aves). Auk 98(4): 681–714. PDF fulltext
• Ericson, Per G.P.; Anderson, Cajsa L.; Britton, Tom; Elżanowski, Andrzej; Johansson, Ulf S. ; Källersjö, Mari; Ohlson, Jan I.; Parsons, Thomas J.; Zuccon, Dario & Mayr, Gerald (2006): Diversification of Neoaves: integration of molecular sequence data and fossils. Biol. Lett. 2(4): 543-547. doi:10.1098/rsbl.2006.0523 PDF fulltext
• Fain, Matthew G. & Houde, Peter (2004): Parallel radiations in the primary clades of birds. Evolution 58(11): 2558-2573. doi:10.1554/04-235 PDF fulltext
• Mayr, Gerald (2002): Osteological evidence for paraphyly of the avian order Caprimulgiformes (nightjars and allies). Journal für Ornithologie 143(1): 82–97. doi:10.1046/j.1439-0361.2002.01030.x HTML abstract
• Mariaux, Jean & Braun, Michael J. (1996): A Molecular Phylogenetic Survey of the Nightjars and Allies (Caprimulgiformes) with Special Emphasis on the Potoos (Nyctibiidae). Molecular Phylogenetics and Evolution 6(2): 228–244. doi:10.1006/mpev.1996.0073 (HTML abstract)
• Sibley, Charles Gald & Ahlquist, Jon Edward (1990): Phylogeny and classification of birds. Yale University Press, New Haven, Conn.

Footnotes

1. ^ Apparently not a valid taxon (yet), and thus it must not be written without quotation marks.

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