Owlet-Nightjars (Aegothelidae)

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Owlet-nightjars

(Aegothelidae)

Class Aves

Order Caprimulgiformes

Suborder Caprimulgi

Family Aegothelidae

Thumbnail description
Small to medium-sized, cryptically colored nocturnal birds that perch upright; have large heads, large forward-facing eyes within a facial disk, rounded wings, small legs and feet, and long toes that bear long claws

Size
7–12 in (18–30 cm); 1.0–3.5 oz (29–98 g)

Number of genera, species
1 genus; 7 species

Habitat
Forest, woodlands, scrub, and savannas

Conservation status
Critically Endangered: 1 species

Distribution
Northern Moluccas, New Guinea and satellite islands, Australia, Tasmania, and New Caledonia

Evolution and systematics

Owlet-nightjars are the most distinctive group in the order Caprimulgiformes, showing characteristics that to some extent link this order with the owls (Strigiformes). Similarities between owlet-nightjars and owls include the facial disk with eyes directed forwards, hole nesting, unmarked white eggs, and certain anatomical features. Furthermore, DNA-hybridization studies point to early evolutionary divergence of owlet-nightjars from the other Caprimulgiformes, perhaps not long after the early ancestors of the order diverged from ancestral owls. The earliest fossil owlet-nightjars are known from the Upper Eocene, suggesting that the family evolved in the early Tertiary.

As of 2001, all living species of owlet-nightjars are placed in the genus Aegotheles. There is some uncertainty about how many species should be recognized, particularly about whether spangled owlet-nightjars (Aegotheles tatei) should be regarded as a distinct species or as a subspecies of feline owletnightjars (A. insignis). Further studies of these poorly known birds may also suggest that certain populations of other species that are currently regarded as subspecies might be better elevated to species rank.

Physical characteristics

Like other members of the Caprimulgiformes, owletnightjars have a relatively large head, large eyes, and a wide gape. The small hooked bill has a wide base. Rictal bristles (the rictus is the gape of a bird's mouth) are well developed at the base of the bill and these along with other whiskers (facial bristles) are thought to function in directing prey into the mouth and in protecting the eyes from hard insect prey; a tactile function has also been suggested. Flank feathers are elongated. The wings are rather long but rounded and the tail is moderately long and wedge shaped. The legs are relatively short, but less so than in most other Caprimulgiformes, and the toes are long, slender, and bear claws. Aegotheles novaezealandiae, a species known only by fossils from the Quaternary of New Zealand, had much larger feet and legs than any living species and reduced wings, suggesting that it was more terrestrial than any living species. The rare New Caledonian owlet-nightjar (A. savesi) has legs and wings that approach the rather strong legs and reduced wings of the extinct New Zealand form, suggesting that it may also have come to rely more on walking and less on flying than other owletnightjars, but the habits of the living bird are almost unknown.

The plumage coloration of owlet-nightjars consists of the beautifully marked shades of brown, gray, buff, rufous, and blackish that characterize the Caprimulgiformes and promote concealment from predators. Patterns of several species are dominated by fine dark barring whereas others have bold blotches or streaks, often with prominent facial stripes. Sexes are similar.

Distribution

Owlet-nightjars reach their greatest diversity in New Guinea, which has seven of the nine species. Among these are Archbold's (A. archboldi), barred (A. bennettii), and Wallace's (A. wallacii) owlet-nightjars, as well as a small population of the Australian owlet-nightjar (A. cristatus), which is the only species in Australia and Tasmania. The other two species are restricted to the Northern Moluccas (Moluccan owlet nightjar, A. crinifrons) or New Caledonia (New Caledonian owlet-nightjar). All species are sedentary, with movements apparently limited to local dispersal.

Habitat

Owlet-nightjars are mainly forest birds, with different species in New Guinea occurring in lowland rainforests, mid-mountain forests, or in montane forests up to the scrubby growths at the tree line. Only the Australian owlet-nightjar occurs extensively in more open habitats in addition to open forests and woodlands. They extend into scrub-covered country such as mallee in the Australian interior and into coastal mangroves and feed in grasslands that adjoin habitats with trees.

Behavior

Owlet-nightjars occupy concealed roosts during the day, commonly in holes in trees. Some species roost in the concealment

afforded by dense vines. Unless they are disturbed, all activity occurs in near-darkness between late dusk and the early predawn light. Flight is swift and direct but usually of short duration. Very little is known of the social organization and other aspects of behavior of most species. The broad outlines of behavior are clear only for the better-studied Australian owletnightjar. In that species, a pair of birds lives all year within a large territory. The pair roost in close proximity throughout the year, although roost sites are frequently changed.

Nocturnal calls provide the main evidence of the presence and identity of owlet nightjar species, and there can be little doubt that the voice is the main means by which these birds communicate with each other. Different species produce characteristic churring, snarling, or whistling sounds that evidently function in defense of territories. The full vocabulary is unknown for most species, but sounds given by some include hissing during threat displays from nest holes.

Feeding ecology and diet

The diet of most owlet-nightjars consists mainly of insects, supplemented by other small invertebrates such as spiders and millipedes. The mountain owlet-nightjar (A. albertisi) includes earthworms in its diet. The food of several species remains completely unknown. The main feeding technique consists of sallying from perches to capture prey in the bill, often from the ground, but also sometimes from tree trunks or by fluttering against foliage. Each prey item is swallowed whole.

Reproductive biology

For several species of owlet-nightjars, nests have not been discovered. All described nests have been in holes, mainly tree holes. Australian owlet-nightjars sometimes nest in cavities of banks or buildings. Clutches are of one to five, slightly glossy, unmarked white eggs that, for unknown reasons, have unusually thick shells. Young hatch with white down which is replaced by a second coat of gray down before the juvenal feathers grow. Details of breeding are known only for the Australian species, in which incubation takes 25–27 days and is carried out at least mainly by the female, eggs hatch over several days, the young are fed by both parents, and fledging occurs after 21–32 days. No nest cleaning occurs so that droppings accumulate in the nest cavity.

Conservation status

New Caledonian owlet-nightjars were known only from a single specimen collected in 1880, and they were feared extinct until a sighting was reported in 1998. It is now regarded as Critically Endangered. None of the other species is thought to be seriously threatened, although several of those in New Guinea remain poorly known and susceptible to deforestation.

Significance to humans

The owlet-nightjars are among the most inconspicuous and retiring of nocturnal forest birds; even local tribespeople in New Guinea know little about them.

Species accounts

List of Species

Feline owlet-nightjar
Mountain owlet-nightjar
Barred owlet-nightjar
Australian owlet-nightjar

Feline owlet-nightjar

Aegotheles insignis

taxonomy

Aegotheles insignis Salvadori, 1875, Hatam, Arfak Mountains, New Guinea. Monotypic.

other common names

English: Reddish or large owlet-nightjar; French: Grand égothèle; German: Käuzchenschwalm; Spanish: Egotelo grande.

physical characteristics

12 in (30 cm); 2.1–3.5 oz (59–98 g). Two well-defined color morphs—rufous and brown; intermediates also occur. upperparts have sparse whitish streaks or spots and prominent lateral crown stripes; throat is buff or white; underparts have bold whitish spots. Sexes are similar.

distribution

New Guinea.

habitat

Montane forests.

behavior

Solitary, secretive, and little known.

feeding ecology and diet

Diet of insects, including beetles.

reproductive biology

Nest and eggs unknown.

conservation status

Not threatened.

significance to humans

None known.

Mountain owlet-nightjar

Aegotheles albertisi

taxonomy

Aegotheles albertisi Sclater, 1874, Arfak Mountains, New Guinea. Three subspecies.

other common names

French: Égothèle montagnard; German: Bergschwalm; Spanish: Egotelo montano.

physical characteristics

7–8 in (18–20 cm); 0.9–1.5 oz (25–43 g). Rufous and brown morphs; intermediates also occur. Sexes are similar.

distribution

New Guinea mountains.

habitat

Montane forests, extending to edges.

behavior

Secretive, nocturnal, roosting in hollows during day.

feeding ecology and diet

Catches food on ground beneath forest canopy and in clearings, taking insects and earthworms.

reproductive biology

Nests in hole in tree stump; clutch apparently a single white egg.

conservation status

Not threatened.

significance to humans

None known.

Barred owlet-nightjar

Aegotheles bennettii

taxonomy

Aegotheles bennettii Salvadori and D'Albertis, 1875, Hall Sound, New Guinea. Five subspecies.

other common names

English: Bennett's or collared owlet-nightjar; French: Égothèle de Bennett; German: Bennettschwalm; Spanish: Egotelo barrado.

physical characteristics

8–9 in (20–23 cm); 1.6–1.7 oz (45–47 g). Upperparts are dark brown to blackish with narrow light lines; underparts are pale gray to whitish buff with broad bars and spots. Sexes are similar.

distribution

New Guinea.

habitat

Lowland forests.

behavior

Little known; roosts by day in tree hollows.

feeding ecology and diet

Not known.

reproductive biology

Nest sites undescribed; eggs white.

conservation status

Not threatened.

significance to humans

None known.

Australian owlet-nightjar

Aegotheles cristatus

taxonomy

Caprimulgus cristatus Shaw Smith & Hunter, 1790, New South Wales. Two subspecies.

other common names

English: Owlet-nightjar, crested owlet-nightjar; French: Égothèle d'Australie; German: Baumschwalm; Spanish: Egotelo Australiano.

physical characteristics

8.3–10 in (21–25 cm); 1.4–2.1 oz (39–60 g). Upperparts are dark gray with pales lines and spots; underparts are paler with narrow brown lines. Sexes often similar but females vary between a gray morph and a rufous morph (with intermediates). The extreme rufous morph does not seem to occur in males, although intermediate males are known.

distribution

Australia, Tasmania, and southeastern New Guinea.

habitat

Open forests, woodlands, scrub, and mangroves.

behavior

Sedentary in pairs. Roosts by day, usually in tree holes.

feeding ecology and diet

Feeds mainly on insects, most of which are caught by swooping (sallying) to ground from low perch.

reproductive biology

Nests in hole, usually in tree. Clutches of two to five white eggs laid between August and December. Young hatch with white down which is replaced by gray down before juvenal feathers grow. Incubation period 25–27 days, fledging period usually 21–29 days.

conservation status

Not threatened, although suffers mortality from domestic cats and road kills.

significance to humans

Mentioned in the legends of aboriginal Australians.

Resources

Books

Holyoak, D.T. "Owlet-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.