Tree Swifts (Hemiprocnidae)

views updated

Tree swifts

(Hemiprocnidae)

Class Aves

Order Apodiformes

Suborder Apodi

Family Hemiprocnidae

Thumbnail description
Small to medium-sized birds with long, narrow, swept-back wings, deeply forked tail, and elaborate forehead crest or elongate feathered "whiskers"

Size
5.8–11.5 in (15–30 cm); 0.8–2.9 oz (21–79 g)

Number of genera, species
1 genus; 4 species

Habitat
Lowland forests and forest openings, river edges, and open grasslands and croplands where some trees remain

Conservation status
Not threatened

Distribution
Indian subcontinent, Indochina, Malay Peninsula, Indonesia, New Guinea, Bismarck, and Solomon Islands

Evolution and systematics

The tree swifts have always been recognized as separable from the other "true" swifts due to their brighter coloration, crest and whiskered ornamentation, and habit of perching and sally-flight foraging. Morphologically their wings do not show the extreme shortening of the humerus found in the swifts (Apodidae). Even so, the general resemblances between the swifts and tree swifts, backed up by skeletal anatomy and, more recently, DNA evidence, supports their being separate families within the suborder Apodi. The extinct fossil family Aegialornithidae from Europe is currently thought to be most closely related to the tree swifts and is sometimes considerd to be a subfamily of the Hemiprocnidae.

Physical characteristics

Tree swifts are truly flamboyant compared to swifts. Their brighter plumage with bright sheens to the blue and green coloration, chestnut facial patterns, along with their erectile forehead crests or elongate "whiskers" make them distinctive. Their long, narrow wings and deeply forked tails also serve to set them apart. Sexually dimorphic plumages are also not typical of the swifts. Tree swift chicks have natal down and a highly motted cryptic juvenal plumage.

Distribution

The crested tree swift (Hemiprocne coronata) has a widespread distribuution on the Indian subcontinent from the foothills of the Himalayas through much of peninsular India and Sri Lanka and southeast through Indochina, Cambodia, and Vietnam. The closely related gray-rumped tree swift (H. longipennis) replaces it in the Malay Peninsula and parts of Indonesia and broadly overlaps with the whiskered tree swift (H. comata). The moustached tree swift (H. mystacea) is found farthest east in eastern Indonesia, New Guinea, and the Bismarck and Solomon Islands.

Habitat

Although tree swifts forage widely over forested and savanna areas, they seem to prefer forest openings and edges and

river edges where the bare twigs of emergent trees provide suitable perches from which to make their dashing foraging flights. They are typically birds of lowland areas below 3,300 ft (1,000 m) but are occasionally recorded at higher elevations.

Behavior

Tree swifts are usually found singly or in pairs but some also occur in small groups of up to 10–12 individuals. They are not particulary gregarious and do not readily socialize with other tree swifts where their ranges overlap. They are quite vocal and have an array of harsh, rasping chatters and screams that are given both at rest and in flight. They have a characteristic upright stance when perched, with the crest, which is depressed in flight, usually erected. They are quick to use their flight skills in mobbing birds of prey.

Feeding ecology and diet

All dietary items are captured on the wing and presumably include an array of insects and possibly spiders. They feed most actively at dawn and dusk when loose flocks dash about at high speed.

Reproductive biology

The nests of tree swifts are among the most remarkable of birds. The tiny nest, barely large enough to hold the single white egg, is made of small chips of tree bark, feathers, and plant floss glued with salivary cement on the side of a narrow horizontal branch as much as 13–60 ft (4–18 m) above the ground. This most inconspicuous nest is difficult to detect and looks more like a slight natural knob on an othewise bare twig perch than a nest. Only careful observation of adults returning repeatedly to the same perch reveals the presence of a nest. The chick is equally cryptic in appearance with a lichen-like covering of natal down followed by the first contour plumage, characterized by broad mottled or whitish edges to the body feathers. This again makes the chick in its stationary upright resting posture strongly resemble a broken twig. The incubation period appears to be 21–26 days; the combined incubation and fledging period seems to be close to 50 days but detailed observations are lacking. Both sexes incubate and brood the chick, but females appear to spend more time in these activities.

Conservation status

Tree swifts can be found in suburban areas where suitable trees remain. However, their populations in some of these areas appear to be declining. The causes are unknown and no critical conservation issues have been identified.

Significance to humans

None known.

Species accounts

List of Species

Crested tree swift
Whiskered tree swift

Crested tree swift

Hemiprocne coronata

taxonomy

Hirundo coronata Tickell, 1833, Jungles of Borabhum and Dholbhum, India. Formerly considered conspecific with gray-rumped tree swift, Hemiprocne longipennis. Monotypic.

other common names

English: Indian tree swift; French: Hémiprocné courounné; German: Kronenbaumsegler; Spanish: Vencejo Arborícola Coronado.

physical characteristics

8.8 in (23 cm);0.7–1.0 oz (20–26g). Plumage largely blue-gray above with darker green-blue forehead crest and black eye patch and, in male, a reddish orange patch behind eye on ear coverts extending to side of throat. Throat and upper breast blue-gray; rest of undersides white. Wing feathers dark blackish brown and darker than body; tertials pale gray. Wings long and narrow, tail deeply forked.

distribution

From foothills of Himalayas and peninsular India, including Sri Lanka, east through Bangladesh to coastal areas of Thailand, Cambodia, and Vietnam. Replaced by gray-rumped tree swift in Malay Peninsula.

habitat

Forages over forested and open areas mostly at lower elevations. Prefers bare twigs on tops of emergent forest trees as perching site from which to forage.

behavior

Makes short swooping flights in search of aerial insects, often returning to original perch. Uses distinctive upright stance with erected crest when perched. Gives rasping calls when perched and in flight. Not particularly gregarious but may join others, particularly at roosts and during active feeding periods at dusk and dawn. Flight fast with much intermittent gliding in manner of bee-eaters or wood swallows.

feeding ecology and diet

Feeds on a presumably wide array of aerial insects gathered in flight.

reproductive biology

Builds tiny nest glued to small exposed horizontal branch typical of the family. The single egg takes 3+ weeks to hatch and incubation and fledging period combined takes approximately 50 days. The nest and chick are cryptically colored. The natal down of the chick is followed by a mottled cryptic contour plumage.

conservation status

No conservation issues identified.

significance to humans

None known.

Whiskered tree swift

Hemiprocne comata

taxonomy

Cypselus comatus Temminck, 1824, Sumatra. Two subspecies.

other common names

English: Lesser tree swift; French: Hémiprocné coiffé; German: Ohrenbaumsegler; Spanish: Vencejo Arborícola Chico.

physical characteristics

5.85 in (15 cm); 0.8–1.0 oz (21–26 g). Head and sides of throat glossy blue-black (with greenish gloss when fresh), body bronze olive, wing and tail dark. Short forehead crest and long lanceolate feathers in facial region forming two white stripes from lores over the eye to nape and from chin along jawline to side of neck. Ear coverts glossy blackish in females and rufous in males.

distribution

Peninsular Thailand and Malaysia, Sumatra, Borneo, and Philippines except Palawan.

habitat

Forages over canopy and edge areas of lowland forests. Utilizes midlevel bare twigs of forest trees as perches from which to make brief foraging flights.

behavior

Has characteristic upright stance when perched with short crest erected. Makes swooping flights in search of aerial prey, often returning to original perch. Appears to be territorial year-round only sharing foraging area with newly fledged young. Not as social as other tree swifts which may at times gather in larger groups. Utilizes lower perches than gray-rumped tree swift when inhabiting same area.

feeding ecology and diet

Feeds on presumably a large array of aerial insects taken on the wing.

reproductive biology

Makes tiny nest glued to horizontal branch characteristic of the family. The single white egg is incubated for about 21 days and the combined incubation and fledging period takes approximately 50 days.

conservation status

No conservation issues identified.

significance to humans

None known.

Resources

Books

Chantler, P. Swifts: A Guide to Swifts and Tree Swifts of the World. 2nd ed. New Haven: Yale University Press, 2000.

Coates, B. J. The Birds of Papua New Guinea. Vol. 1. Alderley, QLD: Dove Publishing Ltd., 1985.

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

Lowther, E. H. N. A Bird Photographer in India. London: Oxford University Press, 1949.

Wells, D. R. The Birds of the Thai-Malay Peninsula. Vol. 1. New York: Academic Press, 1999.