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Treeswifts (family Hemiprocnidae) is allied to swifts but they differ in a number of important ways such as their non-reversible hind toe that enable them to perch and colourful markings in their passerine-like plumage. Aside from the Whiskered Treeswift, there are only four other species of treeswift: Grey-rumped Treeswift, Crested Treeswift and Moustached Treeswift. Their distribution ranged from the Indian subcontinent to Southeast Asia and Papua New Guinea.
The Whiskered Treeswift is a small bird about 15 cm in length, with relatively long wings that when folded, it crossed each other and extend beyond the tail. It has a blackish head with very short erectile crest, two distinct white stripes or “whiskers” above and below the eye and a small black bill. It is olive-grey below grading into white lower belly and undertail covert. The wing is glossy bluish-black and the tail is deeply forked. The male differ from female by having chestnut ear covert.
The Whiskered Treeswift is noisy at times, calling while perching or flying. The call consists of a series of high pitched squeaky notes that resemble the sound produced by rubber toy.
Habitat and Distribution
The Whiskered Treeswift is found in Southeast Asia including Thailand, Peninsular Malaysia, Borneo and the Philippines. It prefers rainforest habitat, where it frequents forest edges and openings, and nearby wooded areas.
Like swifts, the Whiskered Treeswift feeds on aerial insects above the forest canopy that they catch on the wing. It is commonly seen flying in broad circles together with different species of swift. They also sally out to catch flying insects from a high perch, and often return to the same perch like a bee-eater.
The closely related Grey-rumped Treeswift bear close resemblance to the Whiskered Treeswift but it lacks the distinct face marking of the latter species, and it is the most likely treeswift observed far from forested areas, unlike the Whiskered Treeswift that confined to the rainforest and the immediate vicinity.
Because the Whiskered Treeswift mixes with swifts during its aerial foraging bouts, it is confusable with several species of swifts. But in flight, the Whiskered Treeswift has longer wings and deeply forked tail. The forked tail is frequently contracted while flying and tapering toward the tip. In addition, swifts do not perch erect like treeswifts, instead they cling on vertical surface.
The nesting behavior of the Whiskered Treeswift is one of the interesting aspect of its life history. Similar to swift, the nest is made mainly of saliva and feathers, but the Whiskered Treeswift build its nest on twigs of tall trees; nothing like the swifts that prefer to nest in man-made structures like under bridges, and on cliff and cave walls. The nest is crescent shape and it is so small that it barely enough to support a nestling. It is difficult to spot the nest even as it is attached to a twig with a diameter as small as a pencil. Nonetheless, this could be advantageous to the bird since it make difficult for predators to see the nest.
The female lays only one egg that is white in colour, and the male and female take turn to incubate the egg which takes around 3 weeks. Several weeks after the egg hatched, the chick fledges but it stays close within the parent territory where it is still tended by its parent. Juvenile looks like adult but it has shorter whiskers and mottled breast.
The Whiskered Treeswift is one of the interesting and fairly common forest birds of Southeast Asia. They are quite conspicuous in forest parks since they like to perch in tall trees fringing the main entrance, parking lots and camping sites. Furthermore, the Whiskered Treeswift are quite approachable, active and delightful to watch, thus they should be one of the highlights of birdwatching in the region.