Friday, September 16, 2011

Paduwan Bassa - Serendib Scops Owl (Otus thilohoffmanni)


The new species is a small scops owl about 17 cm in length, with a short tail, and almost uniformly rufescent upperparts but for the presence of small black spots all over the body. The face is a little darker, and underparts paler than upper parts, with the belly becoming whitish. It has no distinct, “true” ear-tufts, but see below. The irides are orange-yellow in the male and yellow in the female and juvenile. The beak, legs and claws are whitish. The legs are feathered on the tibia and upper tarsi. The vocalization comprises a single note, pu’u’u, repeated at long intervals. Male and female call in the same pattern but in different keys.


At the time of the type description we knew that birds of a pair roosted fairly close together or well apart within their territory. Later we learnt that in some pairs the birds roost together or very close. A fledgling has been observed roosting with an adult male. Roosting height varies from about 1 to 2.5 m. A well-concealed place is chosen in dense vegetation in the undergrowth or just above it. Here the bird sits on an almost or entirely horizontal twig, usually close to dead leaves. Its size, shape and coloration blend it in perfectly with the surroundings, making it hard to detect. When an owl is in “alert mode” at its daytime roost, in reaction to possible danger in the vicinity, it quickly adopts a stance which disguises it as a short, upright, broken branch. It tightens body feathers, which are otherwise loose and relaxed, to acquire a narrower appearance. At the same time it adjusts the feathers of the facial disk, forehead and crown to give the appearance of the top of such a branch. This latter arrangement is adopted also by species of owl which have two obvious, separate ear-tufts, which are erected to enhance this effect. The Serendib Scops Owl, which does not possess ear-tufts, achieves a similar effect by compressing and flattening feathers on the forehead, forecrown and sides of the facial disk, and folding feather tracts on the forehead at the edges of the disk over the inner part of the eyes. This makes the top left and right edges of the disk stand out, with also the support of adjacent crown feathers, giving an impression of short ear-tufts. Another result is an obvious, broader and deeper V on the forehead, showing up more white, than in a bird in “relaxed mode”. At night the Serendib Scops Owl adopts this “pseudo-eartuft” arrangement only very rarely, according to our observations, probably because there is no significant advantage of such visual camouflage in the dark. It has been known that in similar situations species of owls lacking true ear-tufts adopt a camouflage pose which suggests the presence of small ear-tufts.


Endemic to Sri Lanka, found thus far only in the southwest quarter of the island at Kitulgala, Kanneliya and Eratna-Gilimale Reserves, with its strongholds in the Sinharaja and Morapitiya-Runakanda reserves, which are contiguous.


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