Deepal Warakagoda

In December 2005, eighteen months after the type description of the Serendib Scops Owl Otus thilohoffmanni was published (Warakagoda & Rasmussen 2004), for the first time I had the opportunity to make a lengthy observation of the species at its day roost. In this and many subse­quent observations (e.g. Warakagoda 2005, 2006a, 2006b) it was possible to study aspects of its appearance in this condition.

It is normal behaviour for all owls and other nocturnal birds to adopt a camouflage pose while roosting in the daytime when threat or danger is detected in the vicinity.

An owl, in changing to this 'alert mode', 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 more slender appearance.
At the same time, groups of feathers in the facial disk, fore­head and crown are adjusted to give the appearance of the top of such a branch.

Certain species of owls possess two elongated ear-tufts which are sepa­rate from the other feathers of the head. In the bird's 'relaxed mode' the tufts lie nearly flat on the forehead or sides of the head - though visi­ble as separate entities. In the 'alert mode', to enhance the camouflage effect, such a bird erects these long tufts to be very prominent - a famil­iar sight to those who have studied owls.

Examples of such species in Sri Lanka are: amongst small owls, the Indian Scops Owl O. bakkamoena (found in home gardens) and Little Scops Owl O. sunia (a forest bird) and, amongst large owls, the Brown Fish Owl Ketupa zeylon­ensis (rather common) and Forest Eagle-Owl Bubo nipalensis (a rather uncommon forest species).

The Serendib Scops Owl lacks this feature of separate, 'true' ear-tufts. It is one of the very few such species amongst the scops owls of the world. The males and females of the species I had examined in hand, and all but one of the many individuals observed at night, showed no existence of ear-tufts.

The one excep­tion had been a male seen at very close range at night that appeared to briefly dis­play such entities. Later, in a lengthy obser­vation of the same individual at night, from some distance away and several different angles, chiefly in order to investigate this very feature, no eartuft-like entities were visible. Both these records were in early 2002.

Surprisingly, however, individuals of the new owl observed at daytime roosts consistently showed two small, eartuft-like protrusions. These are much shorter and less prominent than the erected ear-tufts of the familar and similar-sized Indian Scops Owl, but still quite distinct.

During many observations since December 2005 of the Ser­endib at day­time roosts I studied the way this species acquires an appear­ance which includes erected ear-tufts as a postural feature when ear-tufts are absent as an anatomical feature. The study was greatly aided by many excellent photographs at day roosts and nighttime perches taken by Uditha Hettige.
In the 'alert mode' of the Serendib in daytime the following happens, in addition to the narrowing of the body in the normal manner of owls.

Certain feather groups on the forehead, fore-crown, and sides of the facial disk are compressed and flattened. Feather tracts of the fore­head at the edges of the disk over the inward part of the eyes are folded. This makes the top left and right edges of the disk stand out. The edges are supported also by adjacent feather groups on the crown being partly or fully raised. The impression of short ear-tufts is created in this manner.

Another result of these changes is an obvious, broader and deeper 'V' on the forehead, showing up more white, than in a bird in 'relaxed mode'. This is formed by the lowered edges of the upper central part of the facial disk, and the white is in the basal part of the spread feathers in the 'V'.

A few of the relevant observations are reported in the Ceylon Bird Club Notes (Warakagoda 2005, 2006a). Of one occasion I wrote: 'At our close approach this bird also acquired the shape showing small eartuft-like pro­trusions on its head. We removed ourselves from its vicinity and left it alone for some time. Then I quietly observed it from a distance through binoculars. It had assumed its normal, 'earless' look.' (Waraka­goda 2006a.)

At night the Serendib 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.

A fully-fledged juvenile, observed and photographed in April 2006, also dis­played this postural feature, by erecting a few feathers on the sides of the crown, without a contribution from the feathers of the facial disk, as the disk was not yet well developed.

I have also observed, on two occasions, the Ceylon Bay Owl Phodilus assimilis, at night and in close proximity to me, adopting a similar pos­tural feature of short 'pseudo-eartufts'. This was effected by elongating its facial disk vertically, folding the edges of the sides of the disk, and broadening the 'V' shape on the forehead. The species belongs to a sepa­rate Family of owls in which none have true ear-tufts as an anatomi­cal feature.

It is a well-known fact that in similar situations other species of owls lacking true ear-tufts adopt a camouflage pose which gives the impres­sion of small ear-tufts. (See König et al. 1999.)

Acknowledgments

I thank Mr Uditha Hettige for his photography, Dr Pamela Rasmussen and Dr Senaka Abeyratne for comments on the 'pseudo-eartufts', and 'U.S.' for assisting in this article.

References

König C, Weick F & Becking J-H (1999) Owls. A guide to the owls of the world. Yale Univer­sity Press, New Haven. P.28

Rasmussen P C & Anderton J C (2005) Birds of South Asia. The Ripley Guide. Vols.1-2. Smithsonian Institution & Lynx Edicions, Washington DC & Barce­lona

Warakagoda D H & Rasmussen P C (2004) A new species of scops-owl from Sri Lanka. Bull. Brit. Orn. Club 124(2). P.85-105

Warakagoda D (2005) In: Ceylon Bird Club Notes December. P.148-149

Warakagoda D (2006) In: Ceylon Bird Club Notes January. P.5

Warakagoda D (In press) Sri Lanka's Serendib Scops Owl BirdingASIA No.6.