Uditha Hettige - CBCN July 2007 page 121 to 124

In 2007 continuous observations were carried out on the Bay Owl of Sri Lanka Phodilus a. assimi­lis while nesting (Hettige 2007). It was the first time this had been done, and has significantly increased our knowl­edge of this bird.

One of the rar­est birds in the island (Henry 1998), its vocalization was discovered only in 2001 (Warakagoda & Gunawardena 2001), and prior to that there was no information on its behaviour in the wild.

Rasmussen deems the populations of the Bay Owl in Sri Lanka, known since the 19th century, and the Western Ghats P. a. rip­leyi, discovered in the mid-20th, together as a separate species, Ceylon Bay Owl, on the basis of the song of the island form (Rasmus­sen & Anderton 2005).

There were 12 records of P. a. assimi­lis before 2001 and seven more birds have been detected since (Ceylon Bird Club Notes [CBCN] 2003 July ff.).

The only previous knowledge of its nesting was from the collec­tion of three nestlings in the daytime once by vil­lagers (Phillips 1978). It was that: this owl nests in tree holes, its eggs number 3-4, and its breeding period includes November.

From analy­sis of data on nesting and singing we estima­te its breeding peri­ods to be: one about October to February, and another around mid-year, including July. Four more individuals had been heard singing in the last and first few months of the year, by the accounts of people liv­ing near forests, since 2001 (D Warakagoda, pers. comm.)

The recent nesting site was at Kudawa, by the 'Govi Sevana' road, in a for­ested area adjacent to the Sinharaja Reserve. A brief chronology of my observations and details further to those below are given in CBCN January 2007.

One of the pair of owls had been spotted on 17 January by Forest Department Guide Ranjith Premasiri. It had been roosting on a branch during the daytime, c. 5 m away from what was subsequently found to be the nest­ing tree, and c. 3 m above the ground, in a wooded area next to a Tea plantation. It was identified as a Bay Owl by Lester Perera, who was at Sinharaja that day.

When I reached the site the next evening a Bay Owl was perched on another tree in the vicinity, by the jeep track. We were surprised at the relatively open roost, as the species is known to be very elusive. We suspected that there would be some reason such as a nest near by.

Observations the same night revealed that the nesting tree was a dead Fish­tail Palm Caryota urens, and the nest-hole was a vertical hollow right at its broken top, c. 10 m above ground level.

As darkness fell the bird on the roost began moving to­wards the palm. Soon after it became quite dark it had come very close to the palm, moving from branch to branch of adjacent trees. It then slowly approached the nest, uttering a rather soft, short, squeaky note. A sec­ond owl called in a similar manner from within the hole, and kept calling. While the first bird ascended the palm it kept looking up towards the nest-hole. Eventually it went in. This took over 30 minutes from the time it began to move. The other bird may have had left the nest-hole when this one entered it, or, less probably, still been there. We could not see well enough in the dark to be certain.

For at least two days the same bird, presumably the male, roosted outside during the daytime, alone, about 5 m away from the nesting tree, and on rather or quite open perches c. 1.5 to 5 m above ground.

According to Thandula Jayarathna, a reliable observer at the site, the pattern of activity changed c. 18 days after this was first observed. Now both adults roosted outside continually, suggesting that the young had hatched and grown to a certain size. The pair were found to roost at distances varying from about 2 to 30 m apart from each other. At least one Bay Owl was seen at the site until at least 4 March, 47 days after one had been first seen here.

This suggests that the species roosts out in the open while nesting. The literature on records outside Sri Lanka states that it roosts in tree holes. That is presumably when it is not nesting.

The Bay Owl in Sri Lanka at its day roost tolerates human presence at much closer range than most species of the Strigidae, the other Family of owls, in Sri Lanka. This behaviour is also known in the south India population and the Oriental Bay Owl (Kannan 1993).

Of the birds captured in Sri Lanka, an adult was taken with the three nestlings. The above implies that all or some of the others also may have been taken from a day roost close to the nest.

Illustrations of the Bay Owl of Sri Lanka in the lit­erature, all of them showing it perched, depict its shape in varying ratios of height to width.

While roosting this owl, like all others, adopts a camouflage pose in 'alert mode' when a threat is detected in the vicinity. It does this by assuming a shape which disguises it as a broken branch or stump. The outline of the body is quickly changed from a somewhat plump to a slen­der shape. The change is effected by tightening of the body, or contour, feathers. (Warakagoda 2006.) Photographs taken by me at the Kudawa site show 'frozen' stages of this transformation in the present species. Some are reproduced here, in black-and-white, as a sequence.

This species, as all others in its Family, Tytonidae, lacks true ear-tufts. The formation of small 'pseudo-eartufts' in this bird, as in certain other owls, to enhance the effect described above, has been explained by Warakagoda (Koenig et al. 1998, Warakagoda 2006). This process, too, is seen in such photos taken at this site by others and myself.

No sexual dichromatism had been known in this owl. The pair observed at the nest site differed in appearance somewhat from each other, mainly in the density and distribution of dark spots on the underparts and the markings on the forehead and face. This may, however, be due to individual variability (Warakagoda, pers. comm.). It was photo-graphed and discerned by Kithsiri Gunawardena (Pers. comm.).

At night this bird perches comfortably on vertical stems of small trees in the forest, and rather low (Warakagoda & Gunawardena 2001, Sirivar­dana 2003), in the same manner as known in the Oriental Bay Owl P. badius. However, in the daytime it roosts on nearly or quite horizontal branches. This has been observed only in the pair above, but may be assumed is done generally, on the analogy of other owls.

A bird at this site when roosting outside the nest-hole in the daytime continually adjusted its position to face away from the sun. It did this by rotating the body a little from time to time, the feet being reposition­ed accordingly, and eventually turning through almost 180º.

How­ever, when danger approached the nest it looked intently at the intruder even turning around against the sun. While I was present this hap­pened with a Common Coucal Centropus sinensis, a Common Mynah Acrido­theres tris­tis and a Land Monitor lizard Varanus bengalensis.

Viewing the roosting birds in the daytime through 'optics', the follow­ing observa­tions were also made. Often a transparent or whitish liquid was present at the surface of the cornea of the eyes. Probing this liquid

Ceylon Bay Owl Phodilus assimilis assimilis 'Relaxed', plump shape and 'alert', slender shape with stages in change between these

at most times were Snipe-Flies of one or more species of the genus Chrysopilus (Family Rhagionidae) (Warakagoda, pers. com.) From time to time the bird covered its closed eyelids by moving over them a tuft of feathers adjacent to each eye from out- to inward. When the tuft was moved back outward the insects settled on this rather than remain nearer the source of the secretion. A few mos­quitoes were observed on the eyelids, less fre­quently (Warakagoda 2007).
   Such a phenomenon had not been known before in other owls in Sri Lanka, but was observed subsequently by Warakagoda in a photograph of a day-roosting Serendib Scops Owl Otus thilohoff­manni in February 2007 at Sinharaja, by Gunnar Patters­son (Warakagoda, pers. comm.)
   Four regurgitated pellets (the form in which undigested food material consumed is voided by owls) were collected at this site. They were ana­lyzed by me. Each of the four contained only bones and fur. All of these parts were of small rodents, averaging, with little variation, c. 10 cm in length (without tail). It was not possible for an expert to identify this fauna more exactly.
   None of the pellets contained skulls. Some had broken parts of skull bones and one had a lower jaw intact. In each pellet all other bones of the body that were found were intact. This suggests that the Bay Owl first crushes the head of a rodent and then swallows the animal whole. The procedure has been recorded before in the larger owls Sri Lanka.

Acknowledgements

   I am grateful to Messrs Deepal Warakagoda and 'U.S.' for helping to write this article, Lakshman Weeratunge, Entomologist of the National Museum, Colombo, for identifying the insects described above from pho-tographs, Sampath Goonatilake of IUCN Sri Lanka for identifying the prey fauna, and Mr K Gunawardena for sharing his photos and observa-tions and accompanying me in the field.
   My gratitude is due to Mr Ranjith Premasiri for informing me of the occurrence of the Bay Owl at the Sinharaja site, himself, Messrs E W Tila­kasiri, D Somapala and H Sunil of the Forest Department for infor­mation and assistance in the field, and especially Thandula Jayarathna of the Department for continuously providing the above, and for finding and providing the 'pellets'.
   For their company at the site I thank Messrs Palitha Antony, Chinthaka de Silva, Namal Kamalgoda, Amila Salgado and Niran Caldera.

References

Ceylon Bird Club Notes (2007) Ed. note in January issue
Gunawardena K (2007) Report in: Ceylon Bird Club Notes March
Henry G M (1998) A Guide to the Birds of Sri Lanka Third edition. KVG de Silva & Sons (Kandy), Kandy / Oxford University Press, New Delhi
Hettige U (2007) Report in: Ceylon Bird Club Notes January
Kannan R (1993) Rediscovery of the Oriental Bay Owl Phodilus badius in Peninsular India Forktail 8 Oriental Bird Club
Koenig C, Weick F & Becking J-H (1999) Owls: a Guide to the Owls of the World Yale Univer­sity Press, New Haven
Phillips W W A (1978) Annotated Checklist of the Birds of Ceylon (Sri Lanka) Revised edition. Wildlife & Nature Protection Society of Sri Lanka / Ceylon Bird Club, Colombo
Rasmussen P C & Anderton J C (2005) Birds of South Asia: the Ripley Guide Smithsonian Institution/Lynx Edicions, Washington DC/Barce­lona
Seneviratne S (2006) Report in: Ceylon Bird Club Notes February
Sirivardana U (2003) Report in: Ceylon Bird Club Notes July
Warakagoda D (2001, 2005, 2006, 2007) Reports in: Ceylon Bird Club Notes September, February, November, February
Warakagoda D & Gunawardena K (2001) Report in: Ceylon Bird Club Notes September.