Brown Fish Owl
Order: Strigiformes
Family: Strigidae
Genus/Species: Ketupa zeylonensis
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| Photo by Kate Volz, NZP |
Description
The Brown Fish Owl of southeast Asia is similar in appearance to the familiar Great Horned Owl (Bubo virginianus), its closest relative in North America. Both species are characterized by large size, cryptic coloration and prominent ear tufts. The Brown Fish Owl (50-57 cm, 1100 g) is mottled in brown and buff on the back, head and wings with buffy-white streaked underparts. Their white throats visibly inflate when they produce the deep, booming "hoom-hoom" calls of their duets. A closer inspection of the Brown Fish Owl will reveal specialized traits that set it apart from most other owls in its family.
Fish owls of the genus Ketupa have no feathers on their lower legs and feet to get wet when they snatch prey from surface of the water. The soles of their feet have specialized spiny scales called spicules that enable them to grip slippery aquatic prey securely. Most owls have a short comb-like fringe on the forward edge of their outer flight feathers. This fringe is believed to reduce the sound created by flapping wings. Silent flight allows typical owls to approach their prey without being heard. Fish owls lack this fringe structure on their primaries. A silent approach may be less important to an owl hunting underwater prey.
One of the most obvious characteristics of the owl family is the facial disc, a specialized arrangement of facial feathers under muscular control. An owl can change the shape of its facial discs to locate and channel sound in much the same way that a deer will rotate its large external ears. These facial discs are less well-developed in the fish owls than in their closest relatives. This may indicate that they hunt more by sight than sound. The reduced facial disc has the cosmetic effect of giving them a somewhat low-browed sinister appearance when compared to the Great Horned Owl.
Distribution and Habitat
The Brown Fish Owl's historic range extended from the Middle East in southern Turkey, Israel and northern Syria eastward to southern China, and south from the Himalayas into Malaysia and Sri Lanka. Though the Brown Fish Owl is still common in Sri Lanka, it has become rare in most other portions of its range.
They are found in a wide varieties of forest habitats in close proximity to fresh, slow-moving water. They will utilize agricultural lands if they include clumps of large trees. They are found from coastal lowlands to altitudes of 1500 m.
Diet
Fish owls swoop down from exposed perches or large rocks to snatch prey from the surface or just below the surface of the water. They also wade in shallow water in search of prey. From three to thirteen hours after consuming a meal, the owl's muscular stomach will compress the undigestible hair, bones, feathers, exoskeletons etc... into a compact pellet which is regurgitated. Examination of these "owl pellets" allows naturalists to accurately catalog an individual owl's diet. The diet of this species includes fish, frogs, freshwater Potamon crabs, crayfish, lizards, snakes, water beetles and other insects. They will occasionally consume ducks, herons, and bats.
Reproduction
Brown Fish Owls generally breed in the dry seasons when lower water levels make aquatic prey more accessible. Nests are located in natural tree hollows, large forks in trees, old raptor nests, on rock ledges or even on ruins of buildings. They are generally well off the ground (4-21 m) and close to water. The female lays two eggs which she incubates alone for 34-38 days. The young fledge at 51 days.
Conservation
The recent range of the Brown Fish Owl was divided into two disjunct populations. The Middle East population occupied a small area from southern Turkey to Syria, Israel and Iraq. The Brown Fish Owl was driven to extinction in Israel in the 1950s by the wide spread use of the poison thallium sulfate to control rodents. It is believed to be gone from Iraq as well. The owl is increasingly rare in Syria and Turkey. The last confirmed sighting in Turkey was in 1990.
The larger portion of the population ranged from southern Iran and Pakistan east to China. It is now gone from Iran and very rare in Pakistan. The Brown Fish Owl remains one of the commonest owls in Sri Lanka and is not considered threatened as a species. It is listed on CITES II. The closely related Blakiston's Eagle-Owl, Bubo blakistoni, was once considered to be a subspecies of the Brown Fish Owl. Blakiston's Eagle-owl, listed as endangered, is one of the rarest species of owl in the world.
References
Marks, J.S., Cannings, R.J. and H. Mikkola. (1999). Family Strigidae (Typical Owls). Pp. 76-151 in: del Hoyo, J., Elliot, A. and J. Sargatal. eds. (1999). Handbook of the Birds of the World. Vol. 5. Barn-owls to Hummingbirds. Lynx Edicions, Barcelona.
Voous, K.H. 1988. Owls of the Northern Hemisphere. William
Collins Sons and Co. Ltd. London.
Please note: There are no longer any of these birds at the Zoo.
