Brown Fish-Owl

识别特征

The brown fish owl has prominent ear tufts and rufous brown upperparts that are heavily streaked with black or dark brown. Its underparts are buffy-fulvous to whitish, with wavy dark brown streaks and finer brown barring. Its throat is white and conspicuously puffed. Its facial disk is indistinct, the bill dark and the iris golden yellow. Its featherless feet are yellow. Two-year old brown fish owls are somewhat paler than adults. Female and male differ slightly in size.<p>In body size, it ranges from 48 to 61 cm (19 to 24 in) with a wingspan from 125 to 140 cm (49 to 55 in). Its weight varies considerably, ranging from 1.1 to 2.5 kg (2.4 to 5.5 lb). Some of the variability is attributed to the range of sizes across the subspecies. Also, females are invariably at least somewhat larger than males and condition of birds is variable. It is slightly larger than the buffy fish owl with a darker brown hue.<p>Compared to eagle owls of similar length, fish owls tend to be even shorter in tail length and even heavier in build, have relatively larger wings, have considerably longer legs, and have a rough texture to the bottom of their toes. At least the latter two features are clear adaptations to aid these owls in capturing fish. Diurnal raptors who feed largely on fish have similar, if not identical, rough texture under their toes, which helps these birds grasp slippery fish. Unlike diurnal raptors who capture fish such as the osprey (Pandion haliaetus) as compared to most terrestrial raptors, the fish owls have large, powerful, and curved talons and a longitudinal sharp keel sitting under the middle claw with all having sharp cutting edges that are very much like those of eagle owls. Also, unlike fish-eating diurnal raptors will not submerge any part of their body while hunting, preferring only to put their feet into the water, although fish owls will hunt on foot, wading into the shallows. Unlike most owls, the feathers of fish owls are not soft to the touch and they lack the comb and hair-like fringes to the primaries, which allow other owls to fly silently in order to ambush their prey. Due to the lack of these feather-specializations, fish owl wing beats make sounds. The brown fish owl in particular is said to have a noisy wing beat, sometimes described as producing a singing sound, but another description claimed they could be "as silent as any other owl" in flight. The lack of a deep facial disc in fish owls is another indication of the unimportance of sound relative to vision in these owls, as facial disc depth (as well as inner ear size) are directly related to how important sound is to an owl's hunting behavior. Also different from most any other kind of owl, the bill is placed on the face between the eyes rather below it, which is said to impart this fish owl with a "remarkably morose and sinister expression". Similar adaptations, such as unwillingness to submerge beyond their legs and lack of sound-muffling feathers are also seen in the African fishing owls, which do not seem to be directly related. The brown fish owl has sometimes been regarded as conspecific with the Blakiston's fish owl (B. blakistoni), but there is an approximately 2,000 km (1,200 mi) gap in their distributions, not to mention a large number of physical differences not the least of which is the Blakiston's considerably greater size.

分类信息

The brown fish owl was formally described in 1788 by the German naturalist Johann Friedrich Gmelin in his revised and expanded edition of Carl Linnaeus's Systema Naturae. He placed it with the other owls in the genus Strix and coined the binomial name Strix zeylonensis. Gmelin based his description on the "Great Ceylonese horned owl" that had been described and illustrated by the naturalist Peter Brown in his book New Illustrations of Zoology. Joan Gideon Loten, an administrator in the Dutch East India Company had provided Brown with a picture of the owl that had been drawn by the Ceylonese artist Pieter Cornelis de Bevere. The brown fish owl is now placed in the genus Ketupa that was introduced in 1830 by the French naturalist René Lesson.<p>Four subspecies are recognised:<p>Results of a phylogenetic analysis of nine horned owl species indicate that Ketupa species form a monophyletic group.<p>In prehistoric times, this species may have been present across the central and eastern Mediterranean basin, in particular on islands. The Late Pleistocene Bubo insularis is typically considered to include the fragmentary remains originally described as Ophthalmomegas lamarmorae due to a mix-up with the fossil macaque Macaca majori and subsequently unstudied for many decades. Its fossil bones suggest a bird the size of a large spotted eagle-owl (B. africanus), a bit smaller still than the smallest living fish owls. It was certainly smallish but long-legged by eagle-owl standards, and its wing proportions differed conspicuously from a typical horned eagle owl. On the other hand, its leg and foot bones were more similar to those of a typical eagle-owl. Some consider it a specialized paleosubspecies of the brown fish owl that became extinct during the third Würm glaciation, while others reported remains of B. "insularis" in the Holocene of Sardinia and until the beginning of Roman Sardinia, with no subspecies being recognized.<p>The oldest remains date back at least to the Early Pliocene, about 5 million years ago. It was probably widely distributed around 120,000 years ago. After the onset of the last glacial period, less than 100,000 years ago, it disappeared from the western part of its range. The Late Miocene-Early Pliocene "Strix" perpasta is unlikely to belong in that genus, and also sometimes merged with B. insularis.

学名

Ketupa zeylonensis

命名信息

(Gmelin, JF, 1788)

目

Strigiformes

科

Strigidae

属

Ketupa

分布与栖息地

The brown fish owl is an all-year resident throughout most tropical and subtropical parts of the Indian Subcontinent to Southeast Asia and adjoining regions. West of its main range, it is patchily distributed to the Levant (possibly extinct) and southern Asia Minor (recently rediscovered). The typical habitat of brown fish owls is forest and woodland bordering streams, lakes or rice fields. It inhabits mainly the lowlands, from open woodland to dense forest as well as in plantations; in the Himalayas foothills it ranges into submontane forest up to 1,500 m (4,900 ft) above mean sea level or so but not higher. It frequently spends the day in stands of bamboo or other large shady trees. They be found around water reservoirs, along canals, on the outskirts of villages and along sea coasts. Western birds are found in semiarid landscape and may breed in oases in arid regions. Regardless of habitat, it rarely strays far from larger bodies of water such as rivers and lakes.Being a large predatory bird, the brown fish owl is only rarely found at a high population density, an exception being Sri Lanka, where this particular owl's adaptability to human habitat change has been beneficial in continued high numbers.

迁徙

Resident species

行为

Migration pattern: Resident species.

保护状况

Population trend: declining.

种群趋势

declining