Brown fish owl

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Brown fish owl
Brown fish owl in Biligiriranga Hills
Calls (South India)

Least Concern  (IUCN 3.1)[1]
CITES Appendix II (CITES)[1]
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Strigiformes
Family: Strigidae
Genus: Ketupa
Species:
K. zeylonensis
Binomial name
Ketupa zeylonensis
(Gmelin, JF, 1788)
Subspecies

See text

Range of brown fish owl
  Resident
  Possibly Extant (resident)
Synonyms
  • Bubo zeylonensis
  • Strix zeylonensis Gmelin, 1788

and see text

At Ranthambore National Park

The brown fish owl (Ketupa zeylonensis) is a

Least Concern on the IUCN Red List.[1] It inhabits forests and wooded wetlands.[2]
Of the four living species of fish owl, it is the most widely distributed, most common and best-studied. It occupies a range of over 7,000 km (4,300 mi).

Taxonomy

nominate subspecies
zeylonensis, which is smaller and darker than other subspecies
A brown fish owl in India

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.[3] 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.[4][5] The brown fish owl is now placed in the genus Ketupa that was introduced in 1830 by the French naturalist René Lesson.[6][7]

Four subspecies are recognised:[7]

Results of a

monophyletic group.[11]

Fossil records

In

Roman Sardinia, with no subspecies being recognized.[14]

The oldest remains date back at least to the

Strix" perpasta is unlikely to belong in that genus, and also sometimes merged with B. insularis.[13]

Description

A juvenile at Sim's Park, Coonoor, Tamil Nadu

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.[15]

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.[16][17] It is slightly larger than the buffy fish owl with a darker brown hue.[18][19]

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.[19][18]

Subspecies

  • Sri Lankan brown fish owl (K. zeylonensis zeylonensis) is the smallest and darkest coloured subspecies with a wing chord of 355 to 405 mm (14.0 to 15.9 in), a tarsus of 85 to 90 mm (3.3 to 3.5 in), a tail of 177 to 206 mm (7.0 to 8.1 in), and a bill of 42 to 48 mm (1.7 to 1.9 in). The wing length averages 92% shorter than in northern subspecies. One male was found to have weighed 1,100 g (2.4 lb).
  • Common brown fish owl (K. z. leschenaultii) occurs from the
    nominate subspecies
    . It has a wing chord of 370 to 430 mm (15 to 17 in), a tail of 186 to 210 mm (7.3 to 8.3 in), a tarsus of 71 to 90 mm (2.8 to 3.5 in) and a bill of 49 to 52 mm (1.9 to 2.0 in). The wing chord of 16 males in India averaged 402 mm (15.8 in) and their bills averaged 49 mm (1.9 in) while 15 females averaged 395 mm (15.6 in) in wing chord and 51.5 mm (2.03 in) in bill length. A male was found to weigh 1,105 g (2.436 lb) and a female was found to weigh 1,308 g (2.884 lb).
  • Western brown fish owl (K. z. semenowi) occurs from southern Turkey through Iran and Pakistan to
    northeastern India
    . It is paler and slightly larger than the common brown fish owl with a somewhat tawny hue. Its wing chord is 396 to 434 mm (15.6 to 17.1 in) with a tarsus of 74 to 90 mm (2.9 to 3.5 in), a tail of 197 to 214 mm (7.8 to 8.4 in) and a bill of 49 to 54 mm (1.9 to 2.1 in).
  • Eastern brown fish owl (K. z. orientalis) occurs in north-eastern Myanmar, Vietnam and southeastern China and
    Hainan Island
    . It is somewhat darker than the common brown fish owl with a larger tarsus. Its wing chord is 365 to 457 mm (14.4 to 18.0 in), with a tail of 195 to 210 mm (7.7 to 8.3 in) and a tarsus of 67 to 70 mm (2.6 to 2.8 in).

Distribution and habitat

An adult Brown Fish Owl at Barpeta Assam by Hedayeat Ullah

The brown fish owl is an all-year resident throughout most tropical and subtropical parts of the

arid regions. Regardless of habitat, it rarely strays far from larger bodies of water such as rivers and lakes.[16][20][19]
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.[15]

Behaviour and ecology

Foot showing adaptations to catch fish

The calls of the buffy fish owl are described as a deep humming boom-uh-boom, a hup hup hu and a loud huhuhuhuhuhuhu.[21][2] A trisyllabic tu-hoo-hoo is seemingly the territorial song emitted before breeding. Its call has been described as comparable to that of a distant Eurasian bittern (Botaurus stellaris).[22]

The buffy fish owl is

invertebrates than either of those species, the eagle feeding mainly on fish followed by water birds and the eagle owl feeding mainly on mammals followed by land birds. If hungry, brown fish owls will scavenge carrion, a rare behavior for owls. A case where a putrefying crocodile (Crocodylus ssp.) carcass was consumed by this species was observed.[19][18][16]

As mentioned above, the

climate change, but the giant pikas of Sardinia and Corsica still existed around 1750, finally succumbing to habitat destruction, introduced predatory mammals and overhunting soon thereafter.[12]

Reproduction

Egg of the brown fish owl

Brown fish owls breed from November to April, with activity tending to peak a bit earlier in the north of their breeding range and a bit later in the more tropical south of their breeding range. The breeding season is concurrent with the dry season, which has the benefit of low water levels and thus crabs and fish being more readily assessible. However, most other owls and diurnal raptors also primarily breed in the dry season as well. As owls do not build nest, brown fish owls are somewhat opportunistic when it comes to nesting sites. Brown fish owls frequently nest in shady spots such as old-growth mango trees (Mangifera ssp.), fig trees, including Ficus religiosa and Ficus benghalensis, Shorea robusta and other large trees in lowland forests. Outside of the bare surface of large branches, nests are often in spots such as overgrown eroded ravines and steep riverbanks with natural holes. However, it may also nest near suitable villages, along wet roadsides, jheels, canals and rice fields. Usually nest are large natural holes, in hollows or at the base of large branches. Deserted nest built by fish eagles and vultures are also sometimes used as nesting locations. Other nesting sites have included rock ledges, caves in shady cliff faces and stone ruins. The clutch is two or occasionally just one egg. 10 eggs in India averaged 58.4 mm × 48.9 mm (2.30 in × 1.93 in) in sizes, with eggs of fish owls to the north averaging slightly larger. Incubation is 38 days or somewhat less, and the young fledge after about seven weeks. The downy chicks are mostly an off-white color and develop into a paler version of adults by their second year.[19][18][16][15]

Threats

Apparently in India, during the festival of Diwali, thousands of owls are killed - though programs to counter this practice are underway - including this species due to superstitious beliefs about the evil nature of owls and as an attempt to gain the power of black magic.[15] Habitat destruction will eventually cause the species to desert a region. Due to this, it seems to be extinct as a breeding bird in Israel nowadays, attributable largely to damming practices leading to drying up of many waterways. In Israel, it was decimated by the use of the rodenticide thallium(I) sulfate, which in addition to potential direct exposure through rodents also poisons surface waters.[19]

References

  1. ^
    doi:10.2305/IUCN.UK.2016-3.RLTS.T22689012A90010491.en
    . Retrieved 3 February 2022.
  2. ^
    ISBN 9781408162651
    .
  3. ^ Gmelin, Johann Friedrich (1788). Systema naturae per regna tria naturae : secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis (in Latin). Vol. 1, Part 1 (13th ed.). Lipsiae [Leipzig]: Georg. Emanuel. Beer. p. 287.
  4. ^ Brown, Peter (1776). Nouvelles illustrations de zoologie : contenant cinquante planches enlumineés d'oiseaux curieux, et qui non etés jamais descrits, et quelques de quadrupedes, de reptiles et d'insectes, avec de courtes descriptions systematiques [New illustrations of zoology, containing fifty coloured plates of new, curious, and non-descript birds, with a few quadrupeds, reptiles and insects]. London: Imprimé pour B. White. p. 8, Plate 4.
  5. ^ Ferguson, Donald (1907). "Joan Gideon Loten F.R.S., the naturalist governor of Ceylon (1752-57), and the Ceylonese artist de Bevere". Journal of the Ceylon Branch of the Royal Asiatic Society. 19: 217–271.
  6. ISBN 978-0-9568611-1-5
    .
  7. ^
    Rasmussen, Pamela, eds. (August 2022). "Owls"
    . IOC World Bird List Version 12.2. International Ornithologists' Union. Retrieved 24 December 2022.
  8. ^ Sarudny, N. (1905). "Zwei ornithologische Neuheiten aus West-Persien". Ornithologisches Jahrbuch. 16: 141–142.
  9. ^ Temminck, C. J. (1838). "Hibou Leschenault. Strix Leschenault". Nouveau recueil de planches coloriées d'oiseaux : pour servir de suite et de complément aux planches enluminées de Buffon, édition in-folio et in-4⁰ de l'Imprimerie royale, 1770. Vol. II. Paris, Strasbourgh, Amsterdam: F. G. Levrault, Legras Imbert et Comp.
  10. ^ Delacour, J. F. (1926). "Ketupa celonensis orientalis". Bulletin of the British Ornithologists' Club. 47 (308): 11.
  11. PMID 23211719
    .
  12. ^ a b Mourer-Chauviré, C.; Weesie, P. D. M. (1986). "Bubo insularis n. sp., forme endemique insulaire de grand-duc (Aves, Strigiformes) du Pléistocène de Sardaigne et de Corse" (PDF). Revue de Paléobiologie. 5: 197–205. Archived from the original (PDF) on 2021-08-16. Retrieved 2009-06-23.
  13. ^
    CiteSeerX 10.1.1.694.5550
    .
  14. ^ Vigne, J.-D.; Bailon, S. & Cuisin, J. (1997). "Biostratigraphy of amphibians, reptiles, birds and mammals in Corsica and the role of man in the Holocene faunal turnover". Anthropologica. 25 (26): 587–604.
  15. ^
    ISBN 9781472905932
    .
  16. ^ a b c d Grimmett, R., Inskipp, C., & Inskipp, T. (1999). Birds of India, Pakistan, Nepal, Bangladesh, Bhutan, Sri Lanka, and the Maldives. Princeton: Princeton University Press.{{cite book}}: CS1 maint: multiple names: authors list (link)
  17. ISBN 9781909612839
    .
  18. ^
    ISBN 9781408108840
    .
  19. ^
    ISBN 978-0-262-22035-4
    .
  20. ^ Singh, A. P. (2002). "New and significant records from Dehra Dun valley, lower Garhwal Himalayas, India" (PDF). Forktail. 18: 151–153. Archived from the original (PDF) on 2008-07-25.
  21. S2CID 216342637
    .
  22. ^ Harrison, J. (2011). A field guide to the birds of Sri Lanka (Second ed.). Oxford: Oxford University Press.

Further reading

External links

Wikimedia Commons has media related to Ketupa zeylonensis.
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