Ketupa ketupu (Horsefield, 1821)
(Adapted from photo by: Annie Irving Permission granted)

Taxonomy & Systematics

Original description

The original description of this species has been recognised to be by Thomas Horsfield in 1821, in the publication Transactions of the Linnean Society of London under the section XIV Systematic Arrangement and Description of Birds from the Island of Java. [2]

Type Specimen

Type specimen is located in British Museum (Natural History) [3]

Changes in Genus

Though originally identified to be part of the Strix genus by Horsfield, this species was later relegated to the Ketupa genus instead by Lesson (1830), together with 3 other Fish Owl species found in Asia, K. blakistoni, K. flavipes and K. zeylonensis, consisting 4 species in total, based on their distribution and their specialised adaptations to hunting of fish and other aquatic organisms.

However, there have been attempts to revise the status of Ketupa as a genus using phylogenetics, suggesting that they should be under the genus Bubo instead. A phylogenetic study of Owl species using the DNA-sequences of mitochondrial cytochrome-b gene has been done by Wink & Heidrich (1999)[4] , this showed the close relation of the Ketupa genus to three other Bubo species B. lacteus, B. nipalensis and B. sumatrana, with a distance of 10.2% between zeylonensis and nipalensis and 9.2% between zeylonensis and sumatrana[5] . A further study using nuclear marker LDHb intron DNA, further corroborated with the findings of the first study (Wink, Sauer-Gürth & Fuchs, 2004)[6] . The following phylogenetic tree is the latest findings found in König et. al (2008)[7] , based on the combined dataset of mitochondrial cytochrome-b (Will & Heidrich, 1999)[4] and the RAG-1 sequences, to show that ketupu, together with zeylonensis are nested in the Bubo genus.

Subspecies

Four subspecies of Ketupa ketupu have been listed in König et al (1999)[8], mainly differentiating in their localities

However, there are different opinions about subspecies i.e. ITIS (Integrated Taxonomic Information Systems) only lists K. k. ketupu and K. k. minor as the 'direct children' of Ketupa ketupu.

Description

For the general anatomy of owls, click here
Descriptions are summarised from (König et. al, 1999)[8] with additional information from owlpages.com [9]

Measurements

Length: 40-48cm.
Wing length: 295-390mm.
Tail length: 160-181mm.
Weight: 1028-2100g.

Anatomy

Adult and juvenile

Diagnosis

Similar Species

Fish-owls, or fishing owls, are generally considered to be in two genera Ketupu and Scotopelia. The genus Ketupa only consist of 4 species distributed over most of Asia, in contrast to the Scotopelia consisting of 3 species found in Africa. [10] Scotopelia (African Fish Owls) are also large and powerful. However, Scotopelia lack ear tufts, loose feathering on their heads which gives them a characteristic shaggy, maned look. [10]

The Fish Owls of Ketupa bears close physical similarity to the genus Bubo (Eagle Owls) in terms of having similar prominent ear tufts, colour, size and and heavy build. However, they differ from Bubo in three main aspects in relation to their specialization of their diet on fish (Adaptations for hunting)

(1) Feet; devoid of feathers

(2) Face: less prominent facial disc

(3) Loss of soft fringes in rear edges of wings

Ketupa sp. are generally distinct in their geographical distribution, however there are certain sympatric areas in which the geographical range overlaps. Ketupa ketupu is sympatric with only two of the Ketupa species, K. zeylonensis and K. falvipes.

Voice

A repertoire of long drawn out shrill and wheezy notes. Hissing sounds and a rattling kutook, kutook, kutook, kutook, kutook, kutook... other vocalisations include a ringing pof-pof-pof-… and high hie-ee-ee-eek-keek notes, a musical to-whee to-whee. Also a soft monotonous and rapid pup-pup-pup-pup-pup..., utterered by a displaying pair. [8][9][11]The female has a slightly higher voice than the male.[8]The voice of the Buffy Fish Owl is probably the most recognizable of the four Ketupa species, being higher pitched and more musical than the other three species. [10]

Other recordings available at xeno-canto.org

Biology

Habitat

Usually waterside trees with dense foliage. [10]
Prefers middle storey or tall trees along sluggish streams and meandering rivers through the forest or woodland, of which mango trees have been observed to be popular in the tropical areas. [10] Have been observed to be perching on the roofs of houses in rural settlements as well. [11]
Also found at a wider range of habitats near water, including mangrove swamps, beach forests, freshwater swamps or even clusters of trees nearby human-created water bodies like rice fields, fish-ponds and reservoirs and sometimes wooded sub-urban gardens [10][11]

Active Hours

Owls are nocturnal predators, active during the night and roosting in the day, in contrast to the diurnal birds of prey. Fish Owls emerge from their roosts in late afternoon on occasion, and thus they are sometimes regarded as semi-diurnal. However, they rarely hunt during those occasions, rather, they would only hunt after dusk, as with all other species that are considered thoroughly nocturnal.[10] Frequently seen flying low at dusk. [11]

Roosting

Strongly territorial, tends to be evenly spaced out in the habitat.
Perches singly most of the time. Can be found in a pair on the same tree, but pairs are mostly observed to be roosting in separate trees within proximate radius of each other. [10]
Usually perches with one foot on the branch and the other hidden among the body feathers. Its eyes are not necessarily closed throughout the day, it can also be half-opened or opened during roosting. Easily disturbed, often already wide awake before observer locates it. In the presence of noisy trekkers, it would become tense, with eyes wide-open and ears erect together with all the feathers around. [8][12]

Feeding

Diet
Feeds mainly on fish, frogs, crustaceans, reptiles (lizards) and insects.
Also: Small mammals (rats, mice); Small birds; Large insects (beetles)
Occasionally: Bats, carrion or carcass (reported feeding on a dead crocodile and remains of a badger Mydaus javanensis in Java) [8][11]

Hunting
They often descend to the ground, and perch at the water’s edge or from a tree on a wooded bank. They would watch and wait for their prey to swim within striking distance, then swoop in and snatch their prey from the water’s surface with their claws, unlike the bodily plunging into the water body as in the manner of an osprey. They might also wade in shallow streams, often incidentally during bathing, occasionally they would snatch crabs, frogs, fish, aquatic insects from the water. [8][9][10]

Adaptations for hunting
Their feet are specialised to increase effectiveness of aquatic prey capture in three ways. [10]
(1) Lack of feathers on tarsi: Feathered legs would have been drenched and waterlogged with frequent plunging into the water for prey capture, thus the lack of feathers would optimize the capture of prey in Fish Owls.
(2) Underside of toes covered in numerous sharp edged and spiky scales: Enables them to have a good grip on the slippery and wet fish and other aquatic prey.
(3) Claws are long and curved with a sharp, lower cutting edge: Similarly gives the Fish Owl a stronger grip on its prey after capture.
owl species, that enables silent flight in owls during hunting. Presumably, this could be due to their prey being not so able to pick up airborne sounds, hence little need to conceal its presence as it swoops in to capture its prey.

[10]

[10]Pellets

Though pellets have been commonly observed for most nocturnal and diurnal birds of prey, this species Ketupa ketupu, does not seem to produce firm pellets or pellets of any real consistency. Instead, the undigested material such as bones, frog and insect remains are ejected in pieces and falls to the ground below the roost. Food remains never found beneath a nesting site, only in the nest. [8]

Life History

Breeding

Mainly during February to April, varies between different localities.
West Java: less commonly in May to July
Malay Peninsula: less commonly in April and September to January.[8]

Both sexes are particularly noisy before breeding, and pairs participate in duet which may continue for many minutes. [9] Vocalisations usually start one month before the nesting period.[13] The male uses calls and songs to attract the female or the renew the pair-bond with its mate. Courtship feeding possibly occurs too. [13]
Females are always larger than males. (For more hypotheses on why, click here)

Nest

Does not build its own nest, instead scratches out a small depression in the centre of a bird’s-nest fern, or a humid-rich debris of decayed leaves. No special structure or lining.
Frequently nests on top of bird’s-nest ferns (Asplenium nidus).
Also, in a thick bough covered by ferns, moss and orchids or tree hollows
Sometimes in old nests of raptors (e.g. Brahminy Kite Haliaster indus)
May resort to caves in rocky sites i.e. waterfalls, but rarely. [8][9]

Brood

Usually one, but sometimes two eggs are laid.
Eggs: Broadly oval, dull white or with moderate gloss.
Egg size: 48mm x 52mm,
Incubation period: About 28-29days
In the case when two eggs are laid, generally only one chick survives
Chick will fledge after 6 weeks. [8][9]

Juvenile

When faced with a threat like when approached by people or when annoyed, the juvenile has been observed to make a cup-cup-cup sound by clapping its beak. The sound might be caused by the clicking of the tongue rather than the the bill. This sound would then cause the parent to fly down close to observe what is going on.[14]
Seems to be able to recognise people who do not pose a threat, as observed that the juvenile stopped its beak clapping after the observer stood there without doing anything for four hours. [14]

Has been observed to frequently yawn for long durations, holding its mouth open for 10-15 seconds at times. Presumably not just yawning but to strengthen its ‘jaws’, just as birds usually flap its wings to strengthen them as well as its body. [15]

Mortality

They have been known to live for over 30 years in captivity[9]

Movement

Resident (not migratory). Exceptionally, vagrants recorded (One specimen Cocos Keeling Is., Indian Ocean, 1050km outside main range).[8]

Distribution

Global

List of countries and areas with record of Ketupa ketupu [8][9][16]

Singapore

[17][18]

[19]

[20]

Status and Conservation

IUCN: Least Concern [16]
"This species has an extremely large range, and hence does not approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence <20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). The population trend appears to be stable, and hence the species does not approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size has not been quantified, but it is not believed to approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern."
-From IUCN

CITES: Appendix II [21]
"STRIGIFORMES spp. (Except Sceloglaux albifacies and the species included in Appendix I)"

"Appendix II shall include:
(a) all species which although not necessarily now threatened with extinction may become so unless trade in specimens of such species is subject to strict regulation in order to avoid utilization incompatible with their survival; and
(b) other species which must be subject to regulation in order that trade in specimens of certain species referred to in sub-paragraph (a) of this paragraph may be brought under effective control."
-From CITES

Anthropogenic threats

Poaching
There have been several instances of Ketupa ketupu being discovered among the animals that have poached from the wild illegally and sold in the bird trade as pets. It seems that this phenomena is especially prominent in Indonesia, as the keeping birds as pets is widely popular in Indonesia and though illegal, there still persists several bird markets in many of the large cities in Indonesia like Medan in North Sumatra. [22][23]

Persecution
They might be killed due to their predation on fish and aquatic organisms, if they are seen as threats to human livelihood depending on fish stocks, especially if these Ketupa ketupu inhabit and hunt in areas near human constructs such as fish ponds.

Poisoning
In highly urbanised areas, there is commonly poisoning of rats to prevent their proliferations. However, this poses a threat to the owls as they include small mammals such as rats in the diets of these owls, and there is a risk of them being poisoned on consumption of these poisoned rats.

Loss of Habitat
Though they seem to be fairly adaptable, occupying a wide range of wooded and watery habitats[24] , in highly urbanised societies like Singapore, where there is increasingly limited areas of wooded habitats for them to inhabit, they might gradually become pushed to extinction.

External Resources
The Owl Pages: For all kinds of information about owls
Oriental Bird Images: For more photographs of Ketupa ketupu and other birds
The Internet Bird Collection : For more videos, photos and media on the Ketupa ketupu or other birds
xenocanto: For more recordings of bird calls
Bird Ecology Study Group: For more local information about birds in Singapore

References

This page was authored by Song Xinru

Last curated in 2014