Bird Research News

Vol.8 No.7

Ryukyu Scops Owl

2011.7.23.

Ryukyu-konohazuku (Jpn) Otus elegans

Morphology and classification
Classification: Strigiformes Strigidae
The populations of Okinawa and Minami-daito(-jima) Islands will be primarily discussed in this paper.

Population of Okinawa Island
Total length: about 20cm
Wing length:162.0-177.0 mm
Tail length: 69.0-82.0mm Culmen length: 18.8-24.0mm
Tarsus length: 29.2-33.5mm Weight:
94.0-125.0g
Polpulation of Minami-daito Island
Total length:
about 18cm
Wing length:♂148.5-165.5mm
Tail length:♂64.43-80.20mm
Culmen length:♂18.31-22.90mm
Tarsus length:♂28.13-31.74mm
Weight:♂70.0-102.0g

noshima Island, Fukuoka Prefecture, northern Kyushu in 2008.
Currently, subspecies O.e.interpositus lives only in Minami-daito
Island of the Daito Islands.

Habitat:
Ryukyu Scops Owls are originally a mature forest dweller, but
nowadays they also live in a relatively open habitat, such as arable
land (Photo 2). They generally breed in a tree cavity in the wood,
but some of them nest in man-made structures. They use as a feeding ground a considerably open habitat, such as cropland, meadows and residential quarters, if perching places are available. Inshort, they are well adapted to artificially modified environments.

♀149.0-165.0mm♀61.51-77.01mm♀19.47-22.51mm♀28.05-31.77mm♀78.0-111.5g

The measurements of Okinawa Island population are based on 17 males (Toyamapers. comm.). Measurements of Minami-daito Island population are based on 86
males and 54 females of one year and over from 2002 to 2009. Tail lengths exclude
those of birds with worn out rectrices. Weights exclude those of females immdiately
before egg-laying. The population of Minami-daito Island is remarkably smaller thanthose of the other regions (Severinghous et al. 2002).

Photo 2. (left) Habitat of Okinawa Island (Forest of the Yambaru region).
(right) Habitat of Minami-daito Island (Open cane fields with shelterbelts)

Appearance:
Males and females are similar in plumage coloration. They arebrown on the upperpart with an intricate pattern of black and yellowish brown flecks. The shoulder is vertically lined with whitespeckles. They are ashy brown on the underpart with brownish
black vertical stripes and fine lateral bars. The facial disc is grayand fringed with reddish brown feathers. The bill is deep gray. Theiris is yellow. They raise the reddish brown ear tufts when alerted.
The toes are bare and gray.

Vocalization:
The well-known hoot of Ryukyu Scops Owls is a male territory
call and males call "Kok, kohok" or "Kohok, kohok" repeatedly.
They also utter various calls depending on individuals and situations. For instance, females call "Gyohok" in a thick voice or"Fnee, fniyaa" like a cat in response to males. Males rarely calllike a cat as well. Both male and female hoot a single "Hoh--u"when they become tense. They threaten other birds or predatorswith "Shaa, shaa". They give out a sharp alarm call like "Kuok,
kuok, kuok" when the nest is
attacked. Females whisper "Purpur-pur" sweetly towards themale partner. Males shrill"Kyurrr" when copulating. This
voice may also be uttered by females when they receive foodfrom males during the courtshipperiod, and excited nestlings
when they are provided with food Photo 1. A Ryukyu Scops Owl
or when they fly to a branch.
parent delivering a huntsman
Nestlings beg for food in the nest,
spider to the nestling inMinami-daito Island.
calling "Gyooi, gyooi" or "Jaj-ja"[Masaoki Takagi]
continuously.

Distribution and Habitat
Distribution:
Ryukyu Scops Owls are classified into the following four subspecies: Otus elegans elegans of the Nansei Islands, O. e. interpositusof the Daito islands, O. e. botelensis of Orchid Island off southeastern Taiwan and O. e. calayensis of the Batan Islands and theBabuyan Islands, the northernmost Philippines. Ryukyu Scops Owls were also confirmed to occur in Oki-4Life history
1345 6 7breeding

89 10 11 12
wintering period

Breeding system:
Ryukyu Scops Owls are monogamous and breed once a year. They
do not attempt to breed again if they have failed in the first breeding. Both males and females sexually mature at the age of one, butfew birds can breed at this age in the habitat where unoccupied
breeding territories are in short supply. When males acquire aterritory, they try to attract females to form a pair. Pairs stay in theterritory almost throughout the year. Although they maintain theirpair-bond over the years, it is not uncommon for them to divorce.
In Minami-daito Island, for instance, extra-pair fertilization is
confirmed in about 15% of the nests.

Nest:
Ryukyu Scops Owls breed in a tree cavity. In the Yambaru regionof Okinawa Island, they generally use the old nest holes which
Okinawa Woodpeckers excavated in oaks (Castanopsis sieboldii
and Quercus stenophylla). The average nest size is 6.5cm at theentrance, 15 by 15cm at the base and 30cm in depth (Toyama2010). In farmland, on the other hand, they nest in the cavity ofCasuarina often used as a shelterbelt. More than 90% of the nest
trees are also Casuarina in Minami-daito Island where farmland
predominates. The nesting Casuarina was 57cm in diameter at
breast height on average, with a range of 27-88cm. The mean cavity size was 11.6cm by 39.8cm (with a range of 6-24cm by 10125cm) at the entrance and 52.4cm (with a range of 14-162cm) indepth (n = 30). A small number of Ryukyu Scops Owls also use
the cylindrical pit of Livistona chinensis snag with a broken upper
part

Clutch and egg sizes and egg color
The clutch size is 1-4 eggs. Both in Okinawa and Minami-daito
Islands, more than 50% is three eggs and about 30% two eggs. The
clutch of one or four eggs is rare. Eggs are laid at 1-2 day intervals. The egg is white with no flecks and 33mm by 27mm in size
(measured in Minami-daito Island).

Incubation and nestling periods and fledging rate
Ryukyu Scops Owls start to lay eggs in late April in Okinawa♪ http://www.bird-research.jp/1_shiryo/koe/ryuukyuukonohazuku_060312_okinawa_kaji.mp3
Kyoko Kajimoto2

Bird Research News

Vol.8 No.7

2011.7.23.

© Japan Bird Research Association
Sumiyoshi 1-29-9, Fuchu, Tokyo, Japan

バードリサーチ生態図鑑

Island (Toyama 2010) and in late March in Minami-daito Island.
Females alone incubate eggs. The incubation and nestling periods
are about 26 and 30 days, respectively. Females incubate nestlings
for about 10 days after hatching, while males exclusively feedthem. After that, males and females feed nestlings. Young areprovided with food by the parent birds in the natal territory for 2040 days after fledging. The fledging rate is 74% in Okinawa Island(n = 141) (Toyama 2010) and 79% in Minami-daito Island (n =100). The predation of snakes is primarily responsible for thebreeding failure in Okinawa Island, whereas the breeding failure isattributed to the predation of introduced black rats, weasels andferal cats in Minami-daito Island.

Roost:In Minami-daito Island, Ryukyu Scops
Owls usually roost in the woods of Livistona during the daytime. When perchedat the stem base of Livistona, it is noteasy to find them because they blend inwith brown fibers peculiar to palms. Inaddition, when an enemy approaches,
they make themselves slender and raise
their ear-tufts to mimic the stem of apalm tree, which doubles the camouflage
effect (Photo. 3).

Photo 3. A Ryukyu
Scops Owl mimicking the stem of apalm tree in Minamidaito Island. [AsukaHorie]

Diet and foraging behavior
Ryukyu Scops Owls are insectivorous. In Okinawa Islands, thediet of nestlings consists primarily of orthoptera (80%), such asProsopogryllacris and Gampsocleis, followed by stick insects andhouse lizards (Toyama 2010). In Minami-daito Island, on the otherhand, huntsman spiders and Periplaneta americana each comprise
25% of their diet, followed by orthoptera, house lizards and lepidoptera. They usually swoop down on their prey on the ground oron a tree from their perches. They occasionally fly-catch flying
insects as well. In Minami-daito Island, they prefer the dense
woods of Ficus retusa as a foraging site. They also capture theirprey in the fields of crop and meadows from the edge of a wood.

Topics of ecology, behavior and conservation● Difference in vocalization between subspecies
The vocalization of Ryukyu Scops Owls varies between regions. I
recorded the calls of 718 males in Orchid Island of Taiwan and 22
islands of the Nansei Islands (the southernmost island group ofJapan) to analyze them using a sound spectrogram. The analysis
showed that the calls were divided into two distinct groups by theKerama Strait between Okinawa and Miyako Islands. In addition,
the population of Minami-daito Island formed another vocalizationgroup independently of these two groups. It is assumed, therefore,that Ryukyu Scops Owls are classified into the following threegroups in terms of vocalization: birds north of Okinawa Island,
those west of Miyakojima Island and those of Minami-daito Island.

● Dispersal of young birds in a territory saturated habitat
It is extremely difficult for young Ryukyu Scops Owls to secure
their territory in Minami-daito Island because the suitable habitat
is limited to shelterbelts remaining in a narrow band and there isno space left to establish a new territory. The telemetry study of 38
fledglings showed that 16 birds survived until the next spring,
seven of which could not find anywhere to settle in and became
floaters. The males which fledged earlier acquired a territory clos-er to their natal site, but later fledglings dispersed further to establish their territory. Once male fledglings left their parents' territory,
they promptly settled in a vacant territory whenever they foundone. It is their strategy to acquire a territory on a first-come, firstserved basis.

● Should all introduced species be exterminated?
The environment of Minamidaito Island has been modified sogreatly and so many species havebeen introduced that little of theoriginal environment remains inthe island. As a result, four endemic subspecies of birds became extinct, but Ryukyu Scops
Owls have survived. It is Casuarina introduced to the island that
Photo 4. A female perched at theplayed a key role in conserving
entrance of the nest hole (thethe population of Ryukyu Scops
cavity of Casuarina) in MinaOwls. Since Casuarina grows
mi-daito Island. [Yuzo Nakquickly, it was planted for hardagawa]ening the soil of a marsh and as ashelterbelt after deforestation. In addition, Casuarina tends to forma cavity in it. Research showed that introduced Casuarina had 15times as many cavities as native Livistona, which Ryukyu Scops
Owls principally used as a nest tree before deforestation. As mentioned above, therefore, they mostly nest in the cavities of Casuarina now (Photo. 4). In Minami-daito Island where woodlands
have markedly declined, this introduced tree has provided Ryukyu
Scops Owls with their nest sites. In some areas of Japan, efforts
have been made to restore modified environments to the originalstate, but as in Ryukyu Scops Owls, some native species havealready adapted and depended on modified environments. Therefore, the restoration of environments or the control of introduced
species should be performed with due consideration.

Literature
Akatani K., Matsuo T. & Takagi M. 2011. Breeding ecology and habitat use of theDaito Scops Owl (Otus elegans interpositus) on an oceanic island. J. Raptor Res.
45(4):315–323.
Severinghaus L. L., Hsu Y., Chen C. & Tsai C. 2002. Population differentiation ofelegant scops owls (Otus elegans) on Ryukyu Islands (Abstract). International
symposium: Molecular Perspectives on the Process of Dispersals, Isolations andDiversifications of Animals and Plants in the East Asian Islands: 15-16.
Takagi M., Akatani K., Matsui S. & Saito A. 2007. Status of the Daito Scops Owl
on Minami-daito Island, Japan. J. Raptor Res. 41(1):52-56.
Toyama M. 2010. Niche differences in syntopic populations of two similar sized
scops owl species (Otus elegans and Otus semitorques): factors facilitating theircoexistence. Doctoral thesis, Hokkaido University, 2010.

AuthorKana AKATANII enrolled in the lab of Departmentof Biology and Geosciences, Osaka
City University in 2000. I carried out
a study on Ryukyu Scops Owls in
Minami-daito Island for eight years
from 2002. I really learned a lot
from the people and wildlife of theisland. I am now learning graphic
design and illustration to convey thecharm of wildlife to wide range ofpeople.
kana.akatani@gmail.com

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