Bird Research News

Vol.9 No.1

Ryukyu Robin

Akahige (Jpn) Luscinia komadoriMorphology and classification
Classification: Passeriformes Muscicapidae
Natural wing length: ♂ 75.5 ± 1.6mm
Tail length:♂ 48.0 ± 2.3mm
Tarsus length:♂ 28.3 ± 0.7mm
Nalospi length:♂ 9.6 ± 0.5mm
Head length:♂ 37.9 ± 0.9mm
Weight:♂ 23.0 ± 1.3g

♀ 72.5 ± 1.6mm♀ 45.6 ± 1.9 mm♀ 27.9 ± 0.7mm♀ 9.6 ± 0.5mm♀ 37.5±0.8mm♀ 24.4 ± 2.4g

Measurements in Nakanoshima Island of the Tokara Islands including those of birds
recaptured in different years (♂ = 433, ♀ =364).

Appearance:
The plumage coloration varies between subspecies. The males of thenominotypical subspecies L. k. komadori are orange on the upperpart
and white on the underpart. They areblack from the forehead to the throat
and on the flank (Photo 1). The
plumage of females is tinged withbrown all over with no black parts.
In subspecies L. k. namiyei, on the Photo 1. Male of Ryukyu
Robins L. k. komadori
other hand, both males and females
are brown-tinged orange on the upperpart and grayish white on theunderpart. The males lack a black patch on the flank. .

Vocalization:
Both males and females sing. They warble like "Hee, hyor-hyorhyor", "Tseen, hiyo-hiyo-hiyo", and "Tsee, pirrrrr". The Ryukyu
Robin song characteristically has a long prelude followed by arhythmical repetition. In addition to individual variations, theyoften add subtle variations to their song every time they sing. Thesong differs between subspecies as well. For instance, the repetition part of the song in L. k. komadori is shorter which gives a
restless and monotonous impression. Ryukyu Robins utter an
alarm call of "tseee", when other animals approach their nest. They
normally call like "gyr" in a thick voice.

Distribution and Habitat
Distribution:
Ryukyu Robins L. k. komadori breed in the Danjo Islands and thenorthern part of the Ryukyu Archipelago, such as the Tokara andthe Amami Islands. The breeding populations north of the Tokara
Islands are basically summer residents which winter in the thesouthernmost part of the Ryukyus (known as the Sakishima Islands). However, some breeders of the Amami Islands are also
migrants. L. k. namiyei, on the other hand, occurs in the Central
Ryukyus (northern part of Okinawa Island) as a year-round resident. In the non-breeding period, Ryukyu Robin unknown subspecies have been recorded in Kyushu (the southernmost main islandof Japan), the Korean Peninsula and Taiwan as well.

Habitat:
Ryukyu Robins prefer a laurel forest with well-developed undergrowth, but they also occur in a thicket of Ryukyu bamboos Pleioblastus linearis in the Tokara Islands. Their songs are heard fromcoastal laurel forests to shrub woods at an altitude of almost 800m
in the breeding period. They generally inhabit mature laurel forests, but are also commonly found in secondary forests, temple andshrine woods, and groves around a residence.

Life history
41 2 3 4 5 6 7 8 9 10 11 12
non-breeding
breeding season migrationseason♪ http://www.bird-research.jp/1_shiryo/koe/akahige_090721_tokara_seki.mp3
Shin-ichi Seki2012.1.27.

Breeding system:
Ryukyu Robins are basically monogamous, but there was a malewhich fed the nestlings at two different nests concurrently. They
establish a territory with an area of about 0.2-0.3ha, and bothmales and females defend their territory. In the Tokara Islands,
they may breed consecutively up to three times (four times in Okinawa Island) in a breeding season. They usually maintain their pair-bond during the breeding period. When both the male and femaleof a pair survive the winter, they mostly retain their pair-bond as
well (15/19 pairs). Only females build a nest and incubate eggs,
but both males and females feed the nestlings and fledglings.
When they attempt the second or third breeding, females start tobuild a nest immediately after the nestlings have fledged, andmales mostly take care of the fledglings after females begin toincubate.

Nest:
Ryukyu Robins build a cup-shaped nest
using dead pine needles, dead vines, thedead leaves of broad-leaved trees and bamboos, and fan palm barks. They line theinner cup with fine vines and dead leaves
with only veins left. The nest is built in awide variety of sites, such as a base ofbamboo branches, the upper side of a palm Photo 2. Eggs in a nest
built in a thicket ofleaf, branch tips of a broad-leaved tree,
Ryukyu bambootree cavities, cracks of a tree trunk, snags
of a tree fern and ledges of rock. They are also ready to use artificial structures including nest boxes.

Egg:
The mean clutch size is 3.3 ± 0.6 egg with a range of 1-5 eggs (n =202). The egg weight is 3.3 ± 0.3g on average (n = 428). The egg
is white or pale brown with dark brown speckles scattered densely
on the blunt end but sparsely on the other areas.

Incubation and nestling periods and fledging rate:
The mean incubation period is 12.8 ±0.8 days (range 11-15 days) assumingthat they start incubating when laying
the last egg (n = 118). The hatchingrate is 90.2% on average in a nest freefrom predation (n = 529 eggs). The
mean brood size is 3.0 ± 0.8 birds (n =158). The mean nestling period is 14.2
Photo 3. Nestlings in a nest.
± 1.3 days (range 12-17 days; n = 63).
In the Tokara Islands, netstlings fledged successfully in 29% of theartificial nest boxes, while eggs or nestlings were lost due to thesupposed predation of weasels in 65% and eggs were abandoned
as a result of nest damage in 6%. There was no great difference infledging rate between a nest box and a natural nest. Predation wasmostly responsible for nestling mortality and nest damage.

Migration:
Ryukyu Robins breeding in the Tokara Islands are basically asummer resident. They arrive in the islands from late March toearly April and most of them leave the breeding grounds from
September to October for the Sakishima Islands to winter. The
return rate of adult birds to the breeding grounds varies between
the years. The annual survival rate considering recapture probability was estimated to be 61% in males (n = 96) and 47% in females(n =67). The return rate of fledglings to their natal site was 6.8%
(n = 192). The population of Okinawa Island and most of the populations of Amami-Oshima and Tokunoshima Islands are yearround residents.
* Life history data were primarily collected in Nakanoshima of the Tokara Islands.
Some residents of the Amami Islands and Okinawa Island start breeding as early as at
the end of February.

Bird Research News

Vol.9 No.1

2012.1.27.

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

バードリサーチ生態図鑑

Diet and foraging behavior
The diet of Ryukyu Robin nestlings consists of imagos and larvaeof insects (lepidoptera, diptera, hemiptera, orthoptera, blattodea,
thysanura, etc.) and other invertebrates occurring on the groundand the soil surface, such as spiders, centipedes and earthworms.
Although parent birds are frequently observed to peck at or dig forfood on the ground, the nestling diet suggests that they also forage
on trees with high frequency. They are also assumed to feed off thefruits from trees because fruit juice sometimes adheres to the corners of the bill when adult birds are captured for scientific purposes.

Topics of ecology, behavior and conservation● Phylogenetic origin of the Ryukyu Robin
Since Ryukyu Robins and Japanese Robins Luscinia akahige havemuch in common in character and ecology, they are assumed to besister species. Since Japanese Robins are remarkably similar inplumage coloration to European Robins Erithacus rubecula, thesethree species have been traditionally classified into genus Erithacus. Not a few authors have advocated the theory, however, thatRyukyu and Japanese Robins are closer to genus Luscinia because
there are not only a break in distribution but also many differencesin character and ecology between European Robins and the two
East Asian species. The recent analyL. k. komadori
sis of DNA has showed that Ryukyu
L. k. namiyei
Luscinia akahige
Robins are closer to genus Luscinia
Luscinia sibilansof East Asia, such as Rufous-tailed
Luscinia cyane
Robins Luscinia sibilans and SiberianTarsiger cyanurus
Luscinia calliope
Blue Robins Luscinia cyane, andPhoenicurus auroreus
diverged from from European Robins
Erithacus rubeculain ancient times. It has been revealed,
Luscinia svecicaon the other hand, that genus Lusinia
0.01 genetic distanceis not a single group either. An inde- Fig. 1. Maximum likelihood
pendent generic name may be adoptdendrogram estimateded to the species-group of East Asia
from the base sequence
including Ryukyu Robins in the fuof cytochrome-b area of
mitochondrial DNA.
ture.

● Variations in life history and group divergence between
the island groups

endurance
maneuverability

Ryukyu Robins vary in morphology and ecology from one islandgroup to another. The morphology differs between the subspecies
as well. L. k. komadori varies greatly in breeding and migration
behavior depending on the island group. Do these variations correspond to genetic backgrounds ? Based on the mtDNA sequencedata, each of the two subspecies formed genetically distinctive
clade, which diverged more than several hundred thousand years
ago. In addition, three distinctive subgroups of populations were identified
within L. k. komadori by population
genetic analysis: sedentary Tokunoshima and Ohshima groups and migratory High Low
Tokara group. When the wingtip shape,that is a highly heritable trait and wellassociated with migratory habit, wascompared, L. k. komadori had significantly more pointed wing than that ofLow Highthe southern sedentary L. k. namiyei.
The difference was not so apparent be- Photo. 4. Difference inwing shape between L.
tween the sedentary and migratory
k. komadori of thegroups within L. k. komadori, suggestTokara Islands (above)
ing that this northern subspecies hasand L. k. namiyeidifferentiated as primarily a migratory(below).

lineage from southern sedentary lineage L. k. namiyei. Then, sedentary populations (of Tokunoshima and Amami-Ohshima Islands)
arose recently in the migratory subspecies (L. k. komadori), which
triggered another differentiation in the subspecies.

● Migration of Ryukyu Robins
Ryukyu Robins winter in a considerable number in the SakishimaIslands. They use a wide variety of woodlands as a wintering site,ranging from the primeval forests of Iriomotejima Island to theshrine groves of small islands consisting primarily of farmland,such as Kuroshima Island. A limited number of Ryukyu Robins
have formally been observed in the Sakishima Islands probably
because they rarely sing or come out into an open habitat in thewintering grounds. The analysis of mitochondrial DNA genotypesof birds captured in the Sakishima Islands showed that 87% of thewintering birds came from the Tokara Islands, 8% Amami-OshimaIsland and 5% Tokunoshima Island (n = 37). Although the populations of Tokunoshima and Amami-Oshima Islands were assumed
to be sedentary until then, it was revealed that they included birdswhich migrated to the Sakishima Islands. It is still unknown whattypes of birds migrate or stay in the breeding grounds. Incidentally, there is no record of Ryukyu Robins from the Sakishima Islands in the breeding period. It is highly unlikely, therefore, thatthe breeding population of the Sakishima Islands that has been
once described as L. k. subrufus actually occurs in those islands.

Literature
Kawaji N. & Higuchi H. 1989. Distribution and status of the Ryukyu Robin Erithacus komadori. J. Yamashina Inst. Ornithol. 21:224-233.
Sangster G., Alstrom P., Forsmark E. & Olsson U. 2010. Multi-locus phylogenetic
analysis of Old World chats and flycatchers reveals extensive paraphyly atfamily, subfamily and genus level (Aves: Muscicapidae). Mol. Phylogenet. Evol.
57: 380-92.
Seki S-I. 2006. The origin of the East Asian Erithacus robin, Erithacus komadori,inferred from cytochrome b sequence data. Mol. Phylogenet. Evol. 39: 899-905.
Seki S-I. 2002. Estimating the survival rate and dispersal distance of the Ryukyu
robin, Erithacus komadori. Kyushu J. For. Res. 55:171-172. [J]Seki S-I. 2009. Population trends and molecular phylogenetic position of the isolated Ryukyu Robin Erithacus komadori on the Danjo Islands, Japan. Jap. J. Ornithol. 58:18-27. [J+E]
Seki S-I. 2010. Recent status of the Ryukyu robin Erithacus komadori in the outlying habitats (II): Yaku-shima and Tanega-shima in the Ohsumi Islands. Kyushu
J. For. Res. 63: 95-96. [J]Seki S-I. & Ogura T. 2007. Breeding origins of migrating Ryukyu Robins Erithacus komadori inferred from mitochondrial control region sequences. Ornithol.
Sci. 6:21-27.
Seki S-I., Sakanashi M., Kawaji N. & Kotaka N. 2007. Phylogeography of theRyukyu Robin (Erithacus komadori) population subdivision in land-bridge
islands in relation to the shift in migratory habit. Mol. Ecol. 16: 101-113.
Seki S-I., Tokorozaki S., Mizoguchi F., Takagi S., Nakamura N. & Crystal F. 2011.
Avifauna of the Tokara Islands, northern Ryukyu Archipelago. Bulletin of FFPRI
10:183-229 [J+E]
Languages of literature cited other than English: [J] in Japanese, [J+E] in Japanesewith English summary.

AuthorShin-ichi SEKI Forestry and Forest Products Research Institute
The Tokara Islands, my major research field, is a wonderful place forornithologists, full of island endemics. It is almost 18 years since I firststarted studying the ecology of the Ryukyu Robin there. Nevertheless,it was a difficult work to write this small article. The research on thissuperb singer is still on its way, and I
usually experience something new
every year. I am looking forward torewrite this guide in the near feature
based on such new findings.
seki@ffpri.affrc.go.jp

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