Bird Research News

Vol.4 No.2

2007.2.14. Last Revised: 2014.2.3.

Japanese Bush Warbler
Morphology and classification
Classification: Passeriformes Cettidae
Total length:
Wing length:
Tail length:
Culmen length:
Tarsus length:
Weight:Approximately 14-15.5cm♂ 62.2-67.7mm♀ 51.3-57.0mm♂ 64.8-73.1mm♀ 53.4-60.7mm♂ 10.6-13.8mm♀ 9.9-11.7mm♂ 24.5-27.1mm♀ 21.4-23.2mm♂ 14.8-22.3g♀ 10.0-13.7g

Total length after Yoshii (1988), and the other measurements are by the author inNiigata Prefecture in the breeding season (Hamao 1992).

Appearance:
Both male and female areolive brown on the upper
part and beige on the underpart. They have creamy
superciliaries. The plumage
coloration varies slightly
between the subspecies or
the local populations.

Distribution:
Japanese Bush Warblers are distributed in northeastern China, theRussian Far East, the Korean Peninsula and Japan.

Habitat:Japanese Bush Warblers especially prefer bushes at a forest edge
and in an open area of a forest from a montane belt to a subalpine
zone, though they are widely distributed in a dense thicket of bamboo grass and bushes from a coastal area to an alpine region. In
recent years, on the other hand, they have more frequently bred inhills and lowlands probably because bushy habitat has increased inflood-controlled river basins and abandoned farmland.

Life history
45 6 7 8
breeding season

They build a rugby ball-shaped nest
with an opening on the side or theupper side using primarily deadleaves of bamboo grass (Sasa spp.).
The nest is often built in a low
place of the bushes. In the Myokokogen highlands, Niigata Pref.,north-central Japan, for instance,
they built a nest at a mean height of
54cm (5-140) above the ground inJapanese holly (Ilex crenata), etc.

Photo 2. Nest and nestlings
two days before fledging.

Incubation and nestling periods and fledging rate:

Distribution and Habitat

3Nest:

They usually lay 4-6 eggs, which are chocolate brown in color.

Males sing a loud "Hoh, Photo 1. Japanese Bush Warbler
hokekyo" with the accent[Hiroshi Uchida]on the “ke” of the secondsyllable, and shriek like "Pirrrrrr-kekkyo, kekkyo...", which iscalled "Taniwatari (valley crossing call)". Males also sing thesame song but in a whispering voice when they court females.
Females whisper "Chee, chee" softly during the incubation andnestling periods. Females would call "chatt, chatt", which is named"Sasanaki (bamboo grass call)" in the periods other than incubation and nestling-rearing. Males also utter this "Sasanaki call" inwinter, but not in the breeding season.

2

have maintained a highly developed polygynous system. Although
their mating system is polygyny, a male does not necessarily acquire two females or more at the same time, nor does a femalemate with only one male in a breeding period.

Egg:

Vocalization:

1Uguisu (Jpn) Cettia diphone

910 11 12
non-breeding
seasonBreeding system:

The incubation andnestling periods areabout 15 and 13 days,respectively. The fledging rate is low, such as
27% due largely to predation.

Migration:

Photo 3. Female incubating in a nest.

It is assumed that they move to the lowlands of a temperate region
in winter. But in a population in Mt. Tsukuba, Ibaraki Pref., centralJapan, the same individuals were observed throughout the year(Tojo 1995). On the other hand, the banding records showed that abird moved from Tobishima Island, Yamagata Pref., northern Japan to Ishigakijima Island, south Japan in autumn (Yamashina
Institute for Ornithology 1987) and that a territorial male banded
in May in the Hiki hills, Saitama Pref., central Japan was recaptured in Yokohama, Kanagawa Pref. in November of the sameyear. The populations of higher latitudes probably make a longer
distance migration.

Topics of ecology, behavior and conservation● Brief duration of territory
In many species, the territory is claimed at the beginning of thebreeding season and maintained until its end. In Japanese BushWarblers, however, the territory often changes hands and in shapein a short period of time. Males tend to court any females indiscriminately and spend a long time around females (Fig. 1). Therefore, the moving range of a male changes every day. In addition,
the territory is frequently intruded by males of the neighboring
territories and floater males without a territory, which makes it
difficult to maintain the territory for a long period of time. In theLocations of courtshipsongs sungLocations of every 2.5 min

Japanese Bush Warblers have polygynous mating system. It isknown that a single male breeds with two females or more in histerritory. There is a record of a male that mated with six or sevenfemales one after another in the same breeding season. It is females that build a nest, incubate the eggs and raise the young.
Males try to attract as many females as possible by singing
throughout the breeding season, regardless of breeding stages offemales. It is because females attempt to breed again with othermales after they have fledged their young successfully
or lost their eggs or nestlings due to predation that theyFig. 1. Tracking record of a male with two mates from sunrise to sunset ona day.

♪ http://www.bird-research.jp/1_shiryo/koe/uguisu_040421_kokubunji_mju.mp3♪ http://www.bird-research.jp/1_shiryo/koe/uguisu_0812_hyogo_kaji.mp3

4Mutsuyuki Ueta

Nest

Kyoko Kajimoto

Bird Research News

Vol.4 No.2

2007.2.14. Last Revised: 2014.2.3.

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

バードリサーチ生態図鑑

Myokokogen highlands, for instance, territory holders in a specificperiod represented about 1/3 of the males that lived in the area.
This is another contributory factor to their polygynous matingsystem.

● Vocal communication
Songs of male Japanese Bush Warblers are classified into twotypes. One is a type-H song that sounds as "Hoh-hokekyo" and theother is a type-L song that has intermittent whistles as “Hoh-hohohokekyo”. The type-L song is assumed to function as a threat torivals in the vicinity because territory owners frequently use thistype in the periphery of their territory and they return this type ofsong to replayed songs of other males (Momose 1986).
The "Taniwatari" call is often assumed to be an alarm, but males
sometimes utter this call responding to the "Chee, chee" call of
females, and sometimes start this type of call immediately after thetype-L song, repeating a combination of these song and call for along period of time. In addition, this call is uttered also in theOgasawara Islands where the predatory mammals or snakes do notoccur. It would be better, therefore, not to consider this call torepresent wariness.

● Taxonomic positions of Japanese Bush Warbler
subspecies
Six subspecies of Japanese Bush Warblers are recorded in Japan.
They are C. d. cantans widely distributed in the main islands ofJapan, C. d. diphone of the Ogasawara Islands, C. d. riukiuensis
and C. d. restricta of the Nansei Islands, C. d. sakhalinensis breeding in the south Kurile Islands, and C. d. borealis, an irregular
visitor from the continent (The Ornithological Society of Japan2012).
But the classification is reconsidered now. C. d. restricta was discovered on Minami-daitojima Island and has been regarded to beextinct. However, in recent year, two types of Japanese Bush Warblers were observed on Okinawajima Island and the one with features of C. d. restricta (Kajita et al. 2002). This subspecies is alivein Amami and Ryukyu Islands. The other type observed on Okinawajima Island has characteristics of C. d. riukiuensis, and appears only in winter. Therefore, it probably breeds in the northernarea. C. d. riukiuensis is thought to be a synonym of C. d. cantans
and/or C. d. sakhalinensis. Further, identification of C. d. sakhalinensis and C. d. cantans is unclear, although the former has more
greyish plumage. These subspecies should also be reconsidered.

● Countermeasures against brood parasitism
Japanese Bush Warblers are parasitized byLesser Cuckoos (Cuculus poliocephalus).
The brood parasitism is principally responsible for breeding failure in a nest where theeggs are laid after June when Lesser Cuckoos arrive. Hosts parasitized by other Cuculus cuckoos often eject a parasite egg orabandon their nest, but Japanese Bush Warblers are not reported to reject parasitizedeggs.
In Japanese Bush Warblers, however, they
showed remarkably aggressive responses tothe dummy of the Lesser Cuckoo, and levelsof aggression were higher after the cuckoo
arrived (Hamao 2011). This experimentindicated that Japanese Bush Warblers havecountermeasures before the cuckoos laid
eggs and adaptively adjust their nest defense

Photo 4. Eggs of theJapanese BushWarbler (left) andthe Lesser Cuckoo(right) with aJapanese five-yen
coin (diameter22mm) (above).

behavior in response to theincreased risk of being
parasitized.
Japanese Bush Warblers
start breeding before Lesser Cuckoos arrive in Japanas a summer resident.
Therefore, they can fledge
their nestlings successfully
from the first or second
clutch free from the broodparasitism of Lesser CuckPhoto 5. Japanese Bush Warbler (Cd)oos. The cost of broodattacking a stuffed Lesser Cuckoo
parasitism is reduced by(Cp) placed in front of the nest (N).
starting to breed before thearrival of Lesser Cuckoos. It may be one of the factors that they
have not evolved apparent countermeasures, i.e. egg rejection,
against brood parasitism as in other bird species. Incidentally,
Japanese Bush Warblers are parasitized by Oriental Cuckoos(Cuculus optatus) in Hokkaido, northernmost Japan, where Lesser
Cuckoos are rare.

Literature
Hamao S. 1992. Lack of pair-bond: a polygynous mating system of the JapaneseBush Warbler Cettia diphone. Jpn. J. Ornithol. 40: 51-66. [J+E]
Hamao S. 1997. Japanese Bush Warblers: a polygynous bird. Bun-ichi Sogo Shuppan, Tokyo. [J]Hamao, S. 2011. Seasonal increase in intensity of nest defence against little cuckoos by Japanese bush warblers. Anim. Behav. 82: 869-874.
Hamao S. & Matsubara H. 2001. The first breeding record of the Bush Warbler
Cettia diphone on a flooded bed. Jpn. J. Ornithol. 50: 85-89.
Kajita M., Mano T. & Sato F. 2002. Two forms of Bush Warbler Cettia diphone
occur on Okinawajima Island: re-evaluation of C. d. riukiuensis and C. d. restricta by multivariate analyses. J. Yamashina Inst. Ornithol. 33: 148-167. [J+E]
Momose H. 1986. Function of territory maintenance by vocal communications. In:
Breeding strategies of birds (vol. 2), 127-157. Tokai University Press, Tokyo. [J]The Ornithological Society of Japan. 2012. Check-list of Japanese Birds, 7th revised edition. The Ornithological Society of Japan, Sanda.
Tojo H. 1995. Population dynamics of Japanese Bush Warblers Cettia diphone onTsukuba Cooperative Examination site. Ornithological Society of Japan annual
meeting abstract. 1995: 25. [J]Yamashina Institute for Ornithology. 1987. Bird observation station report. (1987
fiscal year) Yamashina Institute for Ornithology, Abiko. [J]Yoshii T. ed. 1988. Concise dictionary of bird names. Sanseido, Tokyo. [J]Languages of literature cited other than English: [J] in Japanese, [J+E] in Japanesewith English summary.

AuthorShoji HAMAO

Department of Zoology,
National Museum of Nature and Science, Tokyo

I started to study Japanese BushWarblers in 1990 and continue it
now. The subjects are territoriality,
mating system, ecology of insular
populations, songs and anti-parasite
behaviors. The study sites are also
widespread: Niigata, Saitama andKyoto Prefectures, and Izu,
Ogasawara and Amami Islands. In
recent years, I am studying an artificially introduced population inHawaii. Japanese people generally
feel the coming of spring when they
hear elegant warbles of JapaneseBush Warblers. But, for me, theirsongs tell the start of fieldwork
season, and give a tense atmosphere. hamao@kahaku.go.jp

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