Bird Research News

Vol.7 No.8

Asian Stubtail

2010.8.16.

Yabusame (Jpn) Urosphena squameiceps

Morphology and classification
1Classification: Passeriformes Cettidae
Total length:
Wing length:
Tail length:
Culmen length:
Tarsus length:
Weight:105mm♂ 52.7±1.2mm (n = 64)♂ 29.4±1.1mm (64)
♂ 10.4±0.5mm (64)
♂ 19.2±0.4mm (64)
♂ 9.3±0.6g (63)

♀ 51.5±1.2mm (56)
♀ 28.7±0.9mm (56)
♀ 10.3±0.5mm (56)
♀ 19.1±0.6mm (56)
♀ 9.3±0.6g (27)Appearance:
The male and female Asian
Stubtails are similar inplumage coloration. They
are brown all over, but paler
on the underpart than theupperpart. The crown looks
scaly due to the dark edgesof feathers (Photo. 1). They
have a distinct pale brownsuperciliary. After fledging,the juveniles molt into adultPhoto 1. Asian Stubtail. [Ryozo Yamaplumage in a short period ofda]
time, which makes it difficult to distinguish between juveniles and adults by plumage coloration (Kawaji & Hirokawa 1998).

Vocalization:

sound intensity

Once males arrive at the breeding grounds, they sing their cricketlike diagnositc song of "shee-shee-shee-shee" with rising intonation. The common call of the male and female sounds like "Chottchott-chott" as in Winter Wrens. When they are alarmed, they callcontinuously "Bich-bich-bich" or make a metalic sound like
"Chichichittz, chichichittz". Males call in the same way when theyare engaged in a territorial defense.

frequency

2345

678

migration breeding period

The total length after Enomoto (1941), and other measurements by the author. Themale statistically shows significantly larger values in the mean lengths of natural wingand tail. But the difference may not be always distinct (Kawaji 1995).

dBHz
14,00012,00010,000
8,000
6,000
4,000
2,000

91011 12wintering period

Breeding system:
They are basically monogamous, but can be polygamous (Kawajiet al. 1995).

Nest:
Male Asian Stubtails visit the study site (Hitsujigaoka experimental forest, Sapporo, Hokkaido) in late April every year andclaim the territory, singing vigorously at the top of a tall tree for awhile. Some males sing a distinct song at night right after arrival
in some areas (Masayoshi Kamioki pers. comm.). A male has
about 0.5ha singing area on average. The study of the difference inarrival date between the male and female of a pair showed thatfemales arrived about ten days later than males. When a male pairs
up with a female passing through the territory, the male moves
around with the female. About 12 days later, the female begins tobuild a nest and the male starts to sing on the ground, instead of intreetops.
It is females that build a nest. It takes about five days on averageto complete it. They usually build a cup-shaped nest on theground. They lay grass fibers and fallen leaves and animal fur inthe inner cup. They often use fallen leaves with only veins for theexterior. The nest is 54mm in diameter on the inside and 38mm indepth. In the study site of Hitsujigaoka, for instance, they usuallybuild a nest in a space under the fallen leaves lifted from theground by Sasa grass bended under the weight of snow, when thebamboo grass rises again
after the snow has melted.
They sometimes use as anest site the fork of theroots at the base of a large
tree and a hollow on aslope in the woods aswell. There was a pairwhich built a nest in ahollow of a birch tree
trunk at a height of 1.3m
above the ground, which
Photo 2. Nest and eggs
is an exception.

Egg:
02

4

6
8time (second)10

1214Fig. 1. Sonagram of Asian Stubtail song. [Mutsuyuki Ueta]

Distribution and Habitat
Distribution:
As a summer resident, Asian Stubtails visit Japan (to the north ofYakushima Island, Kagoshima Pref., southern Japan). They also
breed in northeastern China, the Korean Peninsula, the Ussuri
region, Sakhalin and the Kuril Islands. They generally migrate tosouthwestern China, Taiwan and the Indo-China Peninsula in winter, but some of them winter in the Amami Islands and the Okinawa Islands as well.

Habitat:In the breeding season, Asian Stubtails are usually found in a
broad-leaved or mixed forest with the under-growth of Sasa spp.
(bamboo grass) or various shrubs and a thick litter layer on theground. They occasionally stop over in parks of urban areas whileon migration.

624♪ http://www.bird-research.jp/1_shiryo/koe/yabusame_060526_tanzawa.mp3
Mutsuyuki Ueta

Life history

Asian Stubtails generally
breed more than once ina breeding period. The
clutch size was six eggs
from every nest in May,but it decreased to 5.4
eggs after June in thestudy
siteof
Hitsujigaoka, Sapporo.
The eggs have red flecks
on a white ground (Photo2). They are 1.5cm by
1cm and about 1g in Photo 3. Nestlings and eggs
weight. During the egglaying period, females
visit their nest and lay an egg early in the morning every day. Afterlaying, however, they leave the nest and do not return until thefollowing morning.

Incubation and nestling periods and fledging success:Completing the clutch, females start incubating immediately, butmales do not take part in the incubation. The incubation and nestl-♪ http://www.bird-research.jp/1_shiryo/koe/yabusame_0906_hyogo_kaji.mp3
Kyoko Kajimoto

Bird Research News

Vol.7 No.8

2010.8.16.

© Japan Bird Research Association
Sumiyoshi 1-29-9, Fuchu, Tokyo, Japaning periods are 13and 10 days, respectively.
Females continue toincubate the nestlings for about
eight days afterhatching.
Whilefemales incubate
the eggs, males
visit the nest exclusively to feed
females only once Photo 4. A pair of Asian Stubtails feeding thenestlings.
or twice a day.
Females leave thenest to feed once an hour for about 20 minutes. After the nestlings
have hatched, males take full responsibility for feeding them,while females brood them except when they occasionally leave thenest to feed. The diet of the nestlings consists primarily of larvaeof lepidoptera (caterpillars), followed by spiders and flies(diptera). The male parent mostly takes care of the fledglings because the female usually attempts the second breeding several days
after the young have fledged. The juveniles learn to forage forfood by themselves about 10 days after fledging. In theHitsujigaoka study site, the hatching success was 89% and fledging success was 80% which was higher than in other areas (Hitoshi
Ohara pers. comm.). The common predators for the Asian Stubtail
are green tree snakes and foxes. But in the study site, few nests fell
victim to carnivorous mammals which may explain the high fledging success in this site. A dense thicket of bamboo grass probably
prevented predatory mammals from gaining access to Asian
Stubtail nests.

Topics of ecology, behavior and conservation● A stranger bird at the nest and what it means
In Asian Stubtails, birds other than the nest owners are frequently
observed at the active nest during the breeding season, for which
the possibility of a cooperative breeding was earlier suggested
because those visiting birds were assumed to be a helper (Ohara &Yamagishi 1984, 1985). Afterwards, however, it turned out that
their breeding system was quite different from a cooperative
breeding. Ohara (1992) reported that visitors were confirmed at alarge number of nests late in the breeding period in the study siteof Nagano Pref., central Japan. More than two adult birds were

バードリサーチ生態図鑑
engaged in raising the nestlings. Those visitors are all males,
which are classified into the following three categories: 1) neighboring males whose partners are incubating the eggs, 2) neighboring males that have lost their partners and 3) unknown males thathave never sung in the neighborhood. In the Hitsujigakoka study
site, on the other hand, birds other than the nest owners were also
observed at 48% of the active nests (Kawaji et al. 1996), which
occurred since the early nestling period of the first breeding. Someof the visitor males had their own nests and their nests were confirmed to be in the stage of incubation. Since the incubation iscarried out only by females, their partners move around and visit
the neighboring pairs' nests, where they occasionally feed the nestlings. The visiting and occasional helping behavior of the neighboring males is assumed to be a strategy to acquire the female
partners of the visited pairs when they fail in their breeding attempts. Most of the visitor males sang vigorously in the vicinity of
the neighboring pair's nest without helping their breeding actively(Photo 5). It is interesting to note, however, that some males chaseafter the territorial males relentlessly or attack them directly. Many
enigmas remain to be solved about the relationship between abreeding pair and an extra-pair male in Asian Stubtails.

Literature
Enomoto Y. 1941. Wild Bird Handbook (Vol. 2). Osaka Chapter of Wild Bird
Society of Japan, [J]Kawaji N. 1995. Validity of sex discrimination of the Short-tailed Bush Warbler
Cettia squameiceps based on morphological measurements. Bull. Jpn. Bird
Banding Assoc.10:18-22. [J+E]
Kawaji N. & Hirokawa J. 1998. Complete post-juvenile moult of the Asian Stubtail
Urosphena squameiceps. Bull. Jpn. Bird Banding Assoc. 13:1-7. [J+E]
Kawaji N., Saitoh T., Ishibashi Y. & Yoshida M.C. 1995. An example of polygynyin the Short-tailed Bush Warbler Cettia squameiceps. Jap. J. Ornithol. 44:93-97.
Kawaji N., Kawaji K. & Hirokawa J. 1996. Breeding ecology of the Short-tailedBush Warbler Cettia squameiceps in western Hokkaido. Jap. J. Ornithol. 45:115.
Ohara H. 1992. The appearance of β & γ males in the nest of the Asian Stubtail:before and after the invasion. Summary of Ornithological Society of Japanannual meeting in 1992: 27 [J]Ohara H. & Yamagishi S. 1984. The first record of helping at the nest in the Shorttailed Bush Warbler Cettia squameiceps. Tori 33:39-41.
Ohara H. & Yamagishi S. 1985. A helper at the nest of the Short-tailed Bush Warbler Cettia squameiceps. J. Yamashina Inst. Ornith. 17:67-73.
Languages of literature cited other than English: [J] in Japanese, [J+E] in Japanesewith English summary.

Author
Noritomo KAWAJI Forestry and Forest Products Research Institute

Photo 5. Arrows show the nest owner male (middle) and female (right) in
the nest and a visitor male (upper left). (From the video image by Masayoshi Kamioki).

I studied the breeding ecology of Asian Stubtails for about six years
when I lived in Sapporo before. While struggling with a dense thicketof bamboo grass in the experimental forest of the office every day I
collected many interesting dataon the species. I did not findany good study sites for Asian
Stubtails after I had left Sapporo. When I returned to Sapporo
after a dozen years and observed breeding Asian Stubtails,
I realized the charm of this bigeyed little bird again. I feel that
Asian Stubtails are still full ofriddles to be solved.
syrmaticus@emobile.ne.jp

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