Bird Research News

Vol.10 No.11

2013.11.29.

Japanese Marsh Warbler

Breeding system:

Morphology and classification
Classification: Passeriformes Locustellidae
Total length:
Wing length:(*)
Tail length:
Tarsus length:
Culment length:
Weight:

Oh-Sekka (Jpn) Locustella pryeri♂ 126 ± 4mm♀ 119 ± 4mm♂ 53.3 ± 1.0mm♀ 48.8 ± 1.4mm♂ 57.6 ± 1.6mm (n = 30) ♀ 52.2 ± 1.2mm (24)
♂ 51.3 ± 2.8mm♀ 48.1 ± 3.8mm♂ 20.1 ± 0.5mm♀ 18.9 ± 0.4mm♂ 10.6 ± 0.4mm♀ 10.1 ± 0.5mm♂ 14.5 ± 0.8g
♀ 12.6 ± 1.5g

Measurements in the Tone River from the Yamashina Institute for Ornithology(1988). * is measured by the author in Hotokenuma area. Males are larger than females. Male and female sizes vary between breeding grounds. Males and females of
Hotokenuma area, northern Japan are larger (especially longer in wing length) thanthose of the Tone River, central Japan.

Appearance:
Males and females are similar in plumage coloration. They are dark brownon the upperpart and white on the underpart. They have a light superciliary
and black flecks on the back and thetertiary flight feathers. There is nodifference in plumage coloration between the breeding birds of Hotokenuma and Tone River (Takahashi et al.
2010).

Japanese Marsh Warblers are polygamous. The study on the mating system in Hotokenuma revealed that 40% of the pairs wasmonogamous, 30% of the males was unpaired and 30% of themales was polygynous, where a male paired with up to five females (Takahashi 2013). Some females breed twice in the same
season. Only females are responsible for nest-building and incubation. It is not confirmed that males feed their partner during theincubation period. Females alone incubate their nestlings, but boththe male and female feed the nestlings. Males that has two or more
breeding nests simultaneously feed only their young of a nest at
the most advanced breeding stage.

Nest:Females usually build a nest at the base of a reed and Japanese
pampas grass (Miscanthus sinensis), using dry reed leaves andgrass. The nest includes three different types. A nest of type I is
cup-shaped (11.7cm in depth on average). Type II is dome-shaped
without decorations (11.4cm in depth). Type III is also domeshaped but decorated with live grass (17.4cm in depth) (Nishide1975, Takahashi et al. 2013; Fig. 1). The type of a nest is closely
related to the nesting habitat. Type II is built in a damp site with alarge amount of dry grass, while type III is seen in a dry site with
abundant live grass. Type I is found in the intermediate habitat or asite lacking undergrowth.

Vocalization:
In the breeding period, males sing in a
thick voice like "bijo-bijo-bijo-bijo" or"Chori-chori-chori", often with "Je-jeje" as a prelude. Males frequently flyup singing several meters from thegrass for a few seconds, which iscalled a song flight (Photo. 2). They
call like "Gi-gi" or "Gi-ch-ch. "タイプ
Type1I

タイプ2 IITypeタイプ
Type 3III

Photo 1. Japanese MarshWarbler (Above) andsong flight of a Japanese Marsh Warbler(Below) [Akio Miya]

Distribution and Habitat
Distribution:
Japanese Marsh Warblers are classified into two subspecies.
Nominotypical subspecies Locustella pryeri pryeri is locally distributed in Japan alone, while subspecies L. p. sinensis is distributed in China, the Korean Peninsula and Far East Russia (Shigeta1991, Morioka & Shigeta 1993). In Japan, L. p. pryeri breeds inthe Hachirogata reclaimed land, Akita Pref., Watarase Marsh,Tochigi Pref., Lake Kasumigaura, Ibaraki Pref., but most of themconcentrate in Hotokenuma area and the Iwaki River, AomoriPref., and the Tone River, Ibaraki and Chiba Prefs. (Ueda 2003).
They winter on the Pacific seaboard of the Tohoku, Kanto andTokai regions, and as of 2013 the northernmost wintering groundis the southern coast of Iwate Pref. (Chiba & Sakuyama 2011).

Habitat:Japanese Marsh Warblers occur in wet grassland and reedbeds,
such as riverbeds, lakefront and abandoned rice fields. In thebreeding period, males are known to prefer low moor with abundant sedges in the lower layer, thinly vegetated with low reed in
the upper layer. (Fujita & Nagata 1997, Nakamichi & Ueda 2003,Mikami 2012).

Life history
12wintering
period34migration

5678

breeding period

91011 12migration

Fig. 1. Schematic diagrams and photographs of three types ofnests. Created based on Takahashi et. al. (2013).

Egg:Females usually lay an egg per day in the early morning. The
clutch size is 4.5 ± 0.8 eggs on average with a range of 2-6 eggs
(Takahashi 2013). The egg is white and without flecks.

Incubation and nestling periods and breeding success rate:
Both incubation and nestling periods are approximately 12 days.
Parent birds feed their young up to 18 days after fledging(Takahashi 2013). Nesting success rate (successful nest number/
observed nest number) is comparatively high for a small songbird.
For instance, it was 78.6% in Hachirogata (Nishide 1975) and82.0% in Hotokenuma (Takahashi 2013). Breeding success rate
(fledgling number/egg number) is also high and was 75.8% in
Hotokenuma (Takahashi 2013).

Migration:
Japanese Marsh Warblers are a nomadic bird that moves only
within Japan. Birds breeding in the northern part of the Tohoku
region (the northernmost Honshu) winter in the southern part of
the Tohoku and the Kanto regions. Birds breeding in northern
Kanto either stay in the breeding grounds as a year-round residentor go south to the Tokai region (central Japan) to overwinter(Nagata 1997).

4♪ http://www.bird-research.jp/1_shiryo/koe/oosekka_070424_watarase_hirano.mp3
Toshiaki Hirano♪ http://www.bird-research.jp/1_shiryo/koe/oosekka_081216_watarase_hirano.mp3
Toshiaki Hirano

Bird Research News

Vol.10 No.11

2013.11.29.

© 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

not been confirmed, and it is on the increase as before. (As of Nov.
2013)

Japanese Marsh Warblers are insectivorous. Parent birds feed thenestlings spiders as well as insects, such as lepidoptera, orthoptera,odonata and diptera (Japanese Marsh Warblers’ Habitat ResearchGroup 1995).

Topics of ecology, behavior and conservation● Infanticide of a neighboring maleIn the study site of Hotokenuma, the male of a neighboring territory intruded into the territory that lost its owner and picked thenestlings left behind out of the nest (infanticide behavior), when amale parent disappeared during the breeding attempt (Takahashi2013). This is assumed to be adaptive behavior for the male thatcommitted infanticide because (1) he can conserve food resourcesin a territory to be his own and (2) he can gain an opportunity tobreed with the female left behind.

● History from description as a new species to the recent
population increase

bird number

Japanese Marsh Warblers are designated as an endangered species
and one of the National Endangered Species of Wild Fauna andFlora (protected by so-called the Endangered Species PreservationAct) in Japan, and as a Near Threatened Species by the International Union for Conservation of Nature (IUCN). They were described as a new species based on the individual collected in Tokyo (Seebohm 1884), but they were called a "phantom bird" because their breeding area was not discovered for lack of subsequent observation. The first breeding of this species was confirmed
in 1936 in Gamo, Miyagi Pref., northern Japan (Takeya 1938). But
the birds ceased to breed there within several years, disappearing
again. Many of the present breeding grounds were discovered fromthe 1970s to the 1980s (Nagata 1997). Japanese population of thisspecies was estimated to be about 1,000 and 2,500 birds in 1993
(Kanai & Ueta 1994) and in 2001 (Ueda 2003), respectively. It isconsistently on the increase. Especially, in Hotokenuma, with thelargest breeding population of Japanese Marsh Warblers in Japan,
they have been rapidly increasing in recent years. In 2009, forinstance, there were estimated to be approximately 1,130 birds(based on the counted male number and the assumption that a sex
ratio is 1:1). The population increased by a factor of about sevenbetween 1982 and 2009 (Takahashi et al. 2010; Fig. 2). This population increase can be attributed to (1) the expansion of a vegetation area suitable for breeding Japanese Marsh Warblers in thereclaimed land at the center of Hotokenuma area (Mikami &Takahashi 2013) and (2) increase of wet grassland suitable for
their breeding due to the abandonment of rice cultivation in thesurroundings of the reclaimed land (Narita et al. 2007). It wasconcerned that the breeding population might decrease in thenorthern part of the Tohoku region including Hotokenuma because
many of the wintering and stopover sites were lost or degraded on
the Pacific sea700
board of the Toho559 564
600
ku and Kanto re500
446
gions in the wake
380
400
328
of the Great Toho298 319
256300
ku Earthquake and172
200
Tsunami in March
100 7911, 2011. Howev0er, the impact on
the Japanese Marsh
Warbler population Fig. 2. Change of the abundance of male Japanese Marsh Warblers breeding in Hotokenuma
breeding in thearea. Based on Takahashi et al. (2010).
Tohoku region has

Literature
Chiba K. & Sakuyama M. 2011. The first record of the Japanese Marsh Warbler
Locustella pryeri wintering in Iwate Prefecture, northern Japan. Strix 27: 89-96.
[J+E]
Fujita G. & Nagata H. 1997. Preferable habitat characteristics of male Japanese marsh
warblers Megalurus pryeri in breeding season at Hotoke-numa reclaimed area,northern Honshu, Japan. J. Yamashina Inst. Ornithol. 29: 43-49.
Japanese Marsh Warblers’ Habitat Research Group. 1995. Breeding status and habitatof Japanese marsh warblers at Hotoke-numa reclaimed area. Toyota Foundation
citizens research contest promotion research No.6. No.6C-031. [J]Kanai Y. & Ueta M. 1994. The present distribution and habitat of Japanese MarshWarblers. Survey of the Status and Habitat Conditions of Threatened Species,
1994. Environment Agency, Tokyo. [J]Mikami O.K. 2012. Habitat selection of the Japanese Marsh Warbler Locustellapryeri in a breeding season at Hotokenuma wetland. J. Yamashina Inst. Ornithol.
43: 153-167. [J+E]
Mikami O.K. & Takahashi M. 2013. The Change in the Distribution of Five Grassland Birds Depends on the Change in the Vegetation: a Comparison between 1998
and 2010 at Hotokenuma, Aomori Prefecture, Japan. J. Yamashina Inst. Ornithol.
44: 67-78. [J+E]
Morioka H. & Shigeta Y. 1993. Generic allocation of the Japanese Marsh Warbler
Megalurus pryeri (Aves: Sylviidae). Bull. Nat. Sci. Mus. Ser. A (Zoology) 19: 3743.
Nagata H. 1997. Present status of the Japanese Marsh Warbler (Megalurus pryeri)
and its conservation. J. Yamashina Inst. Ornithol. 29: 27-42. [J+E]
Nakamichi R. & Ueda K. 2003. Recent status and habitat preference of the Japanese
marsh warbler at Hotoke-numa marsh, northern Honshu, Japan. Strix 21: 5-14.
[J+E]
Narita A., Sekishita H & Miya A. 2007. Status and habitat of the Japanese MarshWarbler at Hotoke-numa wetland. Annual report of Oosekka-land 1: 21-27. [J]Nishide T. 1975. Survey of Japanese Marsh Warbler Megalurus pryeri in Hachirogata
reclaimed land, Akita Pref. 1. Habitat distribution and breeding. J. Yamashina Inst.
Ornithol. 7: 681-696. [J+E]
Seebohm H. 1884. Further contributions to the ornithology of Japan. Ibis 2:30-43.
Shigeta Y. 1991. Identification guide 2. The Japanese Marsh Warbler: Birds with avestigial claw on the wing Animals of Japan. 5: 48-51. [J]Takahashi M. 2013. Population dynamics and breeding habitat selection in the Japanese Marsh Warbler Locustella pryeri: Identification of selection factors at multiple spatial scales. Doctoral thesis. Rikkyo University. [J]Takahashi M., Morimoto G., Ebina J. & Miya A. 2010. A preliminary note on plumage coloration in the Japanese Marsh Warbler Locustella pryeri: A comparison
between two local populations. J. Yamashina Inst. Ornithol. 42: 102-106.
Takahashi M., Aoki S., Kamioki M., Sugiura T. & Ueda K. 2013. Nest types andmicrohabitat characteristics of the Japanese Marsh Warbler Locustella pryeri.
Ornithological Science 12: 3-13.
Takahashi M., Miya A., Tsumagari T. & Furukawa H. 2010. Status and habitat of theJapanese marsh warbler at Hotoke-numa wetland in 2007-2009. Annual Report of
Oosekka-land 2: 10-16. [J]Takeya H. 1938. Japanese Marsh Warblers breeding in Gamo. Yacho. 5 (8): 832-840;
5(9): 910-917. [J]Ueda K. 2003. Recent status of the Japanese Marsh Warbler in Japan. Strix 21: 1-3.
[J+E]
Yamashina Institute for Ornithology. 1988. Bird Banding Manual (Identification
No.5). Yamashina Institute for Ornithology, Abiko. [J]Author
Masao Takahashi (NPO) Oosekka-land

2009

2008

2007

2006

2005

2004

2003

2001

1992

1982

I studied the breeding ecology
and conservation of JapaneseMarsh Warblers in Hotokenuma
area, for six years, when I wasenrolled in a doctoral course ofRikkyo University. These days I
am also studying the relationshipbetween birds and art as well as
the conservation of Japanese
Reed Buntings and Swinhoe's
Rails. I have been engaged in theReintroduction Program of Crested Ibises as an associate assistantat the Crested Ibis & Nature Reproduction Research Center of Niigata
University since September 2013 when I moved to Sado
Island, Niigata Pref.. hachi77vanellus@yahoo.co.jp

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