Bird Research News

Vol.7 No.5

Eastern Marsh Harrier

2010.5.20.

Chu-hi (Jpn) Circus spilonotus

Morphology and classification
Classification: Accipitriformes Accipitridae♂ 480mm380-430mm
215-262mm
85-91mm

Total length:
Wing length:
Tail length:
Tarsus length:♀ 580mm
Wingspan:1132-1372mm
Culmen length: 28-31mm
Weight:498-844g

Measurements after Enomoto (1941).

Appearance:
The plumage coloration of Eastern Marsh Harriers is basicallybrownish, but varies considerably (Morioka et al. 1995). Thereare types such as totally darkbrown, off-white from the headto the leading edge of a wing,
and pale brown with a verticalstriped underpart, bluish graywing coverts and ashy brown Photo 1. Eastern Marsh Harrier.
rectrices. Although these varia[Michio Kobori]tions are thought to be related tothe differences of individuals, sexes, ages and breeding grounds,
the detail is still unknown.
Eastern Marsh Harriers meow like "Mibyaa, mibyaa", when another harrier approaches their territory. They also threaten each otherin dispute or other birds of prey, letting out a shriek like "Kyakkyak-kyak-kyak". In addition, males call "Kuwe, kuwe" during theaerial display in the breeding period.

Distribution and Habitat
Distribution:
Eastern Marsh Harriers breed in the area from Lake Baikal to theUssuri region, Mongolia, northeastern China and Japan, and migrate to Japan, Taiwan, Borneo, the Philippines, Southeast Asiaand southern China in winter.

Habitat:
They occur in the vast reed bed of the coastal reclaimed land, large
lakes and marshes, and the lower reaches of a large river.

Life history
23Nest:They build a nest in wet reed beds or the dry tall grassland of Japanese pampas grass (Miscanthus sinensis), etc., piling up dry grasson the ground (Nishide 1979, Tada 2007, Naya et. al. 2007, Chiba2008). The nest size is about 110-130cm by 80-90cm (Chiba 2008,Naya et al. 2007).

Egg:
They lay an egg at 3.3 day intervals on average (Nishide 1979).
The clutch size is 4-7 eggs (Chiba 2008, Nishide 1979). The egg
size is 48.0mm by 38.0mm on average (n = 5) (Chiba 2008). Theegg color is grayish white (Chiba 2008).

Incubation and nestling periods:
Females mostly incubate eggs. The incubation period is about 2834 days (Chiba 2008). Males primarily hunt during the breeding
period (Nishide 1979). The young leave the nest about 28 days
after hatching (Nishide 1979). According to the study conducted in
the vicinity of Lake Baikal, Russia, 27-43% of the eggs fledged（Fefelov 2001）.

Roost and roosting behavior:

Vocalization:

1still undiscovered nesting grounds in Hokkaido in particular. The
total population of the species wintering in Japan, on the other
hand, has not been counted except for the roosting number of someareas, such as Watarase Marsh, Tochigi Pref., central Japan.

4 5 6 7
breeding season

In Watarase Marsh,Tochigi Pref., central
Japan, Eastern MarshHarriers use as a roostsite a sparsely-grownreed or Miscanthus
sacchariflorus bed withthe dense undergrowthof 30-50cm sedges andgrasses (Hirano et al.
1998). There are manyspots
withbendedPhoto 2. Roost site of Eastern Marsh Harriplants in the roost siteers.
because they stomp andcrouch to sleep on the ground at night (Photo 2).
They usually return to the roost 20 or 30 minutes after sunset in theevening and leave there about 20 minutes before sunrise in themorning (Hirano et al. 1998).

Diet and foraging behavior
8 9 10 11 12
non-breeding season

Breeding system:
Eastern Marsh Harriers are generally monogamous, but some ofthem are polygamous. Though no polygamous breeding has beenrecorded in the vicinity of Lake Baikal, Russia, a single case ofpolygamy was reported from Sakata, Niigata Prefecture, central
Japan (Chiba 2008).
In the breeding grounds, they start aerial displays as early as
March, when they form a pair. They lay eggs in mid-April to May
and fledge the young in July. They arrive at the wintering grounds
around October and establish their own territory, but form a communal roost at night.

Population:
The number of Eastern Marsh Harriers breeding in Japan is estimated to be 60 pairs (Ura 2010). It is assumed, however, that thebreeding population is somewhat larger because there are probably

There is only fragmentary information about the diet of Eastern
Marsh Harriers during the breeding period in Japan. Chiba (2008)
reported that they frequently hunted mice and occasionally captured larks in Sakata, Niigata Pref.. In the vicinity of Lake Baikal,Russia, voles and small birds accounted for 80% and 20% of thediet, respectively (Fefelov 2001). In Watarase Marsh, on the otherhand, their diet included large birds (38.6%) such as ducks, medium-sized birds (4.7%) such as Brown-eared Bulbuls (Hypsipetesamaurotis) and thrushes, small birds (9.4%) such as Tree Sparrows(Passer montanus) and Skylarks (Alauda arvensis), medium-sizedmammals (2.8%) such as weasels, small mammals (31.9%) such asvoles and shrews, and fish (1.7%) (Hirano et al. 2006).
They adopt several foraging methods. For instance, they suddenly
turn around and dive at the prey when they detect it near theground, while making slow search flight over the reed bed (socalled surprise attack). They snatch the prey from other birds ofprey (piracy) and also scavenge for carrion.

4♪ http://www.bird-research.jp/1_shiryo/koe/tyuhi_100406_watarase.mp3
Toshiaki Hirano♪ http://www.bird-research.jp/1_shiryo/koe/chuhi_080110_watarase_hirano.mp3
Toshiaki Hirano

Bird Research News

Vol.7 No.5

2010.5.20.

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

バードリサーチ生態図鑑

Topics of ecology, behavior and conservation● Feeding habitat in winterThe wintering habitatof Eastern Marsh Harriers is a vast reed bed(Photo 3), but what
components of a reed
bed are vital to theirhunting?
We studied the frequency of their searchflight in the open areaof burnt reed bed andthe adjacent intact reed Photo 3. Wintering habitat of the Eastern
Marsh Harrier in Watarase Marshbed of Watarese Marshin the winter of 2000 (Hirano et al. 2003). The result showedthat the search flight frequency was significantly greater in thereed bed than the open ground (Fig. 1). This suggests the importance of intact reed beds for the foraging harriers. I also studied the search flight frequency in an area with man-made floating islands covered with vegetation and an open water area ofLake Yanaka in Watarase Marsh. The result showed that harriers
frequently used the area with the islands as a hunting site, but
hardly ever flew over the open water area (Hirano 2005).

frequency of use

700

Study site I160

Study site II

140600120500100400803006020040100020

intact burnt
BA
2001

B'A'
2002

0intactburnt
AB
2001：observed value

A'B'
2002

：expected value

Fig. 1. Comparison of harrier foraging frequencies between the intact andthe burnt reed beds. The foraging frequency was significantly higher in
the intact reed beds (A) than in the burnt reed beds (B) in 2001 in bothstudy sites of I and II, but the difference was not apparent one year
later in 2002.

In addition, I studied the search flight frequency in an artificial
reed bed with variety of habitats such as ponds, waterways andmanagement roads and an adjacent dry reed bed (Hirano 2008).
The result showed that harriers used the diverse reed bed withsignificantly higher frequency than the dry reed bed in two wintering periods (Fig. 2). I partitioned a reed bed with ponds andwaterways into 100m by 100m squares to compare the search
2004/2005→Literature
Chiba A. & Sato G. 2008. On the breeding of the Eastern Marsh Harrier Cirucus
spilonotus in the Sakata of Niigata City. Strix 26:81-95. [J+E]
Enomoto Y. 1941. Wild Bird Handbook. Osaka Chapter of Wild Bird Society ofJapan, [J]Fefelov IV. 2001. Comparative breeding ecology and hybridization of Eastern andWestern Marsh Harriers Circus spilonotus and C. aeruginosus in the Baikal
region of Eastern Siberia. Ibis 143:587-592.
Higuchi K., Hirokawa J. & Hamada T. 1999. The breeding situation of the Eastern
Marsh Harrier Circus spilonotus spilonotus in the lower reaches of the Ishikari
River valley, Hokkaido. J. Yamashina Inst. Ornithol. 31:103-107. [J+E].
Hirano T. 2005. The effects of vegetated artificial islands on the habitat use ofhunting Eastern Marsh Harriers. Bird Research 1:A15-A23. [J+E]
Hirano T. 2008. The Habitat use of hunting Eastern Marsh Harriers wintering inWatarase Marsh. Bird Research 4:A9-A18. [J+E]
Hirano T., Endo K., Kimijima M., Kobori S., Nonaka J. & Uchida H. 1998. The
Eastern Marsh Harrier's roost in Watarase Marsh of autumn-winter period. Strix
16:1-15. [J+E]
Hirano T., Kimijima M. & Kobori S. 2003. On the impact of the wild fire on theEastern Marsh Harrier's feeding behavior in winter. Strix 21:71-79. [J+E]
Hirano T., Koike I. & Tsukahara C. 2005. Food habits of Eastern Marsh Harriersand Hen Harriers wintering at Watarase Marsh, central Japan. Jpn. J. Ornithol.
54:29-36. [J+E]
Morioka T., Kanouchi T., Kawada T. & Yamagata N. 1995. Japanese Hawks andEagles. Bun-ichi-sogo-shuppan, Tokyo. [J+E]
Nishide T. 1979. Breeding record of the Eastern Marsh Harrier in Hachirogata
reclaimed land. J. Yamashina Inst. Ornithol. 11:109-120. [J]Naya H., Koumizu G. & Shimizu T. 2007. Breeding confirmation of the Eastern
Marsh Harrier in Osaka Prefecture. Strix 25:99-103. [J+E]
Tada H. 2007. The breeding record of the Eastern Marsh Harrier in Hotokenuma
March. Strix 25:87-93. [J+E]
Ura T. 2010. On the Eastern Marsh Harrier. Ura ed. in "The breeding and otherranges of the Eastern Marsh Harrier of the different areas of Japan": Harriersummit 2010. Mie Chapter and Aichi Chapter of Wild Bird Society of Japan,
and Bird Survey Group of Nagoya. Wild Bird Society of Japan, Tokyo. [J]Languages of literature cited other than English: [J] in Japanese, [J+E] in Japanesewith English summary.

AuthorToshiaki HIRANO Japan Bird Research Association

2006/2007

NSite B

Site A
0 100ｍ Frequency of foraging flight.
highflight frequencies. They used the squares including ponds andwaterways with significantly higher frequency than those withvegetation alone.
These results suggest that a tall reed bed is vital for the huntingof Eastern Marsh Harriers, but it is not sufficient. They also need
a complex habitat composed of diverse components, such asponds, marshes and narrow waterways because complex reed
beds attract their major prey, such as ducks and are highly suitable for their usual hunting technique referred to as “surpriseattack”. It is extremely important, therefore, to create and conserve diversified reed beds comprised of various elements, suchas ponds, marshes and narrow waterways to conserve harriers
including Eastern Marsh Harriers.

UninvestigatedlowFig. 2. Comparison of harrier foraging frequencies between reed beds witha complex (site A) and a simple structures (site B)

I have recently spent most of the year studying birds in Watarase Marsh, Tochigi
Prefecture, central Japan. Especially theseseveral years I have focused on the population statuses of crakes, Eurasian Bitterns
and Japanese Marsh Warblers instead of
the wintering ecology of the harriers. Inorder to collect the basic information whichis instrumental to making Watarase Marsha true paradise for marshland birds, I walkaround the marsh in the darkness before
sunrise rubbing my drowsy eyes.

5