Bird Research News

Vol.3 No.10

Eastern Spot-billed Duck
Morphology and classification
Classification: Anseriformes Anatidae
Total length: 515-645mm
Tail length:79-102mm
Tarsus length: 41-51mm

Wing length:245-292mm
Culmen length: 45-49mm
Weight:750-1156g

Total length and weight after Kear (2005), and the others after Kobayashi (1985).

Appearance:
Eastern Spot-billed Ducks are dark brown on the upperpart fromthe head to tail. They are tan on the chest and dark brown on theabdomen with dark brown flecks densely scattered. The superciliary is cream yellow and the eye stripe is dark brown. The speculum is metallic dark blue. The outer edge of the tertiary flightfeathers is white. The tip of a bill and the legs are orange yellow,
which are conspicuous in the field.
Males and females are roughly similar in plumage coloration, butdifferent in the color of the the upper and lower tail coverts between the sexes. Males look
black, while females lookbrownish in the upper and lower tail coverts from a distancebecause the individual featherof both tail coverts is black inmales but rimmed with brownin females. When you lookclosely at two Eastern Spotbilled Ducks staying together inthe breeding season and notice
the difference in color between
their upper and lower tail cov- Photo 1. Female of Eastern Spotbilled Ducks.
erts, they may be a pair.

Vocalization:
Eastern Spot-billed Ducks quack "Gwet, gwet", which is similar tothe call of Mallards (Anas platyrhynchos), but carries a greater
distance.

Distribution and Habitat

2006.10.13.

Karugamo (Jpn) Anas zonorhyncha
Egg:
The egg is creamy white with noflecks. The size is 55.5mm by41.6mm and the weight is 44.357.4g (Photo. 3). The clutch size is
10-14 eggs.

Females alone build a nest and incubate eggs. The incubation period is26-28 days. Hatchlings leave thenest immediately after the feathers
dry and follow their female parent.
Juveniles become almost the size of
their parents and start to fly in August, when they form flocks of several dozen birds

The diet of Eastern Spot-billed
Ducks consists primarily of theseeds and leaves of various
plants including rice. Theyglean, filter food out of thewater and feed upside down in
the water depending on thefeeding habitat.
We counted the number ofEastern Spot-billed Ducks andPhoto 4. Eastern Spot-billed Duckstudied their behavior in rice
feeding in a rice field.
fields during the day and nightin the breeding season. The density of the ducks using rice fields
was significantly higher at night than in the daytime (Fig. 1). Of
the behavior, on the other hand, feeding and resting accounted for
67% and 22%, respectively in the daytime, whereas feeding was
94% and resting 3% at night (Fig. 2). This study suggests that
Eastern Spot-billed Ducks use rice fields as a feeding site during
the night with high frequency. In addition, a proportion of two-bird(pair) flocks was higher at night (63%) than in the daytime (41%).

Eastern Spot-billed Ducks are species breeds almost throughout
Japan and is generally a year-round resident south of Honshu (thelargest main island). Banding studies have shown that some birds
migrate to Sakhalin and the Chinese Continent.

0.4Life history
12345 6 7 8 9 10 11 12
breeding season non-breeding season

density birds / ha0.5

Eastern Spot-billed Ducks prefer lowlands and usually occur inlakes, marshes, wetlands, rice fields, tidal flats and rivers. They
nest separately from late April to July in meadows and reed beds
on lakes, ponds and rivers, but they may also breed in a colony inisland-like places such as sandbars in a river. In the wintering period, they are found in most bodies of water, such as lakes, marshes,ponds and rivers. They also form a flock with Mallards in littoral
regions.

Photo 3. Eggs of Eastern Spot-billed Ducks

Diet and foraging behavior

Distribution:Habitat:

Photo 2. Nest of Eastern Spot-billed Ducks

Incubation and nestling
periods:

unknown
day n =396

feeding

resting

0.3
0.2

night n =510

0.1
0.0

daynightFig. 1. Densities of ducks
using rice fields by
day and night.

0%

20%

40%

60%

80% 100%

Fig. 2. Proportion of behaviors by day andnight.

Topics of ecology, behavior and conservation● Infanticide of females

They build a plate-shaped nest using herbs, bamboos, reeds anddead grass. The nest has a diameter of 22-30cm on top and 1520cm at the base and is 8-12cm in depth (Photo. 2).

As a peculiar behavior, there is a record of infanticide committed
by a Eastern Sopt-billed Duck female in the breeding season(Shimada et al. 2002). In Yatsu tidal flat, Chiba Prefecture, central
Japan a female with one young attacked and killed eight ducklingsof another Eastern Spot-billed Duck and three ducklings of a Gadwall (Anas strepera). It is assumed that the parent birds of Eastern♪ http://www.bird-research.jp/1_shiryo/koe/karugamo_0910_hyogo_kaji.mp3♪http://www.bird-research.jp/1_shiryo/koe/karugamo_0806_hyogo_kaji.mp3

Nest:

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Kyoko Kajimoto

Kyoko Kajimoto

Bird Research News

Vol.3 No.10

2006.10.13.

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

バードリサーチ生態図鑑

Spot-billed ducks more frequently show aggression toward otherducks and therefore commit infanticide in urban areas where they
are forced to breed close together due to a short supply of nestingsites.

● Relationship between Eastern Spot-billed Ducks and Mallards
It is said that Mallards and Eastern Spot-billed ducks are ecologically equivalent species because they are similar in morphologyand behavior. Observations showed that one of these species wassometimes taken into a larger flock of the other species when there
was a marked difference in flock size between the two duck species. When more than several dozen birds congregate, on the otherhand, the two species did not form a mixed flock, but maintained
single-species flocks. In Lake Izunuma (2.89km2), Mallards andEastern Spot-billed Ducks were separately distributed in the western and eastern part of the marsh, respectively. In ponds of small
urban parks, dominant duck species vary from one pond to another. For instance, the density of Mallards was low in a pond withthe high density of Eastern Spot-billed Ducks and vice versa,
which shows that there is an inverse proportion in density between
the two species.

● Conservation issues
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Damage rate (%)

Eastern Spot-billed Ducks
cause damage to the farmingin the breeding season in theTohoku region, northern
Japan. They eat paddies sownin flooded rice fields or reduce rice germination rate bytreading on the surface ofrice fields. Research showedthat the density of Eastern
Spot-billed Ducks was highin the vicinity of human settlements, where hunting pressure was low, and the rate ofagricultural damage became
higher in proportion to theirdensity (Fig. 3). The hazard
map of the agricultural damage inflicted by Eastern Spotbilled Ducks has been madebased on this result (Fig. 4).
It is predicted that humanactivities have a great effecton the number of surface
feeding ducks taking a rest in
the daytime, such as Eastern
Spot-billed Ducks, Mallardsand Teals (A. crecca) in thesmall ponds of urban parks inthe wintering season. Since
surface feeding ducks are
assumed to need the corearea of a pond for safety
from terrestrial predators, weused Eastern Spot-billed
Ducks as a representative
species and calculated thesafe area of ponds (Shimada2001). The safe area was'total pond area' minus'escape distance multiplied

25201510500246810121416

density (birds / km 2 )Fig. 3. Relationship between the density of Eastern Spot-billed Ducks
and their damage rate. The damagerate and density were based on aquestionnaire survey and a fieldstudy, respectively. The damage
was surveyed in the rice fields
where no preventive measures
were taken against Eastern Spotbilled Ducks.

Expecteddamage rate (%)
20%<
15～20%
10～15%
5～10%
0～ 5%
0%

Fig. 4. Hazard map of agricultural
damage by Eastern Spot-billed
Ducks A square is 5 by 5 km.

by the shoreline length that humans have easy approach', where
escape distance is the distance that ducks flee from humans. We
calculated two levels of the distance from the shore as ca. 10m in apond with artificial feeding and ca. 30m in a pond without feeding.
The number of ducks was significantly correlated with the safetyarea, though no significant correlation was detected between thenumber of ducks and the whole area of a pond. This analysis suggests that the safety of a pond (distance from humans) plays amajor role in the habitat selection of surface feeding ducks.
Eastern Spot-billed Ducks are one of the most familiar ducks toJapanese people, but their ecology has only partially been known.
Although they are commonly found in Japan, it is necessary to
study them more earnestly considering they are distributed in theFar East alone.

Literature
Azuma A., Tsuji K., Okuyama T. & Sato T. 2004. The living state and the associated factors of the Eastern Spot-billed Duck in the rice field areas of Tohoku
region. The annual meeting of the Ornithological Society of Japan 2004. Summary. 71. [J]Azuma A. & Kumagai T. 2005. Difference of the number and behavior by day andnight of the Eastern Spot-billed Duck in the breeding period in the rice fieldareas. The annual meeting of the Ornithological Society of Japan 2005. Summary. 93. [J]Kear J. 2005. Ducks, Geese and Swans, volume 2. Oxford University Press, Oxford.
Kiyosu Y. 1966. Dictionary of Wild Bird. Tokyo-do Pub., Tokyo. [J]
Kobayashi K. 1985. 1985. Illustrated Guide to Japanese Birds. Hoikusha, Osaka. [J]Kuroda N. 1939. Ducks and Geese. Shukyosha-shoin, Tokyo. [J]Kumagai T. 2005. On the ecology and density relative to the surrounding environment of the Eastern Spot-billed Duck in rice field: on the crop damage avoidanceby hazard map. The University of Iwate graduation thesis, Morioka. [J]Sato T. & Azuma A. 2003. The analysis of the crop damage by the Eastern Spotbilled Duck on the direct sowing into flooded paddy in Tohoku region by questionnaire survey. Journal of Rural Planning Association5:13-18. [J+E]
Shimada T. 2001. Roosting of ducks on open water: resting site selection in relation
to safety. Japn. J. of Ornithol. 50:167-174.
Shimada T., Kuwabara K., Yamakoshi S. & Shichi T. 2002. A case of infanticide inthe Spot-billed Duck in circumstances of high breeding density. J. of Ethol. 20:87-88.
Languages of literature cited other than English: [J] in Japanese, [J+E] in Japanesewith English summary.

AuthorTetsuo SHIMADA
Atsuki AZUMA &Toru KUMAGAi

The Miyagi Prefectural Izunuma-Uchinuma
Environmental Foundation
Department of Agriculture, Iwate University

I studied ducks including Eastern Spot-billed Ducks in the Tokyo Bay
area of Chiba Prefecture. I met Azuma, one of the coauthors throughthe study of Eastern Spot-billed Ducks. They are one of the ducks inwhich I have been interested since I moved to Lake Izunuma. I always
look at them, searching for some interesting study topics on them.
(Tetsuo Shimada)tshimada0423@gmail.com
Since 2001 we have worked on making the "hazard map of Eastern
Spot-billed Duck damage to paddy fields based on their population
study" as a part of the research commissioned by the Ministry of Agriculture and Forestry. Last
year we made the hazard mapof Eastern Spot-billed Duckdamage to rice farming in theTohoku region based on thestudy of their density andbehavior. We would like tocarry out a more detailed
study on the life of this species through the year, if givena chance. (Atsuki Azuma &From left, Kumagai, Shimada and Azuma. Toru Kumagai)

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