Bird Research News

Vol.7 No.6

Japanese Cormorant

2010.6.24.

Umi-u (Jpn) Phalacrocorax capillatus
Life history

Morphology and classification

1Classification: Suliformes Phalacrocoracidae
Total length:
Wing length:
Culmen length:Bill depth:
Tarsus length:
Tail length:
Weight:800-865mm
315.9 ± 8.9mm (N = 7)
♂ 69.8 ± 1.3mm (12) ♀ 62.0 ± 2.3mm (15)♂ 15.1 ± 0.7mm (12) ♀ 13.2 ± 0.6mm (15)66.9 ± 4.4mm (7)150.7 ± 6.9mm (6)♂ 3.1 ± 0.2kg (42)
♀ 2.5 ± 0.2kg (37)

Culmen length, bill depth, and body weight are taken from the breeding population ofTeuri Island, Hokkaido, and wingspan, tarsus and tail lengths are measured from bycaught individuals in Hamamasu, Hokkaido (Watanuki et al. Unpubl.). The total
length after Enomoto (1941).

Japanese Cormorants are black allover except in the bare skin from theperiphery of the eyes to the throat,
which is yellow. They develop whitefeather patches at the base of the leg
as well as from the head to the neckduring the breeding season. JapaneseCormorants are slightly larger thanGreat Cormorants and their plumage
Photo 1. Japanese Cormohas a greenish sheen. The yellowrants [Photo. Motohiro Ito]bare skin cuts into the throat in a Vshape for Japanese Cormorants, while the boundary of the bareskin with the throat is straight for Great Cormorants.
Japanese Cormorant juveniles (less than one year of age) are whitefrom the breast to the belly, but they begin to grow dark featherson the breast the following year. Young birds of two years or overare dark brown all over, but still have white feathers in places onthe breast (Takano 1982, Juou-cho 2000). Japanese Cormorants
have adult plumage at the age of 3 or over, but there is a breeding
record of birds which have a dark brown breast with white feathersin places (Hayashi 1996).

Vocalization:
Japanese Cormorants rarely call. They utter "Guarr", when people
come close to the nest.

Distribution and Habitat
Distribution and Population:
Japanese Cormorants are distributed only in the Far East. In Japan,
they breed north of central Honshu, mostly in Hokkaido. In theAsian continent, they breed from the Korean Peninsula to Primorskii, Russia. They move south to winter. In Japan, they winter as
far as Okinawa Pref., southern Japan. The breeding populations areestimated to be 5,000 birds along the coast of the Sea of Okhotsk,
8,000 birds in the Kuril Islands, 3,000 birds along the coast ofPrimorskii and 1,000 birds in the Sea of Japan (Siegel-Causey &Litivinenko 1993). In Japan, the breeding populations were estimated to be 1,000 birds in Hokkaido and 100 birds in Honshu(Hasegawa 1984). More recent estimate is that, more than 3,000pairs bred in Hokkaido in the 2000s,and they are on the increase (Osa &Watanuki 2002).

Habitat:

44 5 6 7 8 9 10 11 12breeding season non-breeding season

Breeding system: Monogamous.
Breeding season:
In Teurito Island, Hokkaido, the average egg-laying period varies
greatly between the years, ranging from the beginning of April tomid-May. They lay eggs earlier when the temperatures of air andwater are high in the early spring. They usually breed once a year,
but occasionally twice a year. They lay eggs 11.2 ± 5.3 days (N =206 nests) after they start to build a nest (Hayashi 1996).
They build a shallow nest with a diameter of about 60cm, using
mainly twigs and generally line the inner cup with seaweed anddried grass. The mean distance between the nests is about 1m.

Egg:
Japanese cormorant eggs are broadly
similar to a barrel in shape and mat bluish white in color. The eggs weigh 55.0
± 3.5g (49.6-59.7, N = 7) and are 63.0 ±2.1mm (59.5-66.2, N = 7) in length and39.7 ± 0.8mm (38.8-41.0, N = 7) in diameter (Watanuki et al. Unpubl.).
Roughly speaking, the eggs are about thesize of a smaller chicken egg. The clutch Photo 3. Nest and eggs ofJapanese Cormorants
size ranges from one to six eggs, mostly
three or four eggs with a mean of 3.28 ±0.79 eggs (N = 749 nests) (Kato et al. 2001).

Incubation and nestling periods and fledging rate:
The mean incubation period of JapaneseCormorants is 27.9 ± 2.1 days (N = 16nests) in Teurito Island (Hayashi 1996).
The male and female incubate the eggs
in shifts of two to several hours. The egg
mortality was attributed to the abandonment of incubation (117 eggs), hatchingfailure (102 eggs) and accidents including predation (76 eggs) (Hayashi 1996).
Photo 4. Japanese CorThe eggs hatch from early May to midmorant nestlings.
June in Teurito Island. The chicks areborn naked. The hatchlings ingest the food the parent birds haveregurgitated in the nest, but they eventually put their head into themouth of gaping parents to feed. Male and female take turns toleave the nest and forage in the sea for 2.2-5.7 hours during thenestling period (Kato et al. 2001). The meal mass (stomach content weight) amounts to 145 ± 20g (N = 23) (Watanuki et al.
2004). The growth rate of chicks is 92-99g per day (Kato et al.
2001) and the chicks leave the nest 50-60 days after hatching. Fora while after leaving the nest, the young occasionally come back to
the nest to be fed by parents (Hayashi 1996). On a hot day, theparents often carry the seawater in the gular pouch to the nest andspray it on the nestlings. The hatching and fledging rates are 37-95% and 46-84% respectively (Watanuki and Ito 2012). The death ofchicks resulted from nest abandonment (61 birds), starvation ordisease (49 birds), predation or accidents (11 birds) and disappearance (208 birds) (Hayashi 1996).

Diet and foraging behavior
Diet:
Photo 2. Breeding colonyof Japanese Cormorants.

♪ http://www.bird-research.jp/1_shiryo/koe/umiu_130619_muroran_kros.mp3
Reiko Kurosawa

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Nest:

Appearance:

Japanese Cormorants generally nest ina colony on relatively wide ledges ofcliffs, reefs and steep slopes of rocks.
They forage in coastal areas and often
rest on breakwaters of a harbor.

2Based on the study of the stomach contents regurgitated by theparents and nestlings captured in the breeding period or the foodBird Research News

Vol.7 No.6

2010.6.24.

© Japan Bird Research Association
Sumiyoshi 1-29-9, Fuchu, Tokyo, Japan
collected from the nestlings by neck-collar
method, the diet ofJapanese Cormorants
consists of sand lance,
naked sandlance, anchovy, sardine, atkamackerel, black rockfish, sculpin and flounder (Table 1). There isno information about
their food in the nonbreeding season.

バードリサーチ生態図鑑

Table 1. Diet of Japanese Cormorants
1992～1995
Weight ratio
sandlance fry
0～43 ％
sandlance adult (1 year old +) 0～67 ％naked sandlanceanchovy
0～61 ％
sardine0～24 ％
atka mackerel
0～77 ％
rockfish0～46 ％
sculpin0～29 ％
flatfish1～19 ％
gimpo classdacesquids
Study periods● Human use of Japanese Cormorants for traditional fishing

1996～1998
Frequency
5～29%
0～19%
0～32%
23～24%
3～29%
0～14%
14～24%
0～5%
0～6%
0～10%

Kato et al. 2001 Watanuki et al. 2004

Foraging behavior:
Japanese Cormorants chase ball-shaped dense shoal of schoolingsand lances that Rhinoceros Auklets chased up to the surface near
Teurito Island during the summer ("Here comes Darwin!" NHK2006). They tend to forage in a flock in the year when they primarily eat sand lance and anchovy (Watanuki et al. 2004). They usually forage at a depth of about 20 m around the island and off themain island, but sometimes forage in the area between the islandand the main island as well. Each bird has its own favorite feedingsite. The distance between the foraging and nesting sites is 7- 9 km
in males and 10-13 km in females. Each bird forages in an area of
83-170km2 in males and 199-200km2 in females (Ishikawa & Watanuki 2002). Japanese Cormorants are a generalist capturing both
epipelagic and demersal fish. In the year when the ocean temperature is low, they tend to eat sand lances in Teurito Island. In theyear when the temperature is high, on the other hand, they are out
in the sea for a longer time to forage for demersal fish that principally feed in the coastal area of the main island, which is a longway from their breeding grounds (Watanuki et al. 2004). If demersal fish represent a large proportion of the diet, the breeding performance (fledging rate) is decreased due to reduced feeding frequency resulting from extended foraging time (Kato et al. 2001).

Topics of ecology, behavior and conservation● Fish to capture and diving depth

010203040501.4Depth(m)Depth(m)Japanese Cormorants dive repeatedly to a depth of about 30m in
the year when they mainly forage for demersal fish, and 10 to 20m in the year when they primarily capture pelagic fish (Kato et al.
2001). The mean diving depth is 15.1 ± 3.7m (N = 6 birds) with amaximum of 45m for males and 7.2 ± 2.4m (N = 7 birds) with amaximum of 33m for females. Thus, males can dive deeper thanfemales. The mean diving period of males is 37 ± 5s with a maximum of 145s, while that of females is 24 ± 4s with a maximum of80s. Males can also dive longer than females (Watanuki et al.
1996).
The study of Japanese Cormorants using a depth logger and a radio transmitter suggested that they foraged close to the bottom of
the sea at a depth of more than 20m around Teuri Island and in thecoastal area of the main island which was less than 40m in depth.
On the other hand, they foraged for pelagic fish at a depth of about
10 m in areas more than 40m in depth (Kato et al. 1998).

1.6Time(hr)1.801020304050
0.4

0.6Time(hr)Fig. 1. Comparison of Japanese Cormorant diving behavior in a shallow
area (left) and a deep area (right)

0.8Fishing using cormorants is a special method handed down sincethe 7th century approximately in China and Japan. Chinese people
use Great Cormorants for fishing without keeping them on a rope
because Japanese Cormorants do not occur in China. Japanesepeople use Great Cormorants and Japanese Cormorants, both ofwhich are found in Japan, but they mostly use Japanese Cormorants on a rope because Japanese Cormorants are larger and more
physically fit for diving, gentler in nature and they have a thicker
throat to hold a greater amount of fish (Juou-cho 2000). "FuneUkai (cormorant fishing on a boat)" of Inuyama, Gifu and Kyoto iswell known, but there is also another type of cormorant fishing inwhich fishermen enter a river and manipulate cormorants, which iscalled "Kachi-U". Juvenile Japanese Cormorants are captured onthe coast of Juo Town, Hitachi City, central Japan during thespring and autumn migration seasons and large birds more than 2.5
kg in weight are selectively used for fishing across the country.

Literature
Hasegawa H. 1984. Status and conservation of seabirds in Japan, with special
attention to the short-tailed albatross. In: Croxall, J.P., Evans, P.G.H. &Schreiber, R.W. (eds), Status and Conservation of the World's Seabirds, ICBPSpecial Publ No1, pp 487-500.
Hayashi E. 1996.Factors that affect the reproductive performance and breeding
ecology of Japanese cormorant (Phalacrocorax capillatus). Thesis for MS,
Graduate School of Agrictulture, Hokkaido University). [J+E]
Ishikawa K. & Watanuki Y. 2002. Sex and individual differences in foraging behavior of Japanese cormorants in years of different prey availability. J. Ethol.
20: 49-54.
Juou-cho. 2000. Coexistence with Japanese Cormorants.Ju-o Town one village one
cultural creation business promotion committee. [J]Kato A., Watanuki Y. & Naito Y. 1998. Benthic and pelagic foraging of two Japanese Cormorants, determined by simultaneous recording of location and diving
activity. J Yamashina Inst Ornithol 30:101-108.
Kato A., Watanuki Y. & Naito Y. 2001. Foraging and breeding performance ofJapanese Cormorants in relation to prey. Ecol. Res. 16: 745-758.
NHK Darwin has come! . 2006. Darwin video!Rhinoceros Auklet "feather". http://www.nhk.or.jp/darwin/darwinmov/index.html
Osa Y. & Watanuki Y. 2002. Status of seabirds breeding in Hokkaido. J. Yamashina Inst. Ornithol. 33: 107-141.
Siegel-Causey D. & Litivinenko N.M. 1993. Status, ecology, and conservation ofshags and cormorants of the temperate North Pacific. In: Vermeer, K., Briggs,K.T., Morgan, K.H. & Siegel-Causey, D. (eds), The Status, Ecology, and Conservation of Marine Birds of the North Pacific, Can Wildl Spec Publ, pp122130.
Takano S. 1982. Field guide of Birds of Japan. Wild Bird Society of Japan. [J]Watanuki Y., Ishikawa K., Takahashi A. & Kato A. 2004. Foraging behavior of ageneralist marine top predator, Japanese Cormorants, in years of demersal vs.
epipelagic prey. Marine Biology 145: 427-434.
Watanuki Y. & Ito M. 2012. Climate effects on breeding seabirds of the Northern
Japan Sea. Mar Ecol Prog Ser 454:183-196.
Languages of literature cited other than English: [J] in Japanese, [J+E] in Japanesewith English summary.

AuthorYutaka WATANUKI Hokkaido University Fisheries Sciences Research Institute
I was born in Nagano in 1959 and received my doctorate in Agriculture at Hokkaido University in 1987. A research assistant at the National Institute of Polar Studies between 1988 and 1993. I studied Adelie Penguins at Showa Base in Antarctica. After working in the Graduate
School of Agriculture of Hokkaido
University, currently an Associate
Professor of Fisheries Sciences Research Institute of Hokkaido University. Field of study: behavioral ecologyof animals and marine ecology.
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