Wednesday, Nov. 26, 2008 Japan Times
By ROWAN HOOPER
Pacific reef egret
* Japanese name: Kurosagi
* Scientific name: Egretta sacra
* Description: As egrets in Japan go, reef egrets are medium-size, growing to around 65 cm in length, with a wingspan of up to 110 cm. They weigh about 400 grams. As for their color, that’s not straightforward: Some are pure white, while others (such as the one in the photo) are charcoal-gray. The reasons for the existence of different-colored “morphs” are unknown. They have short legs, yellow in the white morph and gray in the gray morph; brown beaks; and gold-yellow eyes. In the gray morph, there is a narrow white stripe on the throat.
* Where to find them: From Honshu to Kyushu and Okinawa, along the coasts and on islands. The dark form predominates in more temperate areas, but moving south the white form is more common.
* Food: Small marine fish, crustaceans, mollusks and insects. Reef egrets are active foragers day and night, and sometimes they invade the colonies of other seabirds, such as terns and gulls, and steal fish the other birds have caught for their young. Reef egrets have a distinctive feeding style, stalking over rocks and in shallow water, bent low.
* Special features: There are various theories as to why reef egrets exist in two color morphs. It could be related to the particular local climate (dark forms being better suited to colder areas), or it could be a camouflage tactic whereby different colors have feeding advantages according to the local prey abundance. Reef Egrets breed year-round, constructing a nest platform lined with seaweed, and can form small colonies with other egrets. Whenever birds nest together, there is the potential for conflict — if a female sneaks off to copulate with a male other than her mate, or if male birds mate with other females, or simply if birds steal each other’s food. This could be the reason for reports of extreme aggression — even killing — between adult reef egrets. Males and females share the job of raising the young, which requires 28 days of brooding the eggs and five weeks of feeding the chicks.
PHOTO COURTESY OF BIO-IMAGE NET