Stanislaus River Basin and Calaveras River Water Use Program
Threatened and Endangered Species Report - March 1995
Bay Delta and Special Water Projects Division, CA Dept of Fish and Game
Great Egret
Casmerodius albus
California Department of Fish and Game "Special Animal"
Life History
The great egret is 39 inches long with a 51 inch wing span (National Geographic 1983).
The most noticeable physical characteristics are its white body feathers, black legs and feet,
large yellow bill, and during the breeding season the long plumes on the back and tail.
Immature birds normally have dull black or brown legs and lack the elegant plumes. The
snowy egret is distinguished by its smaller size, black bill, and yellow feet, and an occasional
crest on the head. This crest is usually present only during the breeding season.
Great egrets are usually seen feeding in mud or shallow water and along shores of
estuaries, lakes, ditches, slow moving streams, salt ponds, mud flats, and in irrigated
croplands and pastures (Granholm 1988). Egrets walk slowly in a forward leaning position,
stalking lizards, snakes, frogs, tadpoles, insects, fish, snails, and small rodents. They
congregate on newly flooded pastures or where cattle are present.
Egrets often feed separately but usually return to roost at night in trees with other egrets.
In early spring they pair up for breeding and nests of sticks, stems, and marsh plants are built
in large trees near water. Nests in the rookery are built between ten and 80 feet off the ground
(Granholm 1988) and are often sheltered from prevailing winds (Yull 1972, Ives 1973). A
single clutch of three to five eggs is laid between March and July. Incubation lasts 26 days
after which downy, semi-altricial young are born. Age at first flight is probably five to six
weeks, but there is no information on ages at independence or age at first breeding (Palmer
1962).
Findings and Conclusions
The category "Special Animal", in the case of this bird, is because the bird is closely
associated with a habitat that is declining in California. Although plume hunters greatly
reduced populations near the turn of the century (National Geographic 1983) and recent water
developments have further negatively influenced population densities, of most concern is their
nesting environment. Human disturbances negatively affect clutch success and even more
importantly thinning of trees at riparian nest sites reduces protection against high winds and
avian predators. Identification and protection of egret rookeries is needed to protect this bird.
Egrets breed locally in California, southeast Oregon, Nevada, northern Utah, Colorado,
west Arizona, New Mexico, and west Texas (Peterson 1961). The range of breeding egrets
may go as far north as Canada. The northwest coast and Central Valley of California are
home to many year around individuals. Great egrets have been observed feeding in and along
the Stanislaus River by CDFG biologists and even though no rookeries have been identified it
offers thick riparian stands of large trees and abundant food sources.
Any project proposed for the Stanislaus River should consider the impacts to both feeding
resources and potential nesting habitat.
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