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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
Western Grebe
Aechmophorous occidentalis
California Department of Fish and Game "Special Animal"
Life History
The western grebe is a black and white bird measuring about 25 inches in length with a
long, swan-like neck and long, thin bill. The black coloration extends from the forehead,
along the back of the neck, and over the entire back. In the dark phase, this black cap
includes the eyes and the bill is yellow-green in color; the light phase does not have such an
extensive black cap and the bill is yellowish-orange in color. The dark phase is the
predominate color in the north and east while the light phase is predominate in the south.
Calls of the two phases are distinctive of one another. The dark phase has a two-note courting
call while the light phase has a longer single note.
Courtship occurs from April to May and nests are occupied from May to August.
Courtship consists of dramatic displays that involve sprinting across the water with their
necks' kinked. These gregarious birds require large, open water areas for courtship, feeding,
and flocking, and frequent extensive beds of tall, emergent vegetation such as tules or cattails
for nesting. These monogamous, colonial nesters construct a nest platform that is built up from
the bottom and floats in water up to ten feet deep. The nest is usually constructed near open
water. The clutch size is usually three to four eggs and replacement clutches are not
uncommon. They are single brooders but both parents care for the precocial young.
Incubation is about 23 days long. Upon hatching, they are tended to for about four to five
weeks at which time they are almost full grown.
All food is obtained by diving and pursuing prey at depths of at least four feet but it is
not uncommon for them to use shallower water during the summer months. The diet consists
primarily of fish but also includes insects and other invertebrates, but rarely includes
amphibians and plants. As with other grebes, feathers are eaten by adults and young and
accumulate in the stomach.
Findings and Conclusions
The destruction of wetlands and the introduction of pesticides into watersheds are major
causes of a continuing decline in numbers (Feerer and Garrett 1977). Other human
disturbances such as lakeshore development near nesting colonies and disturbance by boaters
and fisherman are also detrimental (Gould 1974, Lederer 1976).
Any project affecting flows of the Stanislaus River or the
wetlands associated with the river could have adverse affects on the western grebe and would
warrant further studies.
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