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Stanislaus River Report
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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
Double-crested CormorantPhalacrocorax autirus
California Department of Fish and Game "Species of Special Concern"
Life HistoryThe double-crested cormorant is a year round resident to the Central Valley. This large (32 inches long) bird is dark in color with an orange throat patch. The immature birds are dark brown but tend to have lighter chest and throat patches. During breeding season the adults have two tufts that extend behind the eye and are usually white in color.
The diet of the double-crested cormorant consists primarily of fish, but also contains crustaceans and amphibians. Food items are captured under the surface of the water with the cormorants remaining under water for up to 30 seconds. Cormorants prefer to fish and feed in water that is less than 30 feet deep and that has rocky or gravel bottoms, but they have been noted to dive as deep as 70 feet.
Breeding occurs mostly from April to August for these monogamous birds. Nests can be found on wide rock ledges on cliffs, rugged slopes, and live or dead tall trees. Eggs are reared in colonies of a few to thousands of pairs of cormorants. Territories exist for courtship and nesting and consist of a perch for the non-incubating bird. The clutch size is usually from three to four eggs and are incubated for 24 to 30 days. The young are born altricial and fly after about five to six weeks, becoming totally independent at about 10 weeks.
Findings and ConclusionsThe cormorant is very susceptible to disturbance during the nesting season and success in the colony is dependent on disturbance-free zones. Human disturbance and habitat destruction has caused nest abandonment while increased predation by gulls and crows may have an influence in reducing nesting success.
Double-crested cormorants were observed by CDFG biologists in all three reaches of the river. Although they are not believed to nest along the Stanislaus River, any project which would impact flows could affect this species.