California Department of Fish and Wildlife

Bay Delta Region

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  7329 Silverado Trail
  Napa, CA 94558
  (707) 944-5500

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  Stockton, CA 95206
  (209) 234-3420

Acting Regional Manager:
Scott Wilson

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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

Osprey

Pandion haliaetus
California Department of Fish and Game "Species of Special Concern" and a U.S. Forest Service Sensitive Species

Life History

The osprey is sometimes known as the "fish hawk". It is a large, long-winged raptor that has a white body and a dark line through its eye. The osprey measures 21 to 24.5 inches in length and has a wingspread of 4-1/2 to 6 feet. In flight, the wings are held with a gull-like crook and have slow and deep wing beats.

It appears that ospreys mate for life. Between April and June, three eggs are laid with the female incubating them for approximately 28 days. Even when the young leave the nest they continue to associate with their parents.

Ospreys are considered rare winter transient visitors to the Central Valley but are fairly common in the foothills of the northern Sierra Nevada mountains and coastal ranges. Almost the entire North American population winters in the Caribbean, Central America, and the northern area of South America. The exception is a few birds remaining along the Gulf Coast and in the southern parts of California.

The osprey feeds almost entirely on fish, but will also feed on a few mammals, birds, amphibians, and invertebrates. Some of the fish species recorded in the diet of the ospreys are herring, carp, catfish, eel, flounder, goldfish, perch, salmon, shad, trout, and sunfish. The osprey is not a deep diver and catches only those fish that swim on or near the water's surface or in shallow water.

Findings and Conclusions

CDFG biologists observed an individual flying overhead along the Stanislaus River in the valley reach in November 1994. In addition, ospreys have been cited by others along the Stanislaus River, primarily in the fall and winter (Reeve pers. comm.). The closest reported nesting attempt was along the Tuolumne River near the town of LaGrange in 1991 (Reeve pers. comm.). This unsuccessful nest location is less than 10 miles south of the Stanislaus River and it should be noted that suitable habitat does occur along the Stanislaus River, especially in the foothill and canyon reaches.

Any project affecting flows of the Stanislaus River could impact this species necessitating further surveys to determine usage.