California Department of Fish and Wildlife

Bay Delta Region

Biological Resources

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

Stockton Office
  2109 Arch Airport Rd
  Stockton, CA 95206
  (209) 234-3420

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

Great Blue Heron

Ardea herodias
California Department of Fish and Game "Special Animal"

Life History

This is a lean, grayish-blue heron. The body of the great blue heron averages 46 inches in length and has a wingspan of 72 inches. This bird is easily recognizable by it size, color, the black stripe that extends above the eye, and a white foreneck that is streaked with black. Breeding adults have ornate plumes on their head, neck, and back. In flight, the folded neck as well as slow, long wingbeats is a strong indicator that the bird is a heron.

This heron is monogamous and usually nests in colonies in the tops of secluded large snags or live trees, picking the tallest available. Courtship and nest building begin shortly after February and the eggs are laid in late February or March. Clutch size can be one to eight eggs, but averages three or four. The incubation of these eggs takes about 28 days at which time the hatched young are cared for by both adults. The young may fly by seven weeks but still return to the nest for two to three weeks after that and may continue to be fed by the adults for another week or so.

Tall riparian-type trees are needed for perching and roost sites. Also, secluded large snags or groves of live trees are needed for colony nesting. These need to be located within ten miles of feeding areas.

This bird is fairly common in shallow estuary systems and fresh and saline emergent wetlands all year throughout most of California. They are somewhat less common along riverine systems, rocky coastlines, croplands, pastures, and in the mountains above the foothills.

The slender bill of the great blue heron, 4-1/2 to 6 inches long, serves as an effective pincher for its food items. Nearly 75 percent of the diet is fish, mostly species not sought by humans (Cogswell 1977), but they will also prey on small rodents, amphibians, reptiles, insects, crustaceans, and occasionally small birds. Feeding behavior includes standing motionless in one place, probing, pecking, or walking slowly when searching for prey in shallow water. Diving for fish in deeper water has been observed occasionally but is considered to be unusual behavior for this species (Bent 1963, Dickinson 1947, Gordin 1977).

Findings and Conclusion

The great blue heron is designated a "Special Animal" because of the close association it has with a habitat that is continuing to decline in California. Additionally, tree cutting, water recreation, draining of wetland habitats, building, and highway construction have all contributed to rookery abandonment in recent years.

Great blue herons were observed in small numbers by CDFG biologists along the Stanislaus River. Caswell State Memorial Park reports a historical rookery within park boundaries. Any project affecting flows of the river could impact foraging areas and the riparian corridor. Further surveys for great blue heron rookeries would be recommended prior to any project.