A large colony of herons, egrets, and cormorants is present in the south arm of North Stone Lake in the Stone Lakes National Wildlife Refuge, just south of Sacramento near the I5 Freeway. This colony supports approximately 268 nests and has been identified as the most inland nesting colony of cormorants on the Pacific coast.

In May 1994, during a routine survey of nesting colonial waterbirds, a cormorant nestling with a deformed bill (no lower mandible) was observed at North Stone Lake.

To investigate possible causes of this deformity, we analyzed trace metals, organochlorine pesticides (OCs), and polychlorinated biphenyls (PCBs,) in samples of water, sediment, fillets and whole body fish, and bird eggs collected from water bodies around the Stone Lakes National Wildlife Refuge.

Copper and lead concentrations were elevated in water samples from certain sites. There were numerous criteria exceedences for trace metals in sediment samples. Arsenic, cadmium, chromium, copper, lead, nickel, and zinc were elevated at two or more sites.

Concentrations of lead and nickel from some sites exceeded Probable Effects Levels. OC and PCB concentrations were low in sediment and wildlife samples. Trace element concentrations were also low in wildlife samples.

Further monitoring of trace metals and storm events was recommended for the north end of the refuge which receives drainage from the rapidly growing urban areas of south Sacramento County.  

Double-crested cormorant nesting at Stone Lakes National Wildlife Refuge