Demographics of Aechmophorus Grebes Killed in Three Mortality Events in California

Oil spills in coastal California are a conservation concern for many seabird species and are among the top threats to wintering populations of Aechmophorus grebes. Western Grebes A. occidentalis and Clark’s Grebes A. clarkii are sister taxa that breed in freshwater lakes throughout western North America and predominantly spend the nonbreeding season in the nearshore marine environment, where they are vulnerable to oiling (Storer & Nuechterlein 1992). In California, Western Grebes are one of the main species impacted by oil spills (California Department of Fish and Game [CDFG] 1969a,b; Straughan 1970, 1971; American Trader Trustee Council 2001; Hampton et al. 2003; Carter 2003; CDFG et al. 2004; CDFG & US Fish and Wildlife Service [USFWS] 2008; Humple 2009; Oiled Wildlife Care Network [OWCN] / PRBO Conservation Science unpubl. data). Understanding demographic parameters — such as sex and age ratios — of impacted populations is critical to assessing immediate and potential long-term effects of oil DEMOGRAPHICS OF AECHMOPHORUS GREBES KILLED IN THREE MORTALITY EVENTS IN CALIFORNIA