How many seabirds were killed by the Exxon Valdez Oil Spill?

After the Exxon Valdez oil spill of 24 March 1989, 36,115 dead seabirds were recovered from beaches and processed at morgues. Most or all of 1,888 live oiled seabirds brought to rehabilitation centers also died and about 3,260 oiled carcasses were never delivered to morgues. Of these 41,263 carcasses accounted for, we estimated conservatively that only 30,000 were killed by oil pollution. Carcass drift and recovery experiments conducted in the affected area during the spill and 1 year later, along with historical experiments conducted in other oceanographic regions, suggest that only a fraction (range = 4-30%) of birds killed were likely to have been recovered from beaches. Regression analysis of these drift-recovery data predicts a 15% recovery rate (r' = 0.38, P = 0.015). We recognize uncertainties in the assumptions and parameter values used to extrapolate total mortality from drift-recovery data, but we have confidence that mortality fell within the extreme range of estimates (100,000-690,000 birds killed) because these reflect a very wide range of observed and experimentally determined parameter values. Total mortality can also be estimated by comparing pre- and postspill colony population estimates. Uncertainties about these census data are greater than those associated with drift-recovery data, but nonetheless provide an independent mortality estimate of similar magnitude. Taken together, all evidence suggests that about 250,000 seabirds were killed by Exxon Valdez oil.