The land birds of Costa Rica are the bestknown of Central America, thanks to the efforts of Slud (1964) and several later authors. However, over the years the waterbirds have been relatively neglected. Save for the accounts of selected species by Orians and Paulson (1969), little recent information is available on the rich freshwater avifauna of northwestern Costa Rica. The only careful account of seabirds in Costa Rican waters