On 27 April 1988 we visited the coastal lagoons at La Ventosa, 5 km east of Salina Cruz, Oaxaca, Mexico. Scanning through a flock of about 800 Laughing Gulls (Larus atricilla) and 200 Franklin’s Gulls (L. pipixcan) we were surprised to see two adult Yellow-footed Gulls (L. livens). While we were watching these, a third large dark-backed gull flew over us and landed in the flock. As it appeared smaller, slighter, and paler-backed than the Yellow-footeds, the possibility of a Lesser Black-backed Gull (L. fuscus) crossed our minds. Closer examination, however, showed this bird to be a Western Gull (L. occidentalis). We approached the gulls to within 50 m and watched them at rest and in flight over the course of three hours. The following descriptions are taken from our field notes.