In southern California, most numerous at the Channel Islands and at San Diego Bay, where a few nonbreeders remain through the summer. While breeding, confined to the shores of North and Central America, and equatorial West Africa. Usually nests on sandy beaches or dredging spoils.
Ideal locations are at, or near, inlets between bays and oceans.
Often nests near other species such as gulls, terns, or skimmers. Yearlong, diurnal activity. This species roosts much of the day on beaches, dikes, estuaries, or lagoons. Perhaps as an antipredator device, nests exceptionally close together. Young are semiprecocial, and leave the nest permanently after about 15 days.