Small numbers winter locally, mainly in southern California. A monogamous, colonial nester, in groups of a few to several hundred pairs. Clutch size is usually 2 eggs, sometimes 1, with up to 6 reported. Altricial young are fed by both parents, and leave the nest at 3-4 wk. The major natural enemies are gulls, which steal eggs, but only in small numbers.
Coyotes can eliminate colonies if islands become connected to shore.
Susceptible to pollution of watershed by persistent pesticides. Degradation of breeding habitat has eliminated several major colonies in California. Serv., Lassen Natl. For., Susanville. 590pp. Cogswell, H. L. 1977.