The primary breeding colonies of Heermann’s Gull (Larus heermanni) are on islands in the Gulf of California, Mexico. Only two colonies are known from the Pacific side of the Baja California peninsula. One was on Isla San Roque (27°09’N; Grinnell 1928), where Huey (1927) found 35 pairs beginning to lay on 20 April 1927. The second colony, previously the northwesternmost for the species, was discovered on Isla Benito del Centro of the San Benito Islands (28°20’N) on 25 May 1971, when Jehl (1976) found 25 adults and nine nests containing one to five eggs each. Later surveys disclosed 15 adults and two active nests with one small chick each on 21 June 1974 (Jehl 1976) and at least 30 adults, eight scrapes and eight nests containing eggs and/or small chicks on 9 June 1975 (Boswall 1978).
In this paper we describe the first nesting attempts by Heermann’s Gull in the United States. The species nested at two locations in California: on Alcatraz Island in 1979, 1980 and 1981, and at Shell Beach in 1980. Brief accounts were published by Binford (1980) and by Laymon and Shuford (1980) for Alcatraz and by Sowls et al. (1980) for Shell Beach.