Whilst not overpoweringly large, Heermann’s gull frequently harasses other seabirds into relinquishing their catch, picking mainly on the brown pelican (Pelecanus occidentalis) and the California sea lion (Zalophus californianus). It takes small fish from the water surface and sometimes dives to chase fish. It also scavenges and feeds opportunistically on lizards, insects, invertebrates and herring gull eggs along beaches, estuaries and marshes (2) (3).
Heermann’s gull prefers to forage alone or in small groups, but during the breeding season it forms large colonies on the ground. Up to 100 pairs construct nests out of twigs and stones between rocks, lining the nest with feathers or shells. The female lays one to three spotted eggs in late April, which are incubated by both parents for 28 days. They hatch between mid and late May and the hatchlings are fed by the male and the female until they fledge 45 days later. If food is scarce, parents may choose one chick to feed, starving the other or even pecking it to death. Chicks that survive until adulthood begin to breed at three or four years of age (2) (3).