These gregarious birds are usually seen in flocks or small groups (3). They feed on worms, other soil invertebrates, scraps, rubbish, carrion and fish (3) (5). During winter, black-headed gulls roost on open water, typically fresh water, although they may occasionally make use of sheltered estuaries (5).

These gulls nest in colonies, within which pairs defend small territories. They will defend these territories from other birds using ritualised displays (7). Two to three eggs are produced which are incubated for up to 26 days. After a further 35 days the chicks will have fledged (3). Black-headed gulls are fairly long lived, with a maximum recorded life-span of 32 years (3).