 Pelicans frequent inland and coastal waters where they feed principally on fish , catching them at or near the water surface . They are gregarious birds , travelling in flocks , hunting cooperatively and breeding colonially . Four white @-@ plumaged species tend to nest on the ground , and four brown or grey @-@ plumaged species nest mainly in trees . The relationship between pelicans and people has often been contentious . The birds have been persecuted because of their perceived competition with commercial and recreational fishing . Their populations have fallen through habitat destruction , disturbance and environmental pollution , and three species are of conservation concern . They also have a long history of cultural significance in mythology , and in Christian and heraldic iconography . 
