This species can be found on coasts, lakes, marshes, field and rubbish dumps. It feeds almost exclusively on earthworms or emerging chironomids, but also aquatic invertebrates, grasshoppers and incidental small rodents and small fish. Early arrivals to colonies may depend on grain or sunflower seeds before insects become available. In winter small fish make up an important part of the diet, as do fish offal and refuse. Breeding is highly synchronous, with individuals arriving at colonies in mid-April and laying in mid- to late May. It is a highly gregarious species, forming colonies from 100's to over 10'000 pairs at inland lands and marshes, with nesting requiring emergent vegetation (del Hoyo et al. 1996).

This species breeds in the northern USA and central-west Canada, migrates south through Central America and winters off the west coast southern Mexico, Central America and of South America, where it is particularly common from Ecuador to Chile (del Hoyo et al. 1996).