<P> The general pattern of plumage in adult gulls is a white body with a darker mantle; the extent to which the mantle is darker varies from pale grey to black . A few species vary in this, the ivory gull is entirely white, and some like the lava gull and Heermann's gull have partly or entirely grey bodies . The wingtips of most species are black, which improves their resistance to wear and tear, usually with a diagnostic pattern of white markings . The head of a gull may be covered by a dark hood or be entirely white . The plumage of the head varies by breeding season; in nonbreeding dark - hooded gulls, the hood is lost, sometimes leaving a single spot behind the eye, and in white - headed gulls, nonbreeding heads may have streaking . </P> <P> The gulls have a worldwide cosmopolitan distribution . They breed on every continent, including the margins of Antarctica, and are found in the high Arctic, as well . They are less common on tropical islands, although a few species do live on islands such as the Galapagos and New Caledonia . Many species breed in coastal colonies, with a preference for islands, and one species, the grey gull, breeds in the interior of dry deserts far from water . Considerable variety exists in the family and species may breed and feed in marine, freshwater, or terrestrial habitats . </P> <P> Most gull species are migratory, with birds moving to warmer habitats during the winter, but the extent to which they migrate varies by species . Some migrate long distances, like Franklin's gull, which migrates from Canada to wintering grounds in the south of South America . Other species move much shorter distances and may simply disperse along the coasts near their breeding sites . </P> <P> Charadriiform birds drink salt water, as well as fresh water, as they possess exocrine glands located in supraorbital grooves of the skull by which salt can be excreted through the nostrils to assist the kidneys in maintaining electrolyte balance . </P>

Where do canadian seagulls go in the winter