the ring-billed gull (larus delawarensis) is a medium-sized gull .
the genus name is from latin larus which appears to have referred to a gull or other large seabird .
adults are {convert|49|cm|in|abbr=on} length and with a {convert|124|cm|in|abbr=on} wingspan .
the head , neck and underparts are white; the relatively short bill is yellow with a dark ring; the back and wings are silver gray; and the legs are yellow .
the eyes are yellow with red rims .
this gull takes three years to reach its breeding plumage; its appearance changes with each fall moult .
their breeding habitat is near lakes , rivers or the coast in canada and the northern united states .
they nest colonially on the ground , often on islands .
this bird tends to be faithful to its nesting site , if not its mate , from year to year .
the ring-billed gull is a familiar sight in the shopping mall parking lots of the united states , where it can regularly be found congregating in large numbers .
in some areas , it is displacing less aggressive birds such as the common tern .
they are migratory and most move south to the gulf of mexico and the atlantic and pacific coasts of north america , also the great lakes .
this gull is a regular wanderer to western europe .
in ireland and great britain it is no longer classed as a rarity , with several birds regularly wintering in these countries .
these birds forage in flight or pick up objects while swimming , walking or wading .
they also steal food from other birds and frequently scavenge .
they are omnivorous; their diet may include insects , fish , grain , eggs , earthworms and rodents .
these birds are opportunistic and have adapted well to taking food discarded or even left unattended by people .
it is regarded as a pest by many beach-goers because of its willingness to steal unguarded food on highly crowded beaches .
the gull's  natural enemies are rats , foxes , cats , raccoons , coyotes , hawks , eagles , and dogs .
