Mostly white below and light gray above; black bill, legs, and feet. Breeding plumage: Black crown and nape. Winter plumage: Top of head, back , wings, and tail gray; under parts white. 6 cm (14 in) in length; 86 cm (34 in) wingspan. Large thick bill and a deeply notched tail.
The breeding season usually begins in early May and extends to early August. The Gull-billed Tern nests in colonies, commonly with large numbers of nests in an area. It often nests with Common Terns and Black Skimmers. Breeding habitat includes sand, gravel, or shell beaches, or some grassy areas of coastal islands. The nest is usually built in a depression on the ground. Both the male and female line the depression with grass and other vegetation. The female lays 1-4 (usually 2-3) eggs that both adults incubate for 22-23 days. The young are semi-precocial and leave the nest a few days after hatching. The young are dependent upon the adults for 28-35 days after hatching.
The habitat this species uses during the non-breeding season is similar to its breeding season habitat. Its diet includes insects, small mammals, frogs, crustaceans, and sometimes bird eggs, bird young, and fish. Unlike many of the other terns, the Gull-billed Tern forages mostly over land, sitting on a perch and flying out to catch insects in mid-air. This species is migratory.
During the breeding season, the Gull-billed Tern occurs in the eastern and southern coastal United States. It is also seen during the winter along the southern coastal United States. Its winter range extends to central coastal areas of South America.
This species is not common, but is not yet listed as Threatened or Endangered in any part of its southeastern range. The numbers of Gull-billed Terns are declining. The original massive decline in numbers was caused by hunters gathering plumes for the fashion industry of the late 1800s and early 1900s, during which time these birds were eliminated from the northern portion of their breeding range.
Some other terns are very similar to the Gull-billed Tern. The black legs and feet and the thick bill of this tern differentiates it from species such as the Forester's Tern and the Least Tern.