The Gull-billed Tern - Sterna nilotica - at a distance looks like a seagull; it is nearly white overall, except for the short, thick, black bill, black legs, in breeding birds a black cap extends down to the bill, including the eye and extending onto the nape. Eye is dark. Upperparts of body are whitish-grey; underparts white. Upper wings, back and tail are silvery white; outer wings darker grey. Males and females similar, 37 to 45 cm long.
In non-breeding birds the black cap is replaced by a black streak on white background with a black streak through the eye. Immature birds are coloured as non-breeding adults with mottled brown on the shoulders.
Gull-billed Terns are birds of surface waters on land ranging over coastal swamps and inlets over much of the Australian inland on flood sheets and inlets; uses fresh or brackish water but rarely visits marine environments. Everywhere nomadic and migratory. More usually seen in ones and twos at any time of the year when not breeding.
Terns patrol over open waters and mud flats at heights of 5 to 30 metres, or skim low over flooded saltbush plains; never far from the shore. When prey is seen the bird turns and glides down with tail fanned and bill tilted down, to seize the food item from the surface. Inland they eat fish, crustaceans and insects; on coastal swamps they eat fish and crabs.
Nesting takes place from September to May; birds gather in colonies containing tens to hundred of birds to nest, mostly on remote inland lagoons after rain or flooding. Nests are a bare depression on the ground or a platform of dry plant matter on bushes in samphire. Nests may be 40 centimetres or four metres apart. Two to four eggs are laid; glossy yellow-grey to olive, blotched dark grey and dusky brown; ellipse shaped, about 50 by 37 millimetres. Incubated by both parents for 22 to 23 days.
¶ Genus Sterna is in Family Laridae containing the Gulls, Terns and Noddies. This genus contains the typical terns in the family.