It was once called sea swallow for its delicate, graceful and buoyant flight. The short legs and webbed feet of the male are orange, those of the female pale yellow. The long, black outermost wing feathers and the short, deeply forked tail are conspicuous in flight. The plumage of immature terns is darker gray than the adults. Immature birds have a dark bill, a dark gray eye stripe, a white forehead and a dusky brown cap.
Young birds acquire adult plumage characteristics during their second year.
Wintering birds are paler than breeding birds and are identifiable by their brownish-black bill, dark gray eye stripe and white and black feathers on the head. The orange legs and feet become a pale yellow. Habits Interior least terns usually arrive on their breeding grounds in early to mid-May and begin to establish feeding and nesting territories. During the breeding season, the terns home range is generally limited to a two-mile stretch of river associated with the nesting colony. Least terns nesting at sandpits along rivers use the adjoining river as well as the sandpit lake itself for foraging.