Least terns are among the smallest of the terns, measuring 8 to 9 inches in length. Both sexes have a black cap and nape, white forehead, grayish back and wings, white belly, orange legs, and a black-tipped yellow bill.
Immature birds have darker plumage, a dark bill, dark eye stripes, and white heads.
This high-flying aerial display with one or two other terns is done while carrying a fish in his bill that the female takes and eats. Female terns usually lay one to four eggs around late May to early August in colonies of about 20 small ground nests. Preferred river systems for the interior least tern are those with bare or nearly bare alluvial islands or sandbars, favorable water levels during the nesting season, and food availability. Historically, interior Least terns bred along the Colorado, Red, Rio Grande, Arkansas, Missouri, Ohio, and Mississippi Rivers. Current studies indicate that this tern is extremely limited in both numbers and distribution.