Interior Least Tern

The interior least tern is the smallest tern.  It is a swallow-like bird eight to nine inches long with a wing span of 20 inches. It is also called the sea swallow for its delicate, graceful and buoyant flight. Distinguishing marks of the least tern include its glossy black crown, white forehead and undersurface, pale gray back and wings, and the black-tipped yellow-orange bill. The short legs and webbed feet are orange (males) or pale yellow (females). The long, black outermost wing feathers and the short, deeply forked tail are conspicuous in flight. Immature birds have a dark bill, a dark gray eye stripe, a white forehead and a dusky brown cap.  Wintering birds are paler than breeding birds and they have brownish-black bills, a dark gray eye stripe and white and black feathers on the head.  Interior least terns eat small fish captured in the shallow water of rivers and lakes. They hunt by hovering, searching and then diving from a few feet to 30 feet above the surface to snatch small fish into their bills.

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.  The interior least tern has distinct breeding and wintering areas. Most breeding occurs on interior rivers. The interior least tern breeds locally along the major tributaries of the Mississippi River drainage basin from eastern Montana south to Texas and east to Illinois, Missouri, Arkansas and Louisiana.  The occurrence of breeding least terns is localized and is highly dependent on the presence of dry, exposed sandbars and favorable river flows that support a forage fish supply and isolate the sandbars from the riverbanks.  Nesting sites are usually dry, flat, sparsely vegetated sand- and gravel bars within a wide, unobstructed, water-filled river channel. Interior least terns breed in isolated areas along the Missouri, Mississippi, Ohio, Red, and Rio Grande river systems.