We investigated attributes of 5 colony sites of endangered least terns (Sterna antillarum athalassos) nesting on the Arkansas River from Tulsa to Muskogee, Oklahoma, in 1992 and 1993. We tested hypotheses that least terns selected areas to nest with the lowest amount and height of vegetation and nested near driftwood or similar debris. River flows prior to the nesting season in May 1993 scoured all sandbars, removing vegetation and increasing abundance of driftwood. Attributes of colony sites of nesting least terns varied substantially from one location to another. Distances from nests and random points to vegetation and driftwood varied among colony sites. Occurrence of driftwood at colony sites increased after floods in 1993, and least tern nests at 4 of 5 colony sites were significantly closer to driftwood than were random points inside a colony. Nests at all colony sites surveyed were situated on sandbars at maximal distances to the narrowest water barrier from shores of sandbars to the river bank. Our results suggest that river flows that elevate sandbars before the nesting season ultimately will enhance recovery of endangered least terns on the Arkansas River by reducing losses of nests to flooding, retarding establishment of vegetation, and increasing abundance of driftwood.
