Interior Least Tern Sandbar Nesting Habitat Measurements from Landsat TM Imagery-Data

Sandbars of large sand-bedded rivers of the Central U.S. serve important ecological functions to many species, including the endangered Interior Least Tern (Sternula antillarum) (ILT). ILT are colonial birds which feed on fish and nest primarily on riverine sandbars during their annual breeding season of approximately May through July, depending on region. During this time, ILT require bare sand of sufficient elevation so as not to be inundated during the period between nest initiation and fledging of hatchlings. ILT were originally listed as endangered due in part to decreases in available sandbar habitat from river channelization and impoundment. Sandbars in Central U.S. rivers used by ILT are highly dynamic, with substantive changes occurring across a wide range of temporal and spatial scales. River hydrology is the primary driver of sandbar morphodynamics in these systems. Better characterization of sandbar area over time accounting for varying flow regimes allows for a better understanding of landscape-scale ecology for sandbar-dependent species such as the ILT. This dataset seeks to quantify sandbar area which may be used by ILT at the landscape scale and how it has changed over time using remote sensing techniques. The assessment of landscape scale trends in sandbar area over time requires datasets with relatively high temporal resolution and long periods of record covering large geographic areas, and remotely-sensed datasets must also consider changes in river stage. Land cover classification datasets within active channel masks were developed using all available images from the Landsat Thematic Mapper (TM) series of satellites meeting cloud-free (40% or less) and ice-free criteria. Landsat imagery was selected because of its long period of record, spatial coverage, and regular reimaging cycle, making it well suited to monitoring ILT sandbar habitat over time. These datasets were also attributed by discharge or stage using a new database integrating U.S. Geological Survey and U.S. Army Corps of Engineers river data with Landsat metadata. This report documents development of these riverine classification datasets with a focus on applicability to the ILT. This framework may be used for continuing monitoring of ILT sandbar nesting habitat.