In October 1989, researchers at the U.S. Army Engineer Waterways Experiment Station (WES) initiated a project to investigate the historical loss of critical whooping crane (Grus americana) habitat on the Aransas National Wildlife Refuge. Vegetation on the area was categorized into 11 habitat types and manually delineated on aerial photos of the area from 1930, 1957, 1986, and 1988. Habitat type maps for each year were digitized into a Geographic Information System (GIS) database that included soils, topography, and National Wetland Inventory data. Preliminary GIS analysis of habitat type data indicated a progressive loss of 2 habitat types, tidal flats and tidal ponds, and a gradual increase in the marsh vegetation type. In 1930 and 1957, tidal flats comprised approximately 7% (454 ha) and 8% (500 ha) of the study area, respectively, but that number decreased to approximately 2% (134 ha) of the area in 1988. Marsh vegetation covered approximately 18% (1,214 ha) of the area in 1930, 17% (1,123 ha) in 1957, and 21% (1,369 ha) in 1988. A decrease in the number of semi-permanent ponds was also observed from 1930 to 1988.