Monitoring Shorebird Habitat Using Softcopy Photgrammetry: The Case of Western Snowy Plover in the Coal Oil Point Reserve, Santa Barbara, California

Abstract

Abstract The goal of this study was to determine how softcopy digital photogrammetry can be used to describe and monitor shorebird habitat. I focused on applying monitoring methods previously used for beach erosions studies of tourist beaches to shorebird habitat concentrating on the habitat requirements of Western Snowy Plovers. I investigated how the physical habitat of Western Snowy Plovers has changed over time at Sand Beach, which is part of Coal Oil Point Reserve in Santa Barbara, California, from 1928 to the present day, using width, area, and elevation data gathered from a series of aerial photographs. For two-dimensional analysis, I used single georeferenced photographs to measure width at regular intervals and area for each year a photo was available. Next, for three-dimensional analysis, I employed digital elevation models (DEMs) built from stereo photographs to explore whether the available photos can be used to document changes in the elevation of Sands Beach. The results were mixed. Georeferenced aerial photographs can be used to obtain quality measurements of beach area and width. Orthorectification is not necessary if photos can be georeferenced with minimal error. The amount of error present in the georeferenced images was indicated by the root mean squared error. A higher root mean squared error in the referencing process resulted in lower accuracy. Given the available photos and ground control points, I was unable to build digital elevation models with high enough quality to compare elevation from one year to the next. This was more likely due to a need for more ground control points than to the image scale or image errors. The area of Sands Beach was found to be increasing in area. This was due mainly to the retreat of the vegetation line as the mouth of Devereux Slough shifted in 1992 rather than an accumulation of sand on the beach.