Radar has been used to study birds since the 1940s (Bellrose 1964), and has been especially useful to study migration and mass movements (Eastwood, 1967, Gauthreaux 1975, Russell and Gauthreaux 1998). Weather and air surveillance radars have been used to study bird migration over large areas, but they are not useful for collection high-resolution data over small areas. Marine surveillance radars, which are used on watercraft for navigation, have been adapted to monitor bird movements over land (Kerlinger and Gauthreaux 1984). Marine surveillance radars are relatively inexpensive, available off-the-shelf, require little modification, are easy to operate and maintain, have high resolution, and can be modified to obtain altitude data (e.g., Gauthreaux 1985, Cooper et al. 1991, Cooper 1996).
Despite the availability of radar technology, many studies of bird movements, including those involving impact assessment, concentrate on diurnal movements. However, in most areas, most birds migrate at night. Additionally, diurnal observations of bird movements may miss most birds that pass observation points. Thus, radar may allow a more complete assessment of movement patterns of birds than only visual observations.
We (1) discuss using marine surveillance radar to determine bird movements, (2) describe modification of equipment to enhance its performance, (3) describe procedures for data collection and analysis, and (4) discuss the sampling effort needed to provide reliable information. Our study was part of a pre-siting analysis for wind turbines at the Norris Hill Wind Resource Area in southwestern Montana (NHWRA).