Geo-Marine, Inc. (GMI) conducted an offshore avian radar baseline study for Oregon Wave Energy Trust (OWET) for a wave energy study located northwest of Reedsport, Oregon from 25 August through 29 October 2010. The study was conducted from shore with GMI’s Mobile Avian Radar System (MARS®). The MARS® was equipped with a 3-centimeter (cm) wavelength 50-kilowatt (kW) radar with a 2.5-degree (°) parabolic antenna for horizontal scanning, and a 3-cm, 25-kW radar with an open array antenna for vertical scanning. Diurnal land-based nearshore and diurnal and nocturnal boat-based radar validation surveys were conducted specifically to determine whether the radar could detect birds flying at low attitudes above the water. Comparison between the nearshore and offshore (study area) observer bird passage rates and the nearshore and offshore radar passage rates revealed low correlation between diurnal observations and radar data. The correlation analysis values were all too low (<.307) to develop a correction factor to apply to the radar data. Sea clutter was identified as the limiting factor. When algorithms to reduce false tracks from sea clutter were applied, tracks of real birds were eliminated because they could not be separated from sea clutter false tracks. At present there is no technology known that can accurately remove bird detections from sea clutter. This problem was further magnified in this study because radar visual validation surveys revealed that a major portion of the bird movement both nearshore and offshore occurred at altitudes from 1-30 feet (ft) above sea level. At that altitude it is impossible to separate birds from wind-driven waves and high swells that are common in the study area during fall. The visual validation data documented that the radar was ineffective when birds were flying close to the surface. In addition to providing data to facilitate passage rate comparisons between observer and the radar, the radar validation surveys provided data on bird flight behaviors within and adjacent to ...