Volume 4 (2008) Pages T9-T20
It is reported that a Wind Profiler (WPR), a meteorological radar for wind direction and speed, detects the echoes that are assumed to return from birds. We attempted to determine whether these echoes actually returned from birds at Muroran, northern Japan, which is located on one of the main bird migration routes between Hokkaido and Honshu. We recorded the number of birds migrating over the study site by counting bird flight calls and the number of birds passing across the moon surface at night as well as the number of birds flying past in the early morning for 6 days in the autumn seasons of 2005 and 2006. We also recorded bird echoes using a marine radar for 5 days in the autumn of 2007. We compared these results with the occurrences of "bird echoes" detected by a WPR, which is operated by the Muroran Meteorological Station. The occurrences of WPR bird echoes were significantly correlated with the bird numbers based on the four methods. The time and altitude patterns of "bird echoes" were also highly correlated between the WPR and the marine radar. These suggest that the WPR bird echoes returned from migratory birds. However, the WPR bird echoes underestimated the bird number in the early morning when the birds flew in dense flocks and overestimated the flight altitudes. Although WPR bird echoes have these defects, it was shown that they would make a major contribution toward the nationwide monitoring of bird migration because WPRs collect data at 31 sites across the country throughout the year except winter.