A Radar Investigation of Extremely Low Frequency Electro Magnetic Fields on Free Flying Migrant Birds.

High resolution, low power radars detected movements of migrant birds over the Wisconsin Test Facility (WTF) during the fall of 1974 and 1975 and spring 1975. Observations indicated that (ELF) emissions of the WTF in its present configuration with MSK modulation is unlikely to have a major impact on the orientation of birds migrating over the site. Preliminary analysis indicates, however that some birds may be sensitive to ELF emissions. Search radar data indicated a change in average flight direction of 5 to 25 deg when the N-S leg of the antenna is activated. Tracking radar studies revealed that an increased tendency of birds to depart from straight and level flight was associated with ELF exposure. While both tracking radar and Ornithar indicate that change in migratory direction due to activation of the WTF antenna is likely to be small, demonstration of any effect of ELF on free flying migrant birds represents a significant addition to knowledge of the orientation systems used by birds to guide migrations. Present data indicate no effect of distance within the operational range of the radars (1 km in the present experiment). Without further information on at least duration and distance effects, the writers believe it unwise to extrapolate present data to a full scale antenna grid system.