Nocturnal Flight Behavior of Waterbirds in Close Proximity to a Transmission Powerline in the Florida Everglades

Abstract

-Many birds move at night, and although there is strong potential for collisions with stationary structures, the behavior of birds in response to such structures is poorly understood. We studied the nocturnal interactions of waterbirds with a 550v transmission powerline in the flat, open landscape of the Florida Everglades using a combination of surveillance radar to detect incoming birds, and night vision optical equipment to observe flight behavior. During 118 hours of observation we recorded a total of 285 flocks of ciconiiform birds crossing the powerline during spring 1997. We visually observed 663 birds in 187 flocks, and documented their response to the powerline. We found that the flight directions and the colony site locality strongly suggested regular nocturnal foraging behavior of some species, especially Black-crowned Night Herons (Nycticorax nycticorax) and Wood Storks (Mycteria americana). Birds flying at night were less likely to react to the powerline, suggesting that powerlines may pose more of a collision threat during darkness. However, we also found that waterbirds flew higher at night than during the day and thus came into a zone of potential contact with the powerline much less often than during the day. Received 8 April 2001, accepted 3July 2001.