Birds on the move whirling confusion

摘要

Swallows and martins migrate en masse, yet few birders seem to notice. The milling, swirling, protean motion that I was witnessing looked like a blizzard. But it was August. And the swirling mass turned out to be roosting swallows and Purple Martins. They landed everywhere, from vegetation to transmission lines. I had seen swallows line up along electrical wires all my life. But nothing prepared me for the numbers of swallows I was observing at dusk this day, August 12, 1989. I was crossing the Maurice River Bridge -- midway between Wilmington, Delaware, and Cape May, New Jersey -- driving slowly because Bald Eagles, Osprey, otters, and other creatures often appeared there. As I cleared the top of the bridge, masses of swallows and martins stretched across the horizon. The birds were forming a communal roost just prior to their migration out of southern Jersey. They settled in primarily among phragmites -- tall, invasive marsh grass. Present were Barn, Cliff, and Bank Swallows, as well as PurpleMartins. Rough-winged and Tree Swallows might also have been there, but I didn't have the presence of mind to identify all of the species. I was too busy trying to figure out what I was looking at. As for counting them, that would have been impossible. Iestimated that a quarter million birds were present, but that number could have been off by 100,000 or more.