Biology Reference
In-Depth Information
A
It's true. Weather radar images show where radar beams have been “reflected” as they
sweeptheatmosphere.They'reusefulforshowingweatherconditionsbecausethebeams
arereflected byprecipitation andthewater vaporinclouds,buttheycanalsobereflected
by swarming masses of birds or insects.
In the early days of World War II, British radar operators noticed mysterious, ethereal
shadows drifting across their screens. They weren't associated with weather systems and
so the radar technicians nicknamed them “angels.” In 1958, a New Orleans high school
student named Sidney Gauthreaux, realizing that these “angels” were really the radar
reflections of swarms of birds, started scrutinizing radar images. As a Louisiana State
graduate student, he worked with radar images to document the existence of massive
trans-Gulf migrations.
Inthelate1980s,Gauthreauxstartedexaminingarchivalradarimagesandmadeadis-
turbing discovery: major bird movements over the Gulf had declined by nearly half since
the 1960s.
Next Generation Radar (NEXRAD) made studying bird migration much easier. The
AirForcestartedusingittoavoidcollisionsintheirBirdAircraftStrikeHazardprogram.
Graduate students took stunning images of giant expanding aerial doughnuts, which they
found to be thousands of Purple Martins radiating from critical roosting sites each morn-
ing.
Nowit'seasyforanyonewithaccesstoaNEXRADweathermapontheircomputerto
see birds take off on migratory movements at night or alight in the morning, if you know
how to interpret the mystifying patterns. You can learn how at
www.virtual.clemson.edu/
THE DANGERS OF MIGRATION
Fall migration,
when many birds fly over the Gulf of Mexico, takes place during hur-
ricane season. Birds can be killed outright by high winds, hail, blowing debris, falling
trees,andsoforth.Theycanbeblowntoofaroffcoursetosurvive.Birdspassingthrough
a devastated area after a storm may have trouble finding feeding resources, or may
succumb to pollutants released in hurricane-related oil, gasoline, and other toxic spills
caused by flooded automobiles, households, oil refineries, chemical manufacturers, and
other sources.
Most migrants don't encounter hurricanes and avoid damaged areas. But there are
plenty of other dangers out there. Communications towers in their flying space may kill
as many as 50 million migrating birds per year. Occasionally in foggy or stormy weath-
er when birds are flying over open water in the Gulf or the oceans, they are attracted
to the lights of a lighted vessel and dash against the windows, injuring or killing them-
