The “Exodus” on Radar; Bird Migration

April 24, 2012

Every Spring and Fall I get emails skeptical of my comments about “migrating birds” cluttering up the radar. They do. Many birds prefer to migrate at night because of a more stable air mass, and less turbulence from rising/sinking motions associated with the diurnal surface warming.   Apparently the sudden rise of birds immediately following sunset is called “The Exodus” (without Charlton Heston of course) since thousands of birds across any one region rise up at the same time into the lower layers of the atmosphere.  And it only takes a few birds in each cubic kilometer to get a “hit” on the radar.  So it’s not like a wall of birds is moving through the air.  This should look familiar if you watch the radar on fair weather Spring evenings:

Around here, I notice it starts in February and ends in June, then returns again in September and is done by November. It seems that the Spring migration takes much longer than Fall. Maybe they wait until the last-minute when it gets chilly up north and the bolt for warmer climates as fast as they can (like people).  There is an entire group of researchers at Cornell University that have studied this phenomena…check out the graphics here that explain how the birds show up on radar. Just keep hitting the NEXT on the bottom to progress through the explainers:

http://virtual.clemson.edu/groups/birdrad/COM4A.HTM

By the way, there is a movie called WINGED MIGRATION (a documentary) produced about 10 years ago using hand-raised birds. They follow the birds (usually geese) while flying and migrating using some sort of very light aircraft. Or, actually I suppose the birds follow the aircraft since they imprinted on humans at hatching.  That means they think humans are part of their family. Now, believe me, this is no “party movie”, actually it’s REALLY slow, but great visuals for little kids to watch. Filming was done all over the planet. Here’s a clip for a little mid-day relaxation:

I like how they have short conversations with each other while flying. 

The twice-yearly migration of millions of birds across the face of our planet is one of the most amazing displays of nature don’t you think?

Chief Meteorologist Mark Nelsen