Here are close-ups the the radar loops out of Colchester, Vermont from http://www.rap.ucar.edu/weather/radar/displayRad.php?icao=KCXX&prod=bref1&bkgr=black&endDate=20091011&endTime=-1&duration=0 and Ft. Drum, NY from http://www.rap.ucar.edu/weather/radar/displayRad.php?icao=KTYX&prod=bref1&bkgr=black&endDate=20091011&endTime=-1&duration=0.
The "starburst" or "donut" of blue and green colors surrounding the radar sites are typical of birds, as opposed to weather. To confirm that these are birds, one can click on the radar image to obtain a velocity image as seen here:
and here:
Things are moving from the N and NW (represented by the blues and greens - objects approaching the radar) to the S and SE (represented by yellows and oranges - objects moving away from the radar). This is the expected direction of migrants on a night with calm or northerly winds at this time of year. (Also, the colors on the radar images only appeared after dark, when most birds are migrating.) Therefore, we can conclude that the colors appearing on the radar are mostly, if not all, birds. Step outside in an otherwise quiet area on a night such as tonight and you will surely hear birds passing overhead. See Brian McAllister's August 21 post on the subject of identifying nocturnal migrants by their flight calls :http://adknature.blogspot.com/2009/08/new-way-to-birdwatchor-listen.html.
For more detailed primers on birds and radar see Derek Lovitch's blog at http://maineoutdoorjournal.mainetoday.com/blogentry.html?id=7065, David La Puma's Woodcreeper site at http://www.woodcreeper.com/ (and especially http://www.woodcreeper.com/2008/08/28/birds-on-the-move-over-nj/), and this Clemson University site: http://virtual.clemson.edu/groups/birdrad/COM4A.HTM.
