The Barn Swallows are gathering once again (as they do every year) in large numbers at their staging area along the Willamette River in Yamhill County, Oregon. In past years the number has appeared to reach at least several hundred thousand, and on clear mornings can even be detected by the weather radar installation near Portland. Below is an image from a short loop recorded a few days ago on the morning of Sept. 4, 2010. The bright green, small "bubble" near the lower center of the frame is the radar "picture" of thousands of birds dispersing from their nighttime roost in a cornfield. The flock apparently moved eastward as the birds left the field, which is west of the river. The radar did not detect them until they had gained some altitude.
To read more about this phenomenon in an account published by biologist and researcher, Bruce Cousens, please go to the following link:
Back on September 12, 2006, I photographed part of the Barn Swallow flock as it ascended from the cornfield on Grand Island in Yamhill County just as dawn was breaking. It took only a minute or two for the entire flock to disappear from sight. Click on the photo below for an enlarged view, and you should be able to see the thousands of small specks against the morning light.