NexRad and bird migration

In the last post, I mentioned that migrating birds can often be picked up by radar meant for monitoring precipitation and other weather conditions.  Well, in the region of Pennsylvania and New Jersey tonight (April 10th), there isn't precipitation, but there certainly seems to be a lot of migrating birds!

You can see the large migration imagery in the center of Pennsylvania.  The radar images shows a coastal storm that is now over New England.