A large group of birds was detected leaving Green Island on Green Bay to feed just before sunrise on August 10, 2006. This radar signature, known as a "roost ring," occurs as thousands of birds leave their roost and fly into the air. The roost ring expands until the birds begin foraging after dispersing.
Below is an eight-image animation of radar reflectivity from the NWS Green Bay Doppler radar. The first radar picture is taken at 5:25 AM; the last one about 6:15 AM. (Animated GIF image.)
Another example of a roost ring from Green Island was documented in August 2010. Click here for more on that event.