Migration of many kinds of birds over Illinois as seen on radar on a typical night in springtime. Bird echoes cover most of the midwest on a night such as this; those visible on one radar extend only to a certain range because the radar beam goes straight whereas the earth curves down.

At this time (2136 CDT) the air is filled with nocturnal migrants and the radar beam encounters many of them everywhere it points. Most of the birds are songbirds (passerines) but other kinds of birds and some insects contribute to the echoes. The arrow points to a location 9 km (5.5 miles) north of Sibley, Illinois which is where a Swainson's Thrush was flying on a track of 344 degrees in spring migration. The bird took off from Urbana Illinois at 2039 CDT with a tiny radio transmitter that allowed us to follow it as it flew. This bird lost us over northern Wisconsin after 0300, probably to continue over Lake Superior right into Canada.

This image was obtained from the Department of Atmospheric Sciences at the University of Illinois. The original data were taken by an S-band National Weather Service Doppler radar located at Lincoln, Illinois.