Can you identify the circular features that appear below?

The answer, according to the following link: http://cimss.ssec.wisc.edu/goes/blog/
About 25 minutes after the time of the IR images [shown on the aforementioned link], an interesting meteorological radar signature of bird “roost rings” was observed. Large numbers of birds dispersed from their nocturnal roost sites during the early morning hours to begin feeding, and as the flock crossed the radar beam, ring-like signatures were seen on the Milwaukee/Sullivan radar composite reflectivity product as the birds spread out across the area. Similar radar signatures are also occasionally seen with bat swarms.
At least two of the roost rings appear to have originated from the general vicinity of some of the larger (warmer) lakes noted on the MODIS and GOES IR imagery: Beaver Dam Lake (located northeast of Madison, KMSN), and Lake Koshkonong (located southeast of Madison). As close as one of the larger roost rings came to Dane County Regional Airport in Madison, one also has to wonder if the high density of birds may have potentially been an aviation hazard for a brief period of time?