I created a Google Earth / Google Maps file of all the Christmas Bird Count Circles in Maryland (those whose centers occur in the state). I hosted the file on my website
http://www.westernmdbirding.com/
http://tinyurl.com/MD-CBCs
I downloaded all the circle centroids from
The National Audubon Society and imported them into ESRI's ArcMap software to create a shapefile. Then I created a second shapefile that was a buffer of those points with a buffer distance of 7.5 miles. Then I exported the second shapefile into KML using
KMLER.
I also found a link that describes another method in case you want to do this without using GIS.