Here is a comprehensive site of bird and radar research from Clemson. There is a page on roosting rings illulstrated by Purple Martins. Some years ago (5-10) when I lived in Columbus there were some posts on locating Crow roosts by from the rings produced in early morning and in evening. Perhaps they can be discovered from searching the archives. http://virtual.clemson.edu/groups/birdrad/index.htm Rich Richard Cressman East Boston, MA r.cressman.xyz.1928[at]gmail.com ______________________________________________________________________ Ohio-birds mailing list, a service of the Ohio Ornithological Society. Our thanks to Miami University for hosting this mailing list. Additional discussions can be found in our forums, at www.ohiobirds.org/forum/. You can join or leave the list, or change your options, at: http://listserv.muohio.edu/scripts/wa.exe?LIST=OHIO-BIRDS Send questions or comments about the list to: [log in to unmask]