I figured out a solution to my circle problem in case you're
interested. The result is similar to that of running s.menu, option
7 (convert site to raster - freq of occurrence) except the sites turn
into circles of a defined radius and the values in the raster are the
frequency of circles that circumscribe each grid square.
Since I had to repeat the process on 244 animal-season files each
containing up to 50 sites, I wrote a really ugly shell script to do
the work. Let me know if you're interested in seeing it.