Hybridization, when it occurs, generally occurs between sibling species, closely related species that recently, geologically speaking, descended from a common ancestor. Think blue-winged and golden-winged warblers, as well as spotted and eastern towhees, crosses of which produce fertile hybrids. Gray squirrels are in the genus *Sciurus*, which includes among other species fox squirrels (*Sciurus niger*), a larger, more orange version of the gray. Fox squirrels are a Midwest and Southeast species; they occasionally hybridize with gray squirrels. Red squirrels do not. They are in a different genus, *Tamiasciurus, *and thus more remotely related to gray squirrels*. *Squirrels are all in the same family, *Sciuridae, *which also includes woodchucks, ground squirrels, and chipmunks*.* To post messages, send e-mail to: [log in to unmask] Set your e-mail application to PLAIN TEXT ONLY to post messages. To contact the list owner: [log in to unmask] To unsubscribe: E-mail this command to [log in to unmask]: UNSUBSCRIBE UV-Birders To change your e-mail address: E-mail this command from your old address to: [log in to unmask]: CHANGE UV-Birders [new e-mail address] Web based archives and subscription management are available at: http://listserv.dartmouth.edu/Archives/uv-birders.html