A ring species occurs when two populations that are connected by a geographic ring of populations that can interbreed but do not interbreed despite living in the same region. Upon migrating to the Comoros, Grandidier's free-tailed bat and C. pusillius became sympatric. There is evidence of isolation between the two populations further restricting gene flow.[citation needed]
^Naidoo, Theshnie; Goodman, Steven M; Schoeman, M. Corrie; Taylor, Peter J; Lamb, Jennifer M (2016). "Partial support for the classical ring species hypothesis in the Chaerephon pumilus species complex (Chiroptera: Molossidae) from southeastern Africa and western Indian Ocean islands". Mammalia. 80 (6). doi:10.1515/mammalia-2015-0062. S2CID89517662.