Large bodies of water, such as the Great Lakes in North America, are potential barriers to migrating bats. Islands may be used as stopover sites by bats crossing the Great Lakes as stopover sites, or included in crossing routes to reduce the distance flown over open water. I predicted that stopover use by migrating bats would result in higher activity on Great Lakes islands during late-season migration than at mainland sites. I monitored acoustic activity at 11 sites across four locations in Ontario: Amherst and Pelee islands, Kingston and Pinery Provincial Park during the summer (June and July), and during the putative late-season migration period (August and September). I found some evidence of migration by Lasiurus borealis and Perimyotis subflavus at Amherst Island, and by Perimyotis subflavus at Pelee Island. Islands may have occasional roles as stopover sites for migrating bats.