Sept. 11–13. All invited to view chimney swifts gathering at dusk and count them as they enter their roosts in a spectacular swirling tornado of birds. Participants choose a known roosting location and report back to WBNA organizers. Part of a national effort to monitor the migration of this bird species and learn its favorite chimneys for overnight roosting. 8 p.m. until the last swift descends into its chimney. Various locations, preregistration required at washtenawbna.org/events. Free.