Every Thurs., Sept. 3–Oct. 29. WBNA members lead a hike through the Arb to look for fall warblers and other southbound migrants. Birders of all skill levels welcome. 8–11 a.m., meet in the cul-de-sac at the end of Riverview. (off Geddes near the east end of Dow Field). Free. washtenawbna.org.