Beavers at Dusk. Mass. Audubon Society Ipswich River Wildlife Sanctuary. 87 Perkins Row. Topsfield. 7:30 p.m. to 9:30 p.m. For families with children 5 years and older. Take an evening walk to a beaver pond to discover beaver dams, lodges, and perhaps even a real live beaver. $10 adults, $8 children (discount members). Registration required. 978-887-9264. www.massaudubon.org