Join an expert birder for a guided bird watching trip through Blackwater National Wildlife Refuge on May 13. Whether an experienced birder or just a beginner, guides help everyone enjoy the many species of birds that live in or migrate through the refuge. Bring binoculars and field guides and dress for the weather. There is no cost for this activity and no preregistration is required. All walks begin at 8 a.m. from the Blackwater National Wildlife Refuge Visitor Center, located at 2145 Key Wallace Drive in Cambridge. Call 410-901-6124 for further information.