An especially popular destination for birders, the Concord portion of this 3,800-acre refuge includes 2.7 miles of walking trails along the sleepy Concord River and across a flat dike between man-made ponds that attract abundant wildlife. At a board at the entrance, visitors jot down the birds and other creatures they have seen. More than 220 species of native and migratory birds have been recorded, including red-winged blackbirds, great blue herons, and bald eagles. Dogs are not allowed. Parking is limited.