Bedell Bridge State Park in Haverhill, NH has one of the prime floodplain forests in NH. Take a left just past the village before you get to Rt. 25 north of the center of Haverhill. You can spot birds in the wetlands along the road if you enter slowly.
There are several trails to explore from the parking area.
Here are some of the birds you might find in this wonderful, infrequently-visited state park without an entrance fee.