The Waltham Land Trust, a private nonprofit organization dedicated to preserving open space in Waltham, is inviting local residents in this year’s annual duck sightseeing tour along the Charles River in Waltham on Jan. 27 at 10 a.m. A variety of northern-dwelling ducks migrate south from Canada during the winter months to live on local waterways, according to the organization. Local birders who frequent the Charles River will lead the walk and help attendees identify the types of ducks in Waltham. Last year, walk participants saw nearly every variety of winter waterfowl, including a bald eagle, the organization said. Interested individuals will meet behind Shaw’s Supermarket at 130 River St. in Waltham, next to the Mary T. Early footbridge that extends over the river. Walkers are encouraged to bring binoculars and dress warmly, and must be able to stay quiet and observant. The walk, which is free and open to the public, is part of an ongoing series of events hosted by the Waltham Land Trust designed to highlight the city’s many open spaces.