It sounds as if you are located near a migratory station. The swans have flown into this area for the winter from their northern habitat. The swans are eating in the field, resting and awaiting spring to return back to their habitat for the nesting season. This migratory station also affords families to migrate for the winter and introduce the juveniles to potential life-time mates for future pairing. When the swans return to nesting sites, the juveniles will form pairs and look for their own habitat to begin their future life as adult/parent swans. The Regal Swan