This would indicate that something is possibly wrong with the young swan, i.e, it is too small, feathers not completely grown or it may be ill as to why it did not fly away with the rest of the family.

Has anyone taken a boat out to see if the swan may be trapped by fishing line or something else which is why it cannot move from the area or is constantly dunking its head. It may be trying to release itself from an entanglement.

If you can get the swan to get friendly with you,( i.e, feed it bread and see how close it will come up to you} then it needs to be captured and relocated to a warmer area or wildlife/waterfowl rehabilitation center. It will probably not survive a severe winter, especially if it is constantly looking for food. Food resources (aquatic vegetation) is extremely limited during the winter and the swan can die from starvation. Does the pond have an aerator/de-icer? If not, the bird can not only die from starvation, but can fall between the ice and drown because it cannot get back onto the frozen area of the pond, and predators can access the bird by walking across the pond.

If the swan will not come to you, then someone needs to go out in a boat and see if they can either capture it from the boat or move it to an area where it will go on the bank in an area that it can be readily captured (i.e., a corner of a house, or a temporary pen). Just ensure that the swan is not chased into a dangerous area that it can become entrapped with its neck or forced over a steep ledge. If you can get a couple of people and force the bird into a bushy area, you can probably capture it more easily as long as it is not a dense forest type situation.

You can still supplementally feed the bird with lettuce, poultry layer pellets and cracked corn. However, if the swan does not stay in the pond at night to sleep, it will succumb to predation. The Regal Swan