More than likely it was on the migration path and got sidetracked. It will probably get something to eat, rest and then continue on its path. You probably do not want to keep the bird around if this is the case as it will not be familiar with the area, i.e., will not know about resident predators and how to escape and will not have a chance for finding a mate in the future.

The only way that the swan is going to stay is if there is ample food, shelter and nesting resources as well as safety from inclement weather and predators. Depending on your state rules and the species of the swan, it may be illegal to feed it to provide it with ample food resources. Food is a great attractant, but not necessarily something that will guarantee that it will stay in the area, especially without the possibility of a future mate. Give it a couple of days if not a week or so and it will probably move along. The swan will want to go back to its familiar habitat and other swans.

The best thing to do is nothing because if it stays without human intervention, then it will likely stay in the area. If this is the case, you might think about providing it with supplemental food etc. at that time. Again only if it is legal in your area. The Regal Swan