We did a little research and found that this mixture is indeed provided to waterfowl and poultry, mainly ducks, geese and chickens. We cannot find any reference to swans, but as long as the mixture does not have a high protein content and the swans will eat it as a supplemental winter food source, then there should be no problem.

Some research notes that even geese will not eat the oats as this is an acquired taste, much like lettuce is to some swans. Again, as long as there is not a high protein content, the food mixture should be fine. The Regal Swan