Is there any way that you can break some ice to provide them with water? The swans need to have about 20-30 feet in diameter of open water. They need water to feed and drink. If you add food on the ice you may invite predators onto the ice to access and kill the swans. By breaking the ice in the above measurements, the birds can have a place to seek shelter from predators. They can also starve without food. So supplementally feeding them will help. A mixture of cracked corn, poultry layer pellets, lettuce and a small amount of bread will help them. If you cannot break the ice, you need to provide a water bowl next to the food bowl.

On another note, is there anyone in your area that might be able to capture the swans and relocate them to another pond? Can they fly? This is a major consideration if a capture is tried because they may fly away which would not be a bad thing as they could be chased to an unfrozen pond. The Regal Swan