Trumpeter Swans are northern hemisphere birds, living in Alaska and Canada. So, their heavy down feathers keep them warm. If the swans are back together, the sick one got off the ice, made it through the night and is eating, they should be okay. The other swan would not jeopardize its safety to return if it sensed that severe weather was occurring and it could not leave or protect itself.

Please let us know how they progress. If something should look wrong with the swans after tonight, then you need to contact a waterfowl/wildlife rescue group to see if they can safely access the ice and attempt to rescue them. The Regal Swan