Nice photo. Styrofoam may not be stable, i.e., it can flip and wind may cause the nesting contents to be blown from the area. Additionally, the swans may peck and try to eat the styrofoam which can cause choking or toxicity. The swans may need some type of shade, however, they do not usually like unatural fixtures over their heads. Placing a tree or natural bush, shelter on the styrofoam is going to be an even worse headache.

Bushes and grasses are the swans natural shelter as well as protection from most predators. However, if a coyote or fox wants to get at the swans, there is not much that you can do except possibly electrify your fence, above and below so that the coyotes cannot dig under or climb over the fence. Just make sure that an electric fence is legal in your state and the fence is on the outside fencing so that the swans do not come into contact with the electricity. The Regal Swan