The straw is going to get wet regardless of rain, sleet or snow. Once the mother goes out into the pond and then sits on the eggs, she is wet and will transfer that moisture to the nest. This moisture and her body heat is what causes the humidity along with the rotation of the eggs to incubate the eggs. The eggs need moisture and humidity to hatch. So, once the nest is built or in the process and especially if there are eggs, any disturbance of the nest may cause the swans to completely give up on nesting or try to find a quieter undisturbed area. It is best to leave it alone. No, swans do not like anything over their heads. If they do not nest under a bush or tree, they are not going to accept anything over their heads. The Regal Swan