On Sanibel Island there are several man-made platforms which are used by Ospreys. A naturalist "Bird" Westal was instrumental in erecting these in the late 70's. It was a great success story and help restore Osprey populations which had been on the decline. A few years ago an Australian Pine which had housed the nest of  Bald Eagles died either from natural causes or from help of man. It was then a group decided to build a platform for the eagles. This year they built a nest and have hatched two baby chicks. I was told by a birding expert that this was the only one he had ever seen used by eagles.