In 2010 we did not have a successful Montana Osprey Project. An Osprey did not nest on the platform. Instead a Canada Goose nested there, laid eggs, cared for her goslings and they fledged from the Osprey platform to the creek below.
In researching Canada Geese and Osprey platforms we have found that a Goose nesting on a platform is fairly common, especially if the platform is close to a good water source. There are even recorded cases of the Osprey chasing the geese away!
This BirdChick Blog has an interesting article about an Osprey nest with a rouge gosling on it.
Also we read that a good deterrent to keep the geese off of the platform until the Osprey arrive is to put a plastic garbage can lid, the dome shaped kind on top of the nest until Ospreys are spotted in the area.
Videos: Canada Goose and Goslings