I mounted the owl on the roof at my loft to scare away a group of pigeons for nesting in the eave. Initially, the pigeons were very afraid and didn't come back. Then one brave pigeon figured out that it was plastic and wasn't going to eat them. One by one they came back. Once I moved the Owl to another position, it scared the pigeons away again. It doesn't work on its on. I used netting to prevent the pigeons from getting into to eave. The owl seems to keep them off my skylight.
Cormorants sometimes use the bow of my 16' whaler for fish-spotting, and as an outhouse. This well-made, fierce looking owl made no difference. First day, lots of guano right next to the owl. Etc, etc, etc.