I've never had any birds on the spreaders. My masthead despite being in prime Osprey territory, is a rounded top with a light. There's no perch. Better options are nearby. I suppose it's all location in the harbor, around other boats, type of local birds, etc.

But my boom, all 19' is too inviting. If I don't string a line above it, I'll have a mess or three to clean up from some good sized birds. The string(1/4") about 12" above, is all it takes. No landing room.