Sea Fishing is one of my main hobbies and as a result I've spent a lot of time on boats often 20-30 miles off shore and it's surprising how many times we've had birds "hitch" a lift. Mainly racing pigeons but also many other species who settle down in a sheltered spot, though I've never seen one land on anybody, and seem to be quite happy so stay until we sight land again then off they go none the worse for a few hours at sea. Still as you say there must be thousands who sadly don't find a happy landing place and become lost at sea.