Thanks to all replies for the advice.
Paul - actually it is the Isle of May I intend going to. You reckon the 70-200mm is adequate? Do you think the 17-40 would be of any use? A monopod might just be one more thing to faff about with.
The folk doing these tours supply waterproofs and I was going to take a hat anyway.
Must remember never to look up with my mouth open.
Yep, I use a crop camera, so it its that bit more tele, but to be honest with todays resolutions, you'll be fine, the slightly wider shot gives you some environmental context too, it's a beautiful place, and if you want closer you can always crop.
I would emphasise choose one or the other.
Another valuable lesson: The boat that takes you out has gunwhales below the benches where waves crash in. My bag got soaked, thankfully a billingham, the contents were bone dry. Don't sit your gear at your feet.
The terns will peck at your head on the way in and way out, so the hat is essential, as is a monopod to carry over your shoulder slighty elevated. It was the poo that got me though, I needed an eye flush on the way back, thankfully the excellent chippy distracted me at the far end.
It's a great wee day out, there are a few lighthouses of different generations on the island, not spectacular enough to make for great landscape shots, and you'll like ly be there early afternoon too!
I would take a monopod, one big lens (I suggest the 70-200) a spare battery and spare card and enjoy. Spend some time looking at the birds with your eyes rather than just through the viewfinder, the less gear you have, the less time you spend tinkering.
Quite jealous recalling it.