Not sure what is your itinerary but the North Sea can be variable, as I wrote on a previous post: ' I've often found the North Sea a bit hit and miss, sailing from Southampton, although on both cruises this year there was plenty to see on the first day traveling north and the last day sailing south. When it gets really rough and you're furthest from land the Fulmar always saves the day turning up when all other birds have been left far behind- closely followed by the good old Gannet.''
On one cruise a Peregrine Falcon landed on board for a brief spell in the North Sea
From my vacation forum report '
A 14 night Cruise from Southampton to Norway and Iceland, 22/6/23 to 6/7/23.':
''First two days at Sea: We spent the first two days heading towards Norway passing through the North Sea. It’s not unusual to find an avian stowaway on board, this voyage was no exception. A Blackbird had taken refuge and spent the next two days with us until it departed to start a new life in Norway.
The first day was the more productive of the two with regular sightings of Northern Gannet, Northern Fulmar, some Guillemot and a few Kittiwake. There were less birds around the second day, mainly Northern Gannet and Northern Fulmar. ''
I've submitted a report of cruising and birding generally, on the Vacation forum. It's near the top on the first page headed 'Cruising and birding'