Razorbill (Alca torda)
They are not easy to get close to from the heights of the cliffs as they nest on the lower edges and this is about as good a view as I have ever been able to get. It does show the two features, however, that enable you to pick them out from amongst the many Guillemots.
Firstly, and usually the most obvious feature, is the Razorbills razor bill! The Guillemot has a much more pointed bill whereas the Razor bill has a much bigger, chunkier beak.
The other feature, when the light is good, is that the Razorbill is very much darker, almost black, on its back whereas the Guillemot is chocolate brown.
The two species are both members of the Auk family (along with Puffins of course) and they are often seen together and so obviously get on well together