Cormorant or Shag by behaviour (1 Viewer)

I was watching a variety of birds including Cormorants and (maybe) Shags at Portland Bill on Sunday. The birds were a fair distance away and some might or might not have been Shags. Now, somebody pointed out that as, e.g. in the Collins guide, the Shag "Dives with more pronounced leap clear of water". How reliable is this if you see a bird that could be a Shag or a silhouetted and perhaps especially energetic Cormorant?

Anybody know what it is about the Shag or Cormorant lifestyle that causes this difference in behaviour?

I would say that the leaping behaviour is useful but not really diagnostic. It can be quite noticeable sometimes with Shags but they don't always do it. It also varies depending on the conditions of the water. So useful but use with caution.

I think jumping out of the water is a pretty certain indicator of Shag - I've never seen a Cormorant do so. As Andrew says, Shags don't always jump, so the converse (that one which doesn't jump is a Cormorant) isn't true.

Michael