Sorry about the title - actually, this is about another bird of the genus Phalacrocorax, namely, the Cormorant.
Cormorants and geese are similar in size, and both fly in V-formations. So how do you tell them apart at long distance?
You can easily distinguish them at close range, but I was astonished when a friend (well, he is a nature reserve ranger) identified them as cormorants from hundreds of yards distance. For all I knew, they could have been pinkfoot geese.
Apparently cormorants sometimes stop flapping and glide, but geese never do (except when actually landing).
It's little things like this that make me realise how much I have to learn about the world around me.