Burhinus
Here is the article on tern ID.
In the interest of copyright this was first posted by Martin Collinson on UK.Rec.Birdwatching.
From: Martin Collinson
Newsgroups: Uk. rec. birdwatching
Sent: 11 June2001 21:02
Subject: Re: Quick ID of terns?
William Hewitt wrote
Watching terns from a distance, without decent bins or a scope, are there any easy ways to tell them apart?
It depends how far away you are, but...
Sandwich terns can look very white, and the grey of the primaries rather messy. They have an irritating partridge-like croak of a call, not nearly as pleasing as the other terns. The short tail and (apart from early spring) white forehead stand out from quite a way away, and these are the easiest terns to identify. They are also quite big.
Common/Arctic/Roseate terns are more difficult from any distance, when you can’t see the classic plumage differences. Look at the flight patterns when feeding. Arctics can never make up their minds whether to dive or not -classically they swoop down, stop, hover close the surface for a second, and then splosh in. Commons on the other hand tend to be much more decisive -fly, bank and splosh! Arctics have a lower body mass, with the airy bouncy flight that goes with it, although Commons can be airy with the best of them.
Roseates are easier to separate from the other two - they have a more fluttery fast-winged flight like little tern, look pale like Sandwich terns and a distinct way of diving- fly along, then head down and fly into the water almost. Easily picked out in a mixed flock of terns.
All these terns, like all birds, can do as they damn well please, so these are only guidelines. Without experience, everyone finds terns difficult, but you are probably the best placed person in the World for getting them sorted out!
Cheers
Martin