In Wales we are lucky enough to have a handful of rare tern colonies where birds return each year to breed and nest before migrating again in late summer.

Cemlyn Bay and the Skerries on Anglesey as seen in Springwatch 2009 are two very special locations in Wales and home to large colonies of arctic and sandwich terns.

Common, roseate and even sooty terns have also been spotted here over the years.

Terns are often referred to as the 'swallows of the sea' and are aerial specialists, living life on the wing and travelling thousands of miles in their lifetime to return to their breeding grounds each year.

You'll often see terns out at sea, hovering high above the ocean before folding their wings back and plunging at high speed into shoals of startled fish and sand eels.

They travel at astonishing speeds and back on land, will often fly very low along the ground like swallows.

When startled, the colonies will 'dread'. 'Dreading' involves hundreds of birds leaving the ground 'en masse' and flying in a series of formation loops around the nest site before returning to the ground.

No-one is sure why they do this, as sometimes it just occurs randomly, whilst other times it is clearly done as a defensive manoeuvre against aerial predators such as herons, gulls and birds of prey.

Terns will nest anywhere they feel safe and build fairly inadequte nests on the ground, often consisting of no more than an indentation in the gravel.

They will however defend their nest sites vigourously so don't get too close or you'll be attacked and excreted upon from a great height.

Due to their similarity in colour and astonishing speed on the wing, it can be difficult to identify between the various species.

Rough guide to identifying terns

• Arctic terns are white/grey in colour with a black cap, red feet and a red bill.
• Common terns look very similar to arctic terns with a black cap and red feet but have a red bill with a black tip.
• Roseate terns are whiter than the common and arctic and have a pinky underbelly hence the name. Their bills are black with a reddish tinge near the head which develops during the breeding season.
• Sandwich terns are very white with a black cap, long black bill with yellow tip and short black legs.
• Sooty terns have a white forehead and black cap with a black line running from eye to bill. On top they are a dark grey in colour with a deeply forked tail and wings.