ARCTIC TERN

The amazing arctic tern flies from the Arctic to the Antarctic every year. It must hold the record of the longest annual migrations of any living creature. It is estimated that the round trip is about 35,000km.

It’s diet is fish and crustaceans such as shrimps. The Arctic tern lives and nests all around the northern hemisphere where food is in plentiful. They breed mostly north of the Arctic Circle all along the shore of Greenland, north of Canada, Alaska, Russia and on the polar islands. Some birds nest on the Tundra and feed on aquatic insects and fish in freshwater lakes.

Colonies have also been found further south around the Baltic, the North Sea, on shores of Britain, France, Ireland and on the eastern parts of the USA.

PROTECTING ITS NEST

Since the Arctic tern nests in cold windswept areas it is hard to conceal the nest because there are hardly any vegetation growing there. The tern chooses very open spaces and it is thought their main predators such as Arctic fox, skua or rats could be seen long before it approaches the nest.

It also nests in places on little off-shore islands where predators have to take the risk to swim in icy-cold waters. Furthermore, it nests with many hundreds or thousands of other terns. When there is a danger the birds take off and the pair circle over the nest.

When the predator is trying to attacks the nest the bird swoop down and pecks the head.  Surprisingly the tern can give a very nasty punch and will continue till the predator retreats with a bloody head. This also goes for humans who decided to wonder into the colony.

A great camouflage is that the eggs have blotchy dark brown pattern on light brown background which blends in perfectly with the surroundings. When a predator comes near a nest the chicks keep completely still while the infuriating parents are attacking the predator till it willingly retreats before it even spots the chicks.

NESTING SITE

When a pair of terns found a good nesting site with reasonable safety and plenty of food close by they will return to it year after year. They are capable of .finding their way back from the other side of the world.  Even the young birds return to the place where they were born. Gradually the colony is growing bigger and bigger until all the places are occupied.

The best place is at the centre of the colony because predators will hardly reach there with all the other terns around. However, these places are fought over and in great competition. Young birds that breed for the first time have to nest at the edge and as they get older they slowly move inwards.

BREEDING

Young birds usually start breeding when they are three years old but their first attempt ends mostly in failure. This is mainly because they are only getting a nesting site at the edge of the colony. The other reason is they have not got enough experience in catching enough fish to feed the young.  Arctic terns dive from a height of 10 m above the water and therefore it is easy for inexperienced young ones to miss the fish. Another problem is to bring it back to the nest. Arctic skuas are expert pirates and fly constantly over the colony ready to steal the fish from a tern. The skua gives chase and the tern is trying to escape but sometimes it drops the fish and the skua catches it while it falls.

FOOD

Although predators are a constant battle but most of the birds are raising their young successful. The bigger problem occurs where there is a food shortage. There can be a natural occurrence. It can happen that the small school of fish to not appear and although there is plenty of fish but they are too big for the chicks. Then there are freak gales which prevents the adults from flying to catch fish.

In recent years it happens quite frequently that the colonies in the north of Britain could not find enough food for their chicks. It is thought that over-fishing is the cause. A particular fish called sandeel which is the main food for terns is fished for producing oil and food for livestock.

MIGRATION

At the end of their nesting season the terns set off again on their incredible migration. It travels south as the summer ends in the northern hemisphere avoiding gales, cold and dark condition. When it arrives at the southern ocean it is summer there. The birds fly as far as the Antarctic pack ice will have daylight round the clock for fishing.

The Arctic tern can live up to 20 years and in view of these constant migrations it clocks up an enormous amount of mileage which is a great achievement for a bird weighing 100g.

ARCTIC TERN OVER
THE MENDENHALL