SATURDAY CRITTERS -Arctic Tern on Copeland Island (6)

You may all remember when we arrived at the island, I showed you the video of the Arctic Terns taking to the air and attacking  us.  Well today I am showing you photographs of them on their nests (from a safe distance!)

The Arctic Tern (Sterna paradisaea) is a sea bird of the Tern family Sternidae. This bird has a circumpolar breeding distribution covering the Arctic and sub-Arctic regions of Europe, Asia, and North America (as far south as Brittany and Massachusetts). The species is strongly migratory, seeing two summers each year as it migrates along a convoluted route from its northern breeding grounds to the Antarctic coast. Recent studies have shown average annual round trip lengths of about 44,300 miles for birds nesting in Iceland and Greenland and 55,900 miles for birds nesting in the Netherlands.  These are by far the longest migrations known in the animal kingdom. 

Arctic terns are medium-sized birds. They have a length of 13–15 in and a wingspan of 26–30 in. They are mainly grey and white plumaged, with a red beak (as long as the head, straight, with pronounced gonys) and feet, white forehead, a black nape and crown (streaked white), and white cheeks. The grey mantle is 305 mm, and the scapulae are fringed brown, some tipped white. The upper wing is grey with a white leading edge, and the collar is completely white, as is the rump. The deeply forked tail is whitish, with grey outer webs. The hindcrown to the ear-coverts is black.

Arctic terns are long-lived birds, with many reaching thirty years of age. They eat mainly fish and small marine invertebrates. The species is abundant, with an estimated one million individuals. While the trend in the number of individuals in the species as a whole is not known, exploitation in the past has reduced this bird's numbers in the southern reaches of its range.

The Arctic tern is famous for its migration; it flies from its Arctic breeding grounds to the Antarctic and back again each year, the shortest distance between these areas being 12,000 mi. The long journey ensures that this bird sees two summers per year and more daylight than any other creature on the planet.  

One example of this bird's remarkable long-distance flying abilities involves an Arctic tern ringed as an unfledged chick on the Farne Islands, Northumberland, UK, in the northern summer of 1982, which in October 1982, just three months from fledging, reached Melbourne, Australia. Assuming a direct route of flight, the distance covered would have been more than 14,000 miles.  

Another example is that of a chick ringed in Labrador, Canada, on 23 July 1928. It was found in South Africa four months later.

Arctic terns are long-lived birds that spend considerable time raising only a few young, and are thus said to be K-selected.  The maximum recorded life span for the species is 34 years,  although the average lifespan is about 20 years.  A study in the Farne Islands estimated an annual survival rate of 82%.

A 2010 study using tracking devices attached to the birds showed that the above examples are not unusual for the species. In fact, it turned out, previous research had seriously underestimated the annual distances travelled by the Arctic tern.

Eleven birds that bred in Greenland or Iceland covered 44,100 mile on average in a year, with a maximum of 50,700 miles. The difference from previous estimates is due to the birds' taking meandering courses rather than following a straight route as was previously assumed. The birds follow a somewhat convoluted course in order to take advantage of prevailing winds.

On average Arctic Tern will, based on the above research, travel some 1.5 million miles during its lifetime.

Breeding begins around the third or fourth year.  Arctic terns mate for life, and in most cases, return to the same colony each year.  Courtship is elaborate, especially in birds nesting for the first time.  Courtship begins with a so-called "high flight", where a female will chase the male to a high altitude and then slowly descend. This display is followed by "fish flights", where the male will offer fish to the female. Courtship on the ground involves strutting with a raised tail and lowered wings. After this, both birds will usually fly and circle each other.

Both sexes agree on a site for a nest, and both will defend the site. During this time, the male continues to feed the female. Mating occurs shortly after this.  Breeding takes place in colonies on coasts, islands and occasionally inland on tundra near water. It often forms mixed flocks with the Common Tern. It lays from one to three eggs per clutch, most often two.

It is one of the most aggressive terns, fiercely defensive of its nest and young.  It will attack humans and large predators, usually striking the top or back of the head.  Although it is too small to cause serious injury to an animal of a human's size, it is still capable of drawing blood, and is capable of repelling many raptorial birds and smaller mammalian predators such as foxes and cats although there are none of these on the Copeland Island.

The nest is usually a depression in the ground, which may or may not be lined with bits of grass or similar materials. The eggs are mottled and camouflaged. Both sexes share incubation duties. The young hatch after 22–27 days and fledge after 21–24 days.  If the parents are disturbed and flush from the nest frequently the incubation period could be extended to as long as 34 days.

When hatched, the chicks are downy. Neither altricial nor precocial, the chicks begin to move around and explore their surroundings within one to three days after hatching.  Usually, they do not stray far from the nest. Chicks are brooded by the adults for the first ten days after hatching.  Both parents care for hatchlings.  Chick diets always include fish, and parents selectively bring larger prey items to chicks than they eat themselves.  Males bring more food than females. Feeding by the parents lasts for roughly a month before being weaned off slowly.  After fledging, the juveniles learn to feed themselves, including the difficult method of plunge-diving.  They will fly south to winter with the help of their parents.

I hope you enjoyed this post.  Now I have a bit of bad news.   I was told yesterday that all the Terns had deserted the island and that was probably due to the 4 peregrines on the island. 

I am linking this post with Eileen's SATURDAYS CRITTERS.  

Thank you for visiting.

Many thanks for leaving comments on this post.