0 the arctic tern (sterna paradisaea) is a seabird of the tern family sternidae .
1  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) .
2  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 for the southern summer and back again about six months later .
3  recent studies have shown average annual roundtrip lengths of about 70,900 km (44,100 mi) for birds nesting in iceland and greenland and c .
4  90,000 km (56,000 mi) for birds nesting in the netherlands .
5  these are by far the longest migrations known in the animal kingdom .
6  the arctic tern flies as well as glides through the air , performing almost all of its tasks in the air .
7  it nests once every one to three years (depending on its mating cycle); once it has finished nesting it takes to the sky for another long southern migration .
8 arctic terns are medium-sized birds .
9  they have a length of 2839 cm (1115 in) and a wingspan of 6575 cm (2630 in) .
10  they are mainly grey and white plumaged , with a red/orangish beak and feet , white forehead , a black nape and crown (streaked white), and white cheeks .
11  the grey mantle is 305 mm , and the scapulae are fringed brown , some tipped white .
12  the upper wing is grey with a white leading edge , and the collar is completely white , as is the rump .
13  the deeply forked tail is whitish , with grey outer webs .
14 arctic terns are long-lived birds , with many reaching fifteen to thirty years of age .
15  they eat mainly fish and small marine invertebrates .
16  the species is abundant , with an estimated one million individuals .
17  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 .
18 the arctic tern was known as sea swallow describing their slender shape as they swoop over the water .
19 the arctic tern has a continuous worldwide circumpolar breeding distribution; there are no recognized subspecies .
20  it can be found in coastal regions in cooler temperate parts of north america and eurasia during the northern summer .
21  while wintering during the southern summer , it can be found at sea , reaching the northern edge of the antarctic ice .
22 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 19,000 km (12,000 mi) .
23  the long journey ensures that this bird sees two summers per year and more daylight than any other creature on the planet .
24  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 .
25  assuming a direct route of flight , the distance covered would have been more than 22,000 km (14,000 mi) .
26  another example is that of a chick ringed in labrador , canada , on 23 july 1928. it was found in south africa four months later .
27 a 2010 study using tracking devices attached to the birds showed that the above examples are not unusual for the species .
28  in fact , it turned out , previous research had seriously underestimated the annual distances travelled by the arctic tern .
29  eleven birds that bred in greenland or iceland covered 70,900 km (44,100 mi) on average in a year , with a maximum of 81,600 km (50,700 mi) .
30  the difference from previous estimates is due to the birds' taking meandering courses rather than following a straight route as was previously assumed .
31  the birds follow a somewhat convoluted course in order to take advantage of prevailing winds .
32  the average arctic tern lives about thirty years , and will , based on the above research , travel some 2.4 million km (1.5 million mi) during its lifetime , the equivalent of a roundtrip from earth to the moon over 3 times .
33 a 2013 tracking study of half a dozen arctic terns breeding in the netherlands shows average annual migrations of c .
34  90,000 km (56,000 mi) .
35  on their way south , these birds roughly followed the coastlines of europe and africa .
36  having rounded the southern tip of africa , they then turned east , some flying approximately halfway to australia before again turning south to eventually reach wilkes land in the north-eastern antarctic .
37  one bird flew several hundred kilometres along the south coast of australia before turning south for the antarctic , while one flew along the entire south coast of australia , passing between australia and tasmania .
38  having reached the melbourne area , it turned south and flew in an arc to wilkes land in the north-east antarctic , passing the south-western tip of new zealand's south island en route .
39  once back in the netherlands , this bird had journeyed c .
40  91,000 km (57,000 mi), the longest migration yet recorded for any animal .
41 arctic terns usually migrate sufficiently far offshore that they are rarely seen from land outside the breeding season .
42 the arctic tern is a medium-sized bird around 3336 cm (1314 in) from the tip of its beak to the tip of its tail .
43  the wingspan is 7685 cm (3033 in) .
44  the weight is 86127 g (3.04.5 oz) .
45  the beak is dark red , as are the short legs and webbed feet .
46  like most terns , the arctic tern has high aspect ratio wings and a tail with a deep fork .
47 the adult plumage is grey above , with a black nape and crown and white cheeks .
48  the upperwings are pale grey , with the area near the wingtip being translucent .
49  the tail is white , and the underparts pale grey .
50  both sexes are similar in appearance .
51  the winter plumage is similar , but the crown is whiter and the bills are darker .
52 an arctic tern in flight with wings spreadjuveniles differ from adults in their black bill and legs , "scaly" appearing wings , and mantle with dark feather tips , dark carpal wing bar , and short tail streamers .
53  during their first summer , juveniles also have a whiter forecrown .
54 the species has a variety of calls; the two most common being the alarm call , made when possible predators (such as humans or other mammals) enter the colonies , and the advertising call .
55  the advertising call is social in nature , made when returning to the colony and during aggressive encounters between individuals .
56  it is unique to each individual tern and as such it serves a similar role to the bird song of passerines , identifying individuals .
57  eight other calls have been described , from begging calls made by females during mating to attack calls made while swooping at intruders .
58 while the arctic tern is similar to the common and roseate terns , its colouring , profile , and call are slightly different .
59  compared to the common tern , it has a longer tail and mono-coloured bill , while the main differences from the roseate are its slightly darker colour and longer wings .
60  the arctic tern's call is more nasal and rasping than that of the common , and is easily distinguishable from that of the roseate .
61 this bird's closest relatives are a group of south polar species , the south american (sterna hirundinacea), kerguelen (s .
62  virgata), and antarctic (s .
63  vittata) terns .
64  on the wintering grounds , the arctic tern can be distinguished from these relatives; the six-month difference in moult is the best clue here , with arctic terns being in winter plumage during the southern summer .
65  the southern species also do not show darker wingtips in flight .
66 the immature plumages of arctic tern were originally described as separate species , sterna portlandica and sterna pikei .
67 breeding begins around the third or fourth year .
68  arctic terns mate for life , and in most cases , return to the same colony each year .
69  courtship is elaborate , especially in birds nesting for the first time .
70  courtship begins with a so-called "high flight", where a female will chase the male to a high altitude and then slowly descend .
71  this display is followed by "fish flights", where the male will offer fish to the female .
72  courtship on the ground involves strutting with a raised tail and lowered wings .
73  after this , both birds will usually fly and circle each other .
74 both sexes agree on a site for a nest , and both will defend the site .
75  during this time , the male continues to feed the female .
76  mating occurs shortly after this .
77  breeding takes place in colonies on coasts , islands and occasionally inland on tundra near water .
78  it often forms mixed flocks with the common tern .
79  it lays from one to three eggs per clutch , most often two .
80 it is one of the most aggressive terns , fiercely defensive of its nest and young .
81  it will attack humans and large predators , usually striking the top or back of the head .
82  although it is too small to cause serious injury , it is still capable of drawing blood .
83  other birds can benefit from nesting in an area defended by arctic terns .
84 the nest is usually a depression in the ground , which may or may not be lined with bits of grass or similar materials .
85  the eggs are mottled and camouflaged .
86  both sexes share incubation duties .
87  the young hatch after 2227 days and fledge after 2124 days .
88  if the parents are disturbed and flush from the nest frequently the incubation period could be extended to as long as 34 days .
89 when hatched , the chicks are downy .
90  neither altricial nor precocial , the chicks begin to move around and explore their surroundings within one to three days after hatching .
91  usually , they do not stray far from the nest .
92  chicks are brooded by the adults for the first ten days after hatching .
93  both parents care for hatchlings .
94  chick diets always include fish , and parents selectively bring larger prey items to chicks than they eat themselves .
95  males bring more food than females .
96  feeding by the parents lasts for roughly a month before being weaned off slowly .
97  after fledging , the juveniles learn to feed themselves , including the difficult method of plunge-diving .
98  they will fly south to winter with the help of their parents .
99 arctic terns are long-lived birds that spend considerable time raising only a few young , and are thus said to be k-selected .
100  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% .
101 the diet of the arctic tern varies depending on location and time , but is usually carnivorous .
102  in most cases , it eats small fish or marine crustaceans .
103  fish species comprise the most important part of the diet , and account for more of the biomass consumed than any other food .
104  prey species are immature (12 year old) shoaling species such as herring , cod , sandlances , and capelin .
105  among the marine crustaceans eaten are amphipods , crabs and krill .
106  sometimes , these birds also eat molluscs , marine worms , or berries , and on their northern breeding grounds , insects .
107 arctic terns sometimes dip down to the surface of the water to catch prey close to the surface .
108  they may also chase insects in the air when breeding .
109  it is also thought that arctic terns may , in spite of their small size , occasionally engage in kleptoparasitism by swooping at birds so as to startle them into releasing their catches .
110  several species are targetedconspecifics , other terns (like the common tern), and some auk and grebe species .
111 while nesting , arctic terns are vulnerable to predation by cats and other animals .
112  besides being a competitor for nesting sites , the larger herring gull steals eggs and hatchlings .
113  camouflaged eggs help prevent this , as do isolated nesting sites .
114  while feeding , skuas , gulls , and other tern species will often harass the birds and steal their food .
115  they often form mixed colonies with other terns , such as common and sandwich terns .
116 arctic terns are considered threatened or species of concern in certain states .
117  they are also among a species to which the agreement on the conservation of african-eurasian migratory waterbirds applies .
118  the species reduced population in new england in the late nineteenth-century because of hunting for the millinery trade .
119  exploitation continues today in western greenland , where the species has reduced population greatly since 1950.at the southern part of their range , the arctic tern has been reducing in numbers .
120  much of this is due to lack of food .
121  however , most of these birds' range is extremely remote , with no apparent trend in the species as a whole .
122 "birdlife international has considered the species to be at lower risk since 1988, believing that there are approximately one million individuals around the world" .
