Arctic Sterna Paradisaea

The arctic tern known scientifically as the Sterna paradisaea it is a circumpolar seabird commonly recognised due to its strong migratory patterns. Having one of the largest migration patterns known throughout the animal kingdom traveling from its northern breeding grounds in arctic and sub-arctic regions spanning across Europe, Asia, Alaska and northern Canada. They migrate to Antarctic coast lines seeing two summers a year
Using the data from the Tracking of Arctic terns Sterna paradisaea reveals longest animal migration attaching in which miniature archival light loggers more commonly known as geolocators were attached to 11 arctic sterns allowing measurement of the amount of ambient sunlight levels over long periods of time. Light data could then be downloaded and interpreted through analysis of the data collected the arctic turn was said to make a journey of (59,000 to 81,600 km) from their northern homes to the Antarctic coasts.
During this journey there was common stopover point in the middle of the north Atlantic shown in figure 1. This provided opportunity to feed on zoo-plankton and small fish to provide energy for the trip ahead. The birds usually head along the coast of western Africa or western Europe the birds are then faced with a choice of staying on the coast of west
Africa of crossing the Atlantic form Cape Verde to continue their journey on the Brazilian coast an average of half birds being tracked decided to take the south American route this was explained to be a result of both routes having favourable wind for the turns.
When the northern winter months come to an end the terns begin their journey home from the Antarctic waters. Through new evidence and tracking it has been shown that on the arctic terns return journey they take a several thousand kilometre detour in the form of a large “S” shape pattern seen in figure 1. This creates more favourable winds by moving counter-clockwise in the southern hemisphere and clockwise in the northern creating a more energy efficient route and saving the arctic tern several thousand kilometres. Figure 1: demonstrating the arctic terns journey to the Antarctic in yellow and the return in the orange.
From- http://news.bbc.co.uk/2/hi/sci/tech/8451908.stm
The arctic tern presents many adaptations that allow it to endure its long migrations. Its wings have what is referred to as a “high aspect ratio” meaning the bird has long narrow wings making it more adapted for its long distance gliding and soaring. The bird is also an opportunistic feeder with primarily with small oceanic creatures such as fish and zooplankton as its main food source. This allows the bird to nourish itself whilst migrating across the Atlantic Ocean.
A mental adaptation demonstrated by the arctic turn is its “clock and compass” theory of navigation. The birds use their genetically imbedded sense of direction to find their desired southern direction the bird then uses the sun as a visual cue for inclination of heading southward. It has also demonstrated the ability to track the position of the sun and can use its position to measure the angles it’s traveling in. Allowing it to maintain the correct direction to the Antarctic.
Commonly Arctic terns use flyways defined as a flight path used in bird migration. Flyways generally span over continents and often oceans. Arctic terns have been known to use the Pacific flyway spanning from Alaska to Patagonia. When migrating from the breeding grounds to the Antarctic the arctic tern will follow the flyway until reaching South American coastline. As the arctic tern is a bird of both hemispheres it uses multiple flyways that can depend on where it breeding grounds are and what winds seem most favourable. It has been seen using the East Atlantic flyway, The West Asian- east African flyway and the Atlantic Americas flyway.

Arctic terns have demonstrated a high level of sensitivity towards human interference. Competition for food sources with fishermen can result in breeding failure and cause nest abandonment. Humans with dogs around nesting sites have been shown to prevent terns from occupying roasting sites and cause nest abandonment. In some cases of reindeer herding and helicopter landings caused complete abandonment of nest and roosting sites. The present threat of shooting, egging and trapping terns is present across breeding sites and migration routes. This may cause terns to abandon specific migration routes and large nest sites. Arctic terns also have a number of natural predators such as the arctic fox, Norway rats and gulls all shown to attack and eat terns and tern eggs. A major threat that may pose declination of arctic tern populous is the doubling of CO2 resulting in 20%-50% of vegetation type used by arctic terns to disappear which may pose abandonment of nesting sites and breeding failure. 12 Some methods of conservation are regular maintenance and measurement of nesting inventory and productivity, evaluating human disturbance at key nesting sites, create rat, gull and fox prevention programs, and protecting popular nesting sites.11

While there has been threat that there is a steady decline in arctic tern levels.
It has been stated that while there is a present decrease population. It is not a rapid or substantial enough to have overall impact on the estimated breeding pairs of arctic terns. This observation of decrease in popular size has not approached at a rapid enough rate to pose any threat of population size and further more does not approach any thresholds of vulnerability amongst the population. This puts the arctic tern at the least concern level of conservation. It has also been stated that due to the arctic terns secluded breeding sites and large distribution amongst the northern
hemisphere

Figure 2: showing the abundance of breeding pairs in the U.K in 1986-2012 demonstrating the steady decline. http://jncc.defra.gov.uk/page-2896

To conclude the arctic tern, Sterna paradisaea is a strongly migratory bird that makes one the largest recorded migration journeys traveling an average 44,000 km and seeing to summers a year. Using the clock and compass navigation method to guide it through its journey and its opportunistic feeding style and oceanic prey to nourish itself whilst making its large journey. The bird also makes use of its high wing aspect ratio to glide and soar for extremely long distances along the coasts of South America and east Africa. Despite the birds difficult to evaluate numbers it is listed as a least concerned level of threat. However their still present threat of competition of fishermen for food, competition with gulls and doubling of CO2 levels in the atmosphere. 1,2,3,4,5,6,7,8,9,10,11,12