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Antarctica is a continent devoid of human settlement, except for the over 50 research stations built there by 27 different countries. But the Arctic region is home to more than 4 million people, many of which are indigenous people, native to the area

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Making a round trip of up to 90 000km a year while weighing about the same as a quarter pound burger and seeing more continuous daylight than any other animal on earth in the north and south polar summers makes this elegant extreme flier one of the most remarkable of all birds.

arctic tern facts Basics

Average Weight: 95 to 120g (3.3 - 4.2 oz),

Average Length: 33 to 39 cm long (13 - 15.5 inches), wingspan 66 - 77 cm (26 - 30 inches).

Breeding Season: April/May in the Arctic summer, when the young have fledged and become independent, they then fly to Antarctica (including the juveniles) where they winter during the Antarctic summer before flying back again to the Arctic to breed the following year.

Estimated world population: 2 million individuals, 500-900,000 breeding pairs in Europe.

Feeding: Opportunistic feeders, they feed on fish and larger zooplankton such as krill especially when in Antarctica. They catch their prey by seeing them from the air, searching and hovering much like a hawk does on the land and then diving to catch them.

Conservation status: Conservation status - a conservation priority in some parts of the range.

Distribution: Circumpolar around the Arctic including many islands, native to the far north usually found in treeless tundra.

Predators: Nests are vulnerable as they are generally on the ground, arctic foxes, polar bears and mink may take eggs and chicks.

picture courtesy
Distribution range of the Arctic Tern, nesting region in red
Andreas Trepte - licensed under CC BY-SA 2.5

What are Arctic Terns like? how do they survive?

The Arctic Tern is a member of a very exclusive animal club, it can be found at different times at both poles. The polar regions are areas of very high seasonal productivity. Very long day length with up to 24 hours daylight in the summer depending on the distance to the pole. This means that photosynthetic productivity (plant growth) is in overdrive, especially in the sea which leads to an abundance of other potential food a little further along the food chain which is then available to larger animals such as birds like terns.

Such is this abundance of seasonal food, it is actually worth the effort for terns to fly the length of the planet to take advantage of the Antarctic summer after spending the Arctic summer having partaken of its own seasonal abundance. They breed in the Arctic and use Antarctica as the wintering grounds (though it is the Antarctic summer!).

The flying abilities of Arctic terns are amongst the most astonishing of any birds. They have a length of a little over 30cm (a foot), a wingspan of less than a meter (about two and a half feet) and a weight of around 100g (3.5oz, or a little less than a quarterpounder burger). Despite this, they have been measured at flying up 90,000 km (nearly 56,000 miles) a year. This has recently be proven by attaching trackers onto birds and is around twice the previously thought distance. The reason is that the birds follow the prevailing wind patterns that carry them along rather than taking the most direct routes.

They stop over in an area of upwelling and high productivity in the North-Atlantic for around 25 days when flying south. It takes them about 3 months on the journey south, but only around 40 days to fly back north again, mainly due to the strength of the prevailing winds.

They arrive in the north in April/May, mate, nest and rear their young. They leave again in July/August to reach Antarctica in November where they stay until February/March. Both the Arctic and the Antarctic have 24 hours daylight in mid-summer and Arctic Terns are in both places in mid summer. They are most probably the animal that experiences the most daylight of any on the planet.

Arctic terns have a very particular and extreme lifestyle, all the more surprising when you realise how small they are, they have a number of anatomical, behavioural and physiological adaptations that allow them to survive successfully.
Arctic Tern Adaptations:

Very high metabolic rate (physiological) - Many polar and cold climate birds deal with cold temperatures by consuming and burning food to generate heat from within. In order to do this they have to consume high energy food that is easily and quickly digestible. The fish and oily krill and other prey that terns feed on provide the readily accessible fuel that enables them to live their fast-paced life.

Dive bomb other animals that approach the nest, aiming at the head (behavioural) - Whether a potential predator or just some big clumsy animal that might trample the nest, eggs and chicks, they all come in for the same treatment. Arctic terns dive repeatedly at any animal (including man) that they think represents a threat. They call out in alarm and repeatedly attack from behind the head so they have maximum disorientation effect and are less likely to be harmed themselves. They keep going as long as they feel threatened and stop when the threat is sufficiently far away. Often you will have no idea where the nest actually is other than somewhere near where you were. A frantic term attack can leave even a polar bear with bloody wounds to the head!

Nests in colonies with other birds (behavioural) - This maximizes the effectiveness of the defensive dive-bombing behaviour with many birds involved at the same time.

Flies from the Arctic to Antarctic and back again every year (behavioural) - Arctic Terns nest in the Arctic during the summer, when their young have fledged and become independent, they then fly to Antarctica (including the juveniles) where they winter during the Antarctic summer before flying back again to the Arctic to breed the following year. They do this to take advantage of food abundances at the peak times of year and to avoid food shortages at other times. They nest and rear their young all around the Arctic, though mainly fly south along an Atlantic route before spreading out again once in Antarctica.

Fantastic fliers - as you might imagine (anatomical and physiological) - Shaped with tail feathers that can be spread wide or pulled into a narrow dart to change aerodynamics in flight for covering distance or hovering and diving while feeding. Hollow bones for lightness. Able to sleep on the wing during migrations. Short legs that aid an aerodynamic shape in the air but make the birds rather clumsy on the ground.

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Arctic Tern Facts and Adaptations - Sterna paradisaea

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Making a round trip of up to 90 000km a year while weighing about the same as a quarter pound burger and seeing more continuous daylight than any other animal on earth in the north and south polar summers makes this elegant extreme flier one of the most remarkable of all birds.

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Terrestrial Invertebrates in Antarctica - Cold Acclimation and Acclimatization

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They may be small and hard to find, but terrestrial invertebrates in Antarctica are amongst the hardiest of its citizens living in the harshest environments, places where as recently as 30 years ago it was thought that nothing could live. Inevitably to find terrestrial Antarctic invertebrates, you have to go looking for them.

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South Polar Skua - Antarctica fact file birds

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More often though the first sign that a visitor gets of being near to a skuas nest or chick is of a sudden heart-stopping sound just behind your head caused by the rush of air through the wing feathers of the parent bird flying at speed past your head from behind, much too close for comfort.

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Snow petrels are pure white birds with jet black beaks and eyes. They are the size of a pigeon and arguably the most beautiful of all the Antarctic birds.

Snow Petrel Basics

Weight: 240 to 460g, it is a characteristic of snow petrels that there can be a large range of sizes amongst individuals. 30 - 40 cm, wingspan: 75 - 95 cm

Breeding Season: Nests are made and eggs laid from October to November, the chicks fledge and leave the nest 41 - 45 days later, snow petrels can live for up to 20 years.

Estimated world population: - More than 4,000,000 individuals.

Feeding: A varied seafood diet of krill, fish and squid that are usually taken very close to the surface, though shallow dives are also undertaken. They will also feed on carrion where it is available.

Conservation status: Least concern.

Distribution: Circumpolar, usually found near to pack ice and even continuous ice as long as there are open water leads to feed at. Breeds mainly on the Antarctic continent and surrounding islands, it is the most southerly breeding bird species, breeding even further south than the Emperor penguin. Snow petrel have even been seen at the south pole.

Predators: Antarctic (south polar) skuas, though weather conditions especially snow blocking nesting sites cause much greater loss of eggs and chicks.

What are snow petrels like?

In their appearance and behaviour snow petrels symbolize the very essence of the deep south. They are the purest of white and despite their diminutive size are as tough as animal needs to be to survive and even thrive in low temperatures and with a frequently high wind chill. They are frequently encountered in their hundreds, rarely in thousands, they tend to be spread out over a wide nesting area rather than being close together in large discrete colonies as are other Antarctic species.

They feed largely on krill and must always be near to the sea in order to feed. They are found therefore particularly along coasts and along the Antarctic peninsula.

The flying pair of birds in the picture are are a courting couple. In the Antarctic spring the males go looking for mates, and the females put them through their paces to assess their suitability and tenacity.

The courtship ritual consists initially of a male snow petrel following a female as she flies around the nesting area which is frequently a rocky outcrop or cliff with suitable ledges or nest holes. The female then leads him around the cliffs in a high speed aerial ballet, climbing and diving, flying almost into the cliff face at full speed before changing direction with an imperceptible twist of the wing at the last moment.

The poor beleaguered male not only has to match this aeronautical master class, but he has to do it as close as possible to the female and without a script, gauging her every move while proving himself her equal at rapid flying. Many would be suitors seem to give up and get left behind, certainly in the early days. In this picture the male is calling to the female during a relatively relaxed moment.

Photographing flying snow petrels requires a lens on fixed focus, bright light, fast shutter, small aperture, and much cursing. Even then, it all happens so quickly that you don't really know what you've got until you can look at the picture on a bigger screen.

Why are these snow petrels hiding down a hole?

Unusually for Antarctic birds, snow petrels seem to apply some thought to the practicalities of a nest site. This pair are at the entrance to their nest which has been made in a natural crevice amongst some large broken-up rocks. This is a frequent choice for a nest site though not always available or in plentiful supply as snow petrels nest very far south and such crevices are frequently snowed or iced up.

Attempting to approach a nest (as I did on many occasions when helping in a long term programme on nesting success) brings out the worst in snow petrels. A well aimed stream of foul smelling, bright pink, oily, semi-digested krill mixed with oily stomach secretions would come in your direction as their (admirably unpleasant) defence mechanism. As small birds, nesting in crevices gets them out of the wind so reducing their risk of chilling in the wind and also protects them from nest raiding birds such as skuas. Antarctic has no land based nest raiding mammals such as cats or rats.

Snow petrels have been known to nest far inland on the Antarctic continent, 325 km. from the nearest sea that they must travel to in order to feed. They must nest on rock and in these cases choose "nunataks" isolated outcrops of tall rock ridges and mountains that protrude above the surrounding ice from the bed rock.

Isn't it cold and windy sitting out on the sea ice?

Snow petrels are birds of the Antarctic, they don't migrate as such but move further north in winter as the cold weather sets in. Research in recent years has shown that the Antarctic ocean beneath the winter ice is surprisingly rich in life - a fact that it seems these birds have known about for some time.

They frequently arrive surprisingly far south in the winter in ridiculously low temperatures and high winds for such small creatures and rest overnight on totally exposed sea-ice, as here. Any spring and summer shelter is blocked up by now by blown snow. The reason they venture south in such adverse conditions would seem to be in order to take advantage of the abundance beneath the ice and the relative rarity of summer competitors.

Why are these snow petrels hanging around the edge of this tide crack?

That these birds are prepared to undergo so much to find their food is testament to the nutritional value of that food - krill. Here snow petrels (and in the first photograph a crabeater seal too) are taking advantage of a tide crack to fish through in the case of the birds and to breathe at in the case of the seal who will be busy fishing for krill under the ice. A tide crack is a long narrow open lead of water that stretches between two points such as nearby islands or exposed rocks. It arises when the tide rises and falls, when the tide rises the crack opens when it falls, the crack closes. Such tide cracks can easily stretch for several kilometres, but never being more than about 50cm wide.

The snow petrels space themselves out along the tide crack and sit patiently waiting for a krill to swim by at which point they jump out and hover just above the surface to take the tasty morsel.

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Snow petrels - Antarctica fact file, birds

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Snow petrels are pure white birds with jet black beaks and eyes. They are the size of a pigeon and arguably the most beautiful of all the Antarctic birds. Snow Petrel Basics Weight: 240 to 460g, it is a characteristic of snow petrels that there can be a large range of sizes amongst individuals.

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"The bird which made the breeze to blow" has the longest wingspan of any bird on the planet, wandering albatrosses live up to their name on long fishing trips of 10-20 days when they can cover 10,000 km using barely more energy than when they are sitting on the nest.

wandering albatross facts - Basics

Average Weight: 5.9 to 12.7 kg, commonly 6.4 - 11.9 kg, males are typically around 20% heavier than females. Immature birds have been reported at up to 16.1 kg shortly after leaving the nest due to still having fat reserves that sustained while on the nest waiting for the adults to return. More typically fledgling albatrosses are 1-2 kg heavier than the adult birds. 107 - 135 cm

Wingspan: average 3.1 m (10 ft 2 inches) and up to 3.5 m, these famously have the largest wingspan of any bird, larger but unverified sizes have been reported.

Breeding Season: An unusual breeding system whereby one chick is produced every two years by pair of adults that mate for life, though around a third of pairs defer breeding beyond the one year gap. Adults return to colonies which are on sub-Antarctic islands amongst open vegetation on exposed ridges or small hills in November, eggs are laid in December and January on a nest that is a mound of vegetation held together with mud and hatch 11 weeks later.

Estimated world population: - 26,000.

Feeding & diet: The mainstay of the albatross diet is fish, squid and crustaceans which are caught at night at the sea surface or in shallow dives. They will also follow boats and ships of any type for discarded food especially fishing boats where fish offal from gutted and filleted fish may be thrown overboard.

Conservation status: Vulnerable, many populations are in a long term decline as a result of losses from longline fisheries, the slow breeding rate of these long lived birds means they are slow to recover.

Distribution: Circumpolar, usually stays in the sub-Antarctic region not venturing further south than about 60° S. 75% of the world breeding population is found in three places, South Georgia (25%), Prince Edwards Islands (40%), Crozet and Kerguelan Islands (10%). Non-breeding birds and juveniles usually spend their time north of 50° S, between there and the sub-tropics.

What are Wandering Albatrosses like?

The wandering albatross is a truly remarkable bird. South Georgia residents of the species have been known to make regular fishing trips that take them as far as the seas off Uruguay and southern Brazil. Round trips of thousands of kilometres over several days repeated frequently, and all to catch food for themselves and their young, these are birds that will fly 1,000 km for breakfast. Any visiting ship to the South Atlantic will almost certainly at some time be followed by one or more albatrosses, wheeling and turning around the ship, following at a distance hypnotically and silently.

The bird in the picture to the right is a relative juvenile recognisable by the dark wing tips. As the bird ages, the dark patches recede further to the tips of the wings, so it becomes whiter. After leaving the nest they don't return again for 5 to 7 years when they return to the island where they were born. Albatrosses mate for life and can live to be over 60 years old probably making them the animal that travels further than any other in their life-time.

The albatross is a large bird with a large chick. The chick is so large (12kg when it leaves the nest) that it takes just over 12 months to develop fully. This means that the albatross is in the same select group as king and emperor penguins in that it has a breeding cycle that stretches over 2 years.

What sort of fliers are Wandering Albatrosses?

The birds rarely flap their wings that can measure up to 3.5 metres in span. They are gliding birds that swoop low over the never ending swell of the southern ocean, using the energy of the wind to gain height and then the potential energy of the height to glide down again and gain distance in a process known as "dynamic soaring" that allows them to fly into the wind using the energy of the wind itself. They are able to fly continuously and cover vast distances with the minimum of effort, 950 km per day at an average speed of 40 kmh for days or weeks on end is a typical trip average. One bird was tracked circling Antarctica in 46 days

There is a mechanism within the base of the wing to "lock" it in an extended position so the bird doesn't need to strain to keep its "arms" out. Albatrosses have many more "slow twitch" fibers in their flight muscles than do other birds which do the job of making continuous small adjustments to the wing during gliding flight rather than having fast twitch fibers for flapping flight. Albatross flight is achieved from a combination of the winds that blow around the southern ocean, those long thin high "aspect ratio" wings, an assemblage of muscles for constant fine tuning of the three dimensional attitude of the wings and an on board bird brain that controls those muscles while also being prepared to set out on journeys of a week or two that cover more distance than most birds in a year.

They may also use rising waves to gather energy to lift them into the air, the wave rises and pushes air with it which in turns lifts the albatross. Studies have shown that albatrosses flying in favourable winds use only a little more energy than they do when resting on land (Sachs et. al 2012)

Foraging paths of 40 incubating wandering albatrosses from Possession Island, Crozet archipelago (white square) in January - March 2011 measured by attaching 20g (0.2% of the birds weight) GPS trackers to the birds. The trips varied in length from 3.6 to 21.1 days and from 475 to 4,507 km. Grémillet et al. 2012.

The down side of those wings and flight muscles is that taking off can be problematic, albatrosses favour windswept rises on which to build their nests which makes take off into the wind much easier. Real difficulties come when they are taking off from the surface of the sea in calm conditions, long runs are sometimes required to get up enough speed and enough air under those wings, the bird in the picture is shown doing such a thing. The reason for the difficult take off may be that the bird has gorged itself on too much food, especially if it has been feeding on carrion floating on the sea surface, in such conditions vomiting to lighten the load helps with take off again, wandering albatrosses can consume up to 3 kg of food at a single sitting, about 25% of their body mass. They do however often remain at the sea surface for several hours after a large meal while digestion takes place. Wandering albatrosses have very acidic stomachs, more so than other seabirds and similar to carrion feeding vultures, this allows the birds to digest the food they find quickly, useful for a flying bird and also when feeding on carrion and fishery wastes from fishing boats.

In folklore the bird carries the soul of dead mariners. If a sailor kills the bird, bad luck would fall upon him for the rest of his natural life. This was not a universal belief as the feet of the albatross were once used as tobacco pouches and the long hollow wing bones for the stems of pipes.

In what way are Wandering Albatrosses threatened?

Wandering albatrosses are the largest species of the group of albatrosses which comprises 22 species, of those 22 species, 15 are considered to be threatened with extinction and the other 7 "near threatened", of the 15, 3 species are "critically endangered". Populations have monitored since the 1960's and are in decline in many areas. They are all long lived species which begin breeding quite late in life (7 - 10 year old) and breed at a slow rate with a pair producing one fledged chick every 2 or 3 years. Small increases in the death rate can therefore have a serious effect on albatross populations. Currently about 100,000 albatrosses a year are being killed many of them accidentally by largely illegal long line fishing.

The main hazard is from long line fishing, this is a method where long fishing lines are laid out at sea by boats, at intervals along the main line, there are shorter side-lines which terminate in a baited hook. The long line can carry hundreds or even thousands of hooks. It is laid out in the water column or to sink to the sea floor, left for a while and then pulled back up again. In itself it is a controversial technique in that it is indiscriminate and can catch and kill marine life that is not intended. The danger for albatrosses is when the lines are being set, they are set out from the back of the boat and for a while are visible at or just beneath the surface, the albatrosses at this point come down attracted by the bait and become hooked, the descending line then drags them down beneath the water where they drown. Legal commercial fisheries are taking steps to combat these deaths such as by weighting the lines so they sink quickly while being set, by flying long streamers behind the boats while setting lines to deter the birds from coming close or by setting lines at night or from beneath the surface of the water.

A continuing problem however is from illegal fisheries especially for the Patagonian Toothfish Dissostichus antarcticus sold commercial as Chilean Sea Bass or under a number of other names in high end restaurants, such boats are breaking the law by fishing in the first place and don't take any measures to avoid albatross deaths. These are thought to be responsible for the majority of albatross deaths.

Other threats are collisions during flight with taught trawler cables which can break the birds wings.

The answer is difficult as most of these deaths take place in the open ocean either not under the jurisdiction of any one country or of the waters of various countries meaning that international co-operation is needed to help conserve these iconic and magnificent birds.

Protect the Wandering Albatross. albatross are facing a decline due to illegal and unregulated longline fishing. Populations of Wandering Albatross are declining at an estimated 1% per year, exposing them to probable extinction within the century if nothing is done to protect them.

"The bird that made the breeze to blow" - Samuel Taylor Coleridge from"The Rime of the Ancient Mariner".

Copyright picture used by permission: Wandering Albatross flying over the South Atlantic and Wandering Albatross taking off - Liam Quinn from Canada, used under Creative Commons 2.0 Attribution Share and Share Alike generic license. / Albatross and line - NOAA.

References:
David Grémillet Aurélien Prudor, Yvon le Maho, Henri Weimerskirch, 2012, Vultures of the Seas: Hyperacidic Stomachs in Wandering Albatrosses as an Adaptation to Dispersed Food Resources, including Fishery Wastes. PLOS ONE

Gottfried Sachs, Johannes Traugott, Anna P. Nesterova, Giacomo Dell'Omo, Franz Kümmeth, Wolfgang Heidrich, Alexei L. Vyssotsk, Francesco Bonadonna, 2012. Flying at No Mechanical Energy Cost: Disclosing the Secret of Wandering Albatrosses. PLOS ONE

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Wandering Alabatross - Antarctica fact file birds

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"The bird which made the breeze to blow" has the longest wingspan of any bird on the planet, wandering albatrosses live up to their name on long fishing trips of 10-20 days when they can cover 10,000 km using barely more energy than when they are sitting on the nest.

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Anatarctica gallery weddell seal, mother and pup

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Weddell seals are animals of the ice. They live further south than any other mammal. Between the end of August and early November in the southern hemisphere spring, the females haul themselves out of holes in the ice and give birth to their pups.

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Krill is a Norwegian word for "whale food", more than anything else, krill are the engine that powers the Antarctic ecosystem. Krill adaptations

Krill are a small semi-transparent crustacean like a shrimp, about 6 cm (over 2") in length and a gram in weight when fully grown, they can live for up to 7 years which is quite remarkable considering the wide variety of animals that feed on them in huge quantities. Krill belong to the animals that make up the zooplankton. The "zoo" means that they are animals, the "plankton" means that they float in the upper reaches of the water column and are at the mercy of the ocean currents, being able to change their position in the water column, but not able to swim against the current or migrate in the normal sense.

Krill feed on microscopic phytoplankton ("phyto" - plant) that are extremely abundant in Antarctic waters due to the great upwellings of deep waters at the Antarctic convergence. These upwellings bring with them great amounts of dissolved nutrients, especially nitrate and phosphate that fertilize the microscopic but hugely abundant phytoplankton in the same way that a farmer puts fertiliser on the fields. Add to this the 24 hour sunlight of the summer months and the scene is set for a super-abundance of life despite the ocean temperature being just a couple of degrees above freezing point.

Krill are unusual in that they are so super-abundant and relatively large when compared to other phytoplankton feeders in other oceans. This means that many large animals such as seals, penguins, whales and myriad other birds are able to tap the food chain close to the producers (phytoplankton) before energy is lost in intermediate stages, so the Antarctic supports a large population of large animals.

Krill they drift around in swarms that are so large it is difficult to imagine. They are usually either not in a particular area at all or are present in huge quantities. Swarms estimated at containing 2 million tons of krill spreading over more than 450 square kilometres have been observed. This is the equivalent of 28.5 million human beings, 4 times the population of Greater London or approximately the entire population of Canada, averaging 70kg each, in area a third that of Greater London, so 12 times the human biomass density of London. The krill population of the world has been estimated at outweighing the human population, about half of this population is eaten each year by whales, penguins, seals, fish and pretty much every other Antarctic animal that is larger than them. They are then replaced by reproduction and growth.

There is a very complex ecology that has arisen involving krill and krill predators, with different species of predator feeding at different times of year at different depths and on different sizes and therefore age groups of krill. Despite the apparent ever present seemingly overwhelming presence of predators, krill can manage a lifespan of up to seven years, some of them at least.

Krill rise and fall in the water column depending on the time of day. They generally rise to feed in the night-time hours which may be darkness or at least a little less light intensity in mid summer with 24 hour daylight. During the day, they fall back into deeper water again (a few hundred meters) by "parachuting", holding their appendages out and slowly falling.

There have been attempts to catch krill commercially and great factory ships have been sent down to the Antarctic by some nations to catch and can krill quickly. Fortunately for the krill and the Antarctic ecosystem , krill go off very quickly after being caught, the Antarctic is a long way away and consumer interest remains fairly low (krill aren't very nice for people to eat). Krill is harvested by the Norwegians with smaller amounts by Japan, Russia and other nations. Around 210,000 tonnes per annum as of 2011 is harvested. Krill is used mainly in aquaculture and aquarium feeds (as fish food) and also in the pharmaceutical and health foods industry.

The most effective way of catching krill so far devised are the great baleen plates of baleen whales, such as Blue, Right, and Fin whales. These baleen plates were the original "whalebone" (actually not bone at all but keratin, the same stuff that hair, fingernails, hooves and rhinoceros horns are made from) hanging in two rows from the roof of the baleen whales mouth. The whale skull has an upper jaw that is a long straight structure sticking straight out from the "brain case" up to 10-12ft (3-3.5m) or more long in right whales. The baleen plates make a sort of triangular "tent" the floor of the tent is the lower jaw and the large tongue is inside (the tongue of a large blue whale can weigh as much as an adult bull elephant). The baleen whale takes a large mouthful of sea water and krill with its mouth open, it closes its mouth and then forces excess water out with its tongue. The baleen plates are filters that let out water and small plankton but retain the larger plankton such as krill which are then swallowed.

Different whales feed at different depths and their filters are arranged slightly differently so they do not all compete for the same sized krill.

One feeding technique of some larger baleen whales is "bubble netting". The whale, or sometimes two working in a pair, dive down below a dispersed krill swarm. They then swim upwards in a spiral blowing air bubbles as they go. The bubbles cause the krill to panic and swim inwards so concentrating them into a smaller space. The whale then swims directly up through the middle with mouth wide open taking in a huge mouthful of krill and water that the baleen plates then filter.

Feeding

One reason for the success and great abundance of krill is that they are very efficient feeders. Their filtration apparatus consists of fine hair-like structures called setae, which them selves have smaller setae coming off them. These can be seen in the electron micrograph to the right. The small pink object caught in the finer setae is about 1 micrometer across, the size of a bacterium, this is as small an object as any filter feeder in the oceans is able to capture and far smaller than the majority can mange. Compare this 1 micrometer object to the size of the phytoplankton in the image of typical phytoplankton at the bottom of this page. The total area of setae that an individual krill has is about 7500 times larger than shown in this picture.

Usually in pictures of krill, it is possible to see a green area just behind the head of captured phytoplankton, yet to be digested.

In the winter months krill feed under seasonal sea ice. Somewhat surprisingly, the underside of sea ice is often quite strongly coloured green/brown due to the phytoplankton that grow there despite the relatively low levels of light that are able to penetrate. Krill use the ends of their feeding appendages that have scraping setae rather than net-like setae to scrape off and eat the phytoplankton from the ice.

Krill and other Euphausids have a somewhat unusual ability amongst animals with exoskeletons in that they are able to shrink at a moult rather than grow if the food supply is very low for a extended time as it may well be in the Antarctic winter> this can happen after as little as seven days starvation and is thought to be an important method by which krill survive the seasonal fluctuations of food in Antarctica while being able to quickly feed and grow again when the seasonal abundance of phytoplankton arrives.

How Many Krill?

Estimates of krill are difficult to make, krill research is ongoing and moves quite slowly as krill are difficult to study effectively. They are small delicate animals easily damaged by nets, swarms can be widely dispersed and they may be anywhere in the water column down to around 400m depth depending on the time of day. To study krill, you need ocean going vessels able to work in and amongst ice and sophisticated fishing and sonar equipment. Recent studies have indicated that rather than all krill around Antarctica being essentially the same, they may well be composed of a number of separate and distinct populations, this means that they cannot be considered as a single entity when considering fisheries limits or investigating other ecosystem dynamics.
Current best estimates over the period of 1926-2004 give the following statistics:

Summer distribution range of around 19 million square kilometres.

Total number of krill in the region of 8 x 10 individuals, that's an 8 followed by 14 zeros, 800,000,000,000,000 or 114,000 each for every one of the 7 billion people on earth.

Krill standing biomass of 379 million tonnes.

The production of krill is in the range of 342 to 536 million tonnes per year, this is the amount that is available to predators and is the result of growth and reproduction and explains the apparent anomaly whereby more krill are consumed per year than the standing biomass.

Some studies have indicated (2004) that stocks of krill in Antarctica may have declined in recent years at least in some areas. The reason for this is likely to be a fall in the amount of sea ice in the winter months particularly in the Antarctic Peninsula region. The decline in krill may in turn account for the decline in the numbers of some penguin species.

Dr. Angus Atkinson from British Antarctic Survey:

"This is the first time that we have understood the full scale of this decline. Krill feed on the algae found under the surface of the sea-ice, which acts as a kind of nursery.

The Antarctic Peninsula, a key breeding ground for the krill, is one of the places in the world where there has been the greatest rise in temperatures due to global warming. This region has warmed by 2.5°C in the last 50 years (much more than the mean global rate), with a striking consequential decrease in winter sea-ice cover.

We don't fully understand how the loss of sea-ice here is connected to the warming, but we believe that it could be behind the decline in krill."

There are commercial implications as well as scientific ones. The Southern Ocean is a valuable fisheries resource, many of the species caught feed on krill. Thousands of tourists are also attracted to Antarctica to enjoy the spectacular wildlife, most of which feed on krill.

There has been previous speculation that krill stocks might have decreased, based on smaller more localized surveys over shorter time periods. This new finding comes from data from nine countries working in Antarctica who pooled their separate data covering 40 Antarctic summers, in the period between 1926 and 2003. This is the first time such a large-scale view of change across the Southern Ocean has been seen.

Another animal that feeds on the same phytoplankton food as krill, jelly-like colonial animals called salps that drift in the ocean currents have increased in the same time the krill have decreased.

This decline in krill will also make it more difficult for the great baleen whales to return to pre-exploitation levels following their decimation in numbers during the years from approximately 1925-1975.
Krill adaptations Krill fisheries

Phytoplankton: bar = 0.01mm

Reference: A. Atkinson, V. Siegel, E.A. Pakhomov, M.J. Jessopp & V. Loeb (2009). "A re-appraisal of the total biomass and annual production of Antarctic krill" Deep-Sea Research 56: 727-740.

Picture credits, copyright pictures used by permission: Krill filter - Gerd Alberti & Uwe Kils, Creative Commons Share and Share Alike 3.0 Unported license.

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Antarctic Krill, the engine that powers the Antarctic ecosystem

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Krill is a Norwegian word for "whale food", more than anything else, krill are the engine that powers the Antarctic ecosystem. Krill adaptations Krill are a small semi-transparent crustacean like a shrimp, about 6 cm (over 2") in length and a gram in weight when fully grown, they can live for up to 7 years which is quite remarkable considering the wide variety of animals that feed on them in huge quantities.

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Mysticetes take in a mouth full of sea water and huge numbers of planktonic food such as krill or even shoaling fish They then close their mouths and use the tongue to push out all of the water through the baleen filters which keep the small prey inside, these are then swallowed.

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Emperor penguins are one of the "classic" penguin species that people imagine when they hear the name. Along with King Penguins andAdelie penguins, they are representative of the whole group.

Emperor Penguin Basics

Average Weight: 30kg - 66lb

Average Height: 115cm - 3.8ft

Breeding Season: April - December - Emperors breed in the depth of the Antarctic winter. The average temperature is around -20°C (-4°F) falling as low as -50°C (- 58°F) and with winds that gust up to 200km per hour (124mph).

Reproduction: Emperor Penguins breed almost exclusively on sea-ice near to the coast of Antarctica, rarely on land, the breeding colonies can be up to 200 km from the open sea.

Estimated world population: - 595,000, stable.

Feeding & diet: Eat mainly fish in Antarctica, also krill and squid which can be more important in some places.

Conservation status: Near threatened..

Distribution: Circumpolar, breed right up against the continent.Leopard seals and killer whales- main predators of adult birds. Skuas - prey on eggs and chicks.
Emperor penguin adaptations

What are Emperor penguins like?

Emperor penguins have the upright and regal bearing that their name suggests. They take the dinner-jacketed formality of all penguins to its highest level and though they are able to be as awkward, gawky and get as dirty as other penguins, when they shake it all off and stand up to regain their dignity, there are few if any more stately and elegant animals on earth.

Emperor penguins are the largest of penguin species with an average weight of around 30kg (66lb) but can be up to 40kg (88lb) and a height of approx. 1.15m (3.8ft).

They have colourful feathers around their necks and heads, though are not quite as bright as king penguins which are almost as large. There is little or no possibility of confusing the two species however as their distribution around Antarctica is very different. While king penguins are a sub-Antarctic species, being based on islands dotted around the continent, emperor penguins are animals of the deep south. They are never found together.

Emperor penguins have yellow ear patches that are "open" fading into the white of the breast feathers, whereas king penguins have orange ear patches that are "closed" by a band of black feathers. Emperor penguin chicks have distinctive plumage with a large white face patch.

Where do Emperor penguins live?

All but 3 of about 40 known emperor penguin colonies are on winter fast ice that is frozen solid and attached to the land from autumn until it begins to break up in the spring (though some years it doesn't break up at all). They are found all around the coasts of the Antarctic continent. They breed during the depths of the Antarctic winter and in some of the most desolate, coldest, windiest and downright grim places on the planet during the season of 24 hour darkness. Some emperor penguins are the only birds that never set foot on land.

The first breeding colony wasn't discovered until 1902 by Lt. Reginald Skelton on Scott's 1901-04 Discovery Expedition some 130 years after the birds had first been seen on Captain Cook's second voyage. New colonies were still being discovered as late as 2009. Nowadays satellite imagery is used to find breeding emperor penguin colonies in remote regions.

Early in the 20th century, Emperor penguins were thought to be some kind of evolutionary "missing link", something that scientists thought could be proven by observing the growth of the embryo at various stages. On Scott's 1910-1913 Terra Nova expedition a small group of expeditioners set out on a winter sledging journey led by Wilson, the biologist and including the young Apsley Cherry-Garrard, famously this gave rise to the acknowledged greatest of all Antarctic adventure and travel books " The Worst Journey in the World".

Emperor penguin diving adaptations

Emperor penguins feed on fish, krill and squid which they catch on dives that are longer and deeper than any other penguin or bird species. They can dive to a depth of 1,800 feet (550 meters) and hold their breath for up to 22 minutes. This allows them to reach and exploit food resources that other birds can't reach.

The diving adaptations and abilities of emperor penguins have been widely studied, they have been found to have:

1/ an increased ability to store oxygen in the body
2/ the ability to tolerate low levels of oxygen in the body
3/ the ability to tolerate the effects of pressure.

Emperor penguins tolerate low levels of oxygen during dives that would cause a human to pass out and they experience pressures so great that we would get the bends. Neither of these things seem to adversely affect penguins. Their diving physiology is studied at McMurdo Station at a place called penguin ranch 15 miles out in the sea ice where there is only a single hole in the ice, so the penguins must return there to leave the sea.

A penguin's normal resting heart-beat is about 60-70 beats per minute (bpm), this goes up to 180-200 bpm before a dive as they load up with oxygen, then as they hit the water, the rate drops to 100 bpm immediately slowing to only 20 bpm during most of the dive so they use the stored oxygen in blood and muscles to the maximum effect. On returning to the surface again, the heart rate goes back to 200 bpm probably to pay back the "oxygen debt" they have incurred during the dive.

What is unusual about the Emperor Penguins breeding cycle?

Emperor penguins breed almost exclusively on sea ice and so are perhaps the only species of bird that never sets foot on land.

They begin their breeding cycle when other Antarctic penguins have finished theirs, at the end of April to May. Other smaller penguins at this time head north away from the encroaching winter while the Emperors head south into it. They seem to choose very dramatic sites, a large flat area where they can waddle when carrying their egg or chick on their feet surrounded by high ice cliffs or icebergs that help to give a little shelter from the winds.

Eggs are laid in May and June, they are the smallest egg relative to body size of any bird, being around 0.4kg (1.1lb) just under 1.5% of the mass of an adult bird.

At this point, the males take charge of the egg. No nest is built and the egg is incubated on the feet of the parents, a special fold of abdominal skin covers the egg to keep it warm. The mother penguins then set off back to sea and do not return for nearly four months.

The male Emperors with their valuable eggs sit huddled together on the ice throughout the dark weeks and months of the Antarctic night. The average temperature is around -20°C (-4°F) going down to -50°C (- 58°F) and with winds that gust up to 200km per hour (124mph). The males do not eat at all throughout this time, but just sit and wait and protect their egg, (later the chick) until their mate comes back to relieve them.

Very few people have seen an emperor penguin huddle in the winter in a savage place where ice and cold are king and the penguins spend their days in silence. The only events are changing position in the huddle (see below) and the immense spectacle of the ghostly red, violet and green of the southern lights or Aurora Australis playing in the dark skies above their heads.

Brooding young hatchlings

Returning from a fishing dive

Males can be sat incubating and waiting for over 120 days (average 115), during this time they will lose about 40% of their body weight. They use less energy when asleep which they do so as long as possible, it is not unusual for emperor penguins to sleep for 20 or more hours a day under these conditions - even up to 24 hours a day, to conserve their food supplies and increase their and their chick's chances of survival.

They survive by huddling together for warmth, very unusual behaviour for adults of other penguin species which are usually aggressively territorial. They also take it in turns to occupy the coldest most exposed outside positions. Without this huddling behaviour, they would unable to endure the combined conditions of fasting, bitter cold and hurricane force winds and would not be able to live and breed in the way they do. Even though they are close together during these huddles, they have been recently shown to be not quite touching. if they touched and squashed the puffed out feathers down it would reduce the insulating value and make them colder, so they really fine-tune the process.

It's not all altruistic behaviour though, and taking it in turns. The ones that have been on the outside on the windward side wander off to the leeward side when they've had enough so exposing the next "layer" of penguins. The whole huddle can wander over quite an area in this way in very cold and/or windy conditions.

How do the parents ensure that the chick survives when born on the open sea ice?

As the chicks grow older and get larger, they become able to regulate their own temperature in milder conditions, so they don't need the protection of the brood patch. They form creches and will huddle as the parents do if the weather worsens.

Eventually, the female returns across the sea ice. This usually coincides with the hatching of the chick. Sometimes the chick will hatch before the female returns, if this happens, it will be fed with a secretion of protein and fat produced by the male from its oesophagus a sort of penguin "milk".

The pair locate each other by calling repeatedly, eventually recognizing each others voice, and the male passes the chick over (sometimes reluctantly and after much persuasion) onto the feet of the female. A chick left alone on the ice at this time has a survival time of only around two minutes. The males are then able to go off to sea to feed and build up their strength and fitness again. This journey alone can take several days across the ice. Emperor penguins have been known to walk 280km to reach the sea.

At this point, the chick is reared in the conventional penguin manner, with the parents taking it in turns to feed and look after the chick until they are large enough to leave.

When they are older and larger, the chicks huddle together in creches for warmth and protection while both parents are able to go off to collect food at the same time to provide for the ever increasing needs of the growing chick.

Chick survival has a lot to do with how the ice breaks up and so how easy it is for parents to reach the sea. If the parents have to travel long distances, many chicks will die of starvation. If the ice edge remains close, then the parents will be able to provide more food and the chicks stand a better chance of survival.

The colonies begin to disperse as the sea ice begins to break up in December and January, the chicks are then able to fend for themselves leaving the adults to moult their feathers (a time when they need to stay out of the water) and so are not able to feed.

Why do emperor penguins breed in such severe conditions?

Despite the way it seems, this breeding strategy of the emperor penguin does make sense. Emperors are large birds, twice the weight of the next biggest penguin, the king, and so are able to survive the winter fast and the extreme cold temperatures endured at this time
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With this breeding strategy, the penguin chicks become independent during the height of the summer food supply and so are able to survive better.
The chicks are very large too compared to other penguin species, if they were reared in the summer, they would have to be left to fend for themselves at a time of the year when food supply is reducing. As the chicks food requirement is very high, this would cause major problems.

Emperor penguins are able to raise a chick each year by this strategy, though the rigorous conditions of life in the deep south mean that only 19% of chicks will survive their first year. King penguins on the other hand can expect an 80% first year survival rate, though their breeding strategy means that they rear 2 chicks every 3 years and the requirement for open water year-round restricts their range to sub-Antarctic islands.

Emperors are preyed upon by Killer Whales, Leopard Seals, and the Giant Petrel. The most dangerous predator is the Leopard Seal that can eat about 15 penguins a day though they usually only catch the weak or the very sick. Healthy penguins can usually out-swim a Leopard Seal.
Read about emperor penguin adaptations
There were estimated to be around 238,000 breeding pairs of emperor penguins in the world in 2009. Taking into consideration the non-breeder ratio as well this translates into about 595,000 adult birds. Emperor penguins reach breeding age at 4 years and can live to be 20.

Pictures used courtesy of Warner Brothers or NOAA

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Emperor penguins are one of the "classic" penguin species that people imagine when they hear the name. Along with King Penguins andAdelie penguins, they are representative of the whole group. Emperor Penguin Basics Average Weight: 30kg - 66lb Average Height: 115cm - 3.8ft Breeding Season: April - December - Emperors breed in the depth of the Antarctic winter.