Emperors on ice
Many birds migrate to escape the rigours of winter. Not so emperor penguins. Each autumn they march towards breeding sites on the edge of Antarctica, where they will raise their young in the freezing darkness of the harshest winters on earth.
There’s something very special about emperor penguins. They live, and raise new life, in one of the harshest environments imaginable. Their story is one of nature’s triumphs, of creative solutions at the very edge of what is possible.
No other warm-blooded animal endures such cold as the emperor. In autumn, when the emperors march towards the Antarctic continent to begin their long breeding cycle, all other life shuts down, or swims away, or flies north, or heads into the warmer sea. Weddell seals stay for the winter too, but spend most of it underwater, breathing through cracks and holes in the sea ice which they keep open with their teeth. Only emperors meet the winter head on.
Emperor penguins not only manage to live where no other animal even tries, but do so in remarkable style. The largest of all penguins, and certainly one of the most handsome, they go about their lives with such a calm dignity that it’s hard not to like them. And impossible not to fall in love with their chicks.
Emperors may be easy to like, but they aren’t quite so easy to find, let alone study. There’s something like half a million of them spread around Antarctica: 200,000 breeding pairs plus an unknown number of non-breeders. They mostly breed in inaccessible places, and in the darkness of winter, so their colonies haven’t been easy to locate. To date, some 40 colonies have been discovered around the Antarctic coastline, and new ones are still being found. Three new colonies were discovered in the Weddell Sea in 1986, one with 11,700 chicks, and there are almost certainly colonies still awaiting discovery along the poorly-explored Marie Byrd coastline.
Although emperor penguins have been known to science since 1840, the first colony wasn’t discovered until 1902, when members of Scott’s first Antarctic expedition found the birds at Cape Crozier. This small colony, the world’s southernmost, lies on the eastern tip of Ross Island in the Ross Sea, directly south of New Zealand. Scott Base, New Zealand’s main presence in Antarctica, lies 85 kilometres away.
Before 1991, no-one had ever seen the colony in winter, apart from members of Scott’s second Antarctic expedition who, in 1911, almost lost their lives on what would later be described as “the worst journey in the world.” Robert Swann’s “Footsteps of Scott” expedition visited Crozier in the winter of 1985, but was unable to find the colony in the darkness, the wind, and the bitter cold.
The Worst Journey in the World is one of the all-time classic tales of exploration and survival (see box), and the emperor penguins are a survival story on their own. Why not combine the two in a major documentary? thought Television New Zealand’s Natural History Unit. So they did. From January to December 1991, one of their film crews made 13 visits to Cape Crozier. filming the emperors’ arrival, breeding, and return to the sea.
Over the previous summer, teams from Scott Base had installed two solid little huts on the slopes of Cape Crozier, overlooking the colony. They also surveyed and flagged the entire 85 km route from Scott Base to the huts, placing fuel dumps at marked depots along the route. On each week-long trip, Max Quinn (film director and camera) and Don Anderson (sound) were accompanied by a support team from Scott Base.
I joined them in September. Max and Don already had some great film “in the can,” including behaviour never filmed before. Guided both by the flagged route and satellite navigation, we made the trip in seven hours, travelling in the heated comfort of Hagglunds oversnow vehicles. We planned to spend three full days at the colony, but in Antarctica nothing is ever certain until it happens. On previous trips, the film crew had spent nearly all their time cooped up in the huts, waiting out blizzard after blizzard. In Antarctica you get good at waiting . . .
Our first day, An hour after leaving the huts we are down among the emperors. I check the small thermometer hanging from my jacket: minus 30°C, but the air completely still, the sky cloudless. A perfect spring day. Seven to eight hundred emperor penguins stand spread out on the sea ice between the low canyon walls of the Ross Ice Shelf.
Penguin colonies are usually noisy, messy, seemingly chaotic places, but emperor penguin colonies—like the birds themselves—are very different. For the most part, the adults stand still, regal and silent, or shuffle slowly. Most are harbouring chicks under their belly feathers. These are the mothers; the fathers are out at sea, recovering from their recently-completed marathon fast. For three-and-a-half to four months, the males have courted, mated, and then incubated a single egg right through to hatching, eating nothing except the occasional mouthful of snow for its moisture.
The chicks, just a few weeks old, are endearing balls of fluff which are fast outgrowing the space between their parent’s belly feathers and feet. They will stay in this downy hideaway until they are about six weeks old, each day wriggling an ever-larger body into a space that has definitely grown smaller overnight.
Filling the crisp air are the sweet chirrupings of chicks who have just found enough room in their big stomachs for another meal. Stretching as tall as a two- to four-week-old chick can stretch, craning up towards the source of all seafood takeaway meals, and waving its head from side to side, each chick begs mother yet again: “Food please, food please, food please . . .” Food and warmth—the needs of a young emperor penguin are pretty simple, really.
It is now some weeks since the mothers’ last meal out at sea, and each is living off her fat reserves, somehow managing to not digest the food in her stomach—that is all needed by the chick. Finally, after endless pleadings from junior, mother regurgitates another meal of fish, squid and krill into the waiting throat. Full again, the chick settles back contentedly to digest the latest offering. Sometime later, still on mother’s feet, it is taken for a walk around the colony, stopping now and then to pass the time of day with other chicks—the mothers standing face to face high above the young ones.
The Cape Crozier area is notorious for its bad weather; “a breeding place of wind and drift and darkness” was how one of Scott’s men put it. But Antarctic weather is often much better than people imagine. When it’s bad, it’s a frozen hell of wind and snow and cold; grim and merciless. But there are also many, many days when the wind hardly stirs and the sun shines dazzlingly through the cleanest skies on this planet. On days like that it is a magical, entrancing place.
Especially Cape Crozier. From the gently sloping shoreline where 180,000 Adelie penguin families raise a new generation each summer, the rocky slopes and snowfields rise grandly towards the summit of Mount Terror, an extinct volcano. Apart from summer visitors—Adelie penguins and skuasnothing but the occasional sliver of life can exist on these slopes: a few inconspicuous algae, the odd moss, some wrinkled lichens.
To the north of Cape Crozier lies the Ross Sea. In summer, it is the world’s southernmost open sea, but in September it lies frozen for 1500-2000 kilometres to the north. Antarctica’s encircling fringe of sea ice reaches its maximum in September or October, doubling the size of the continent.
But even in the coldest winter, Antarctica is never completely surrounded by solid ice. Wind, current, and local geography (coastlines and sea floor) combine to continually move the ice, to make cracks, leads, and ice-free areas, allowing emperor penguins to feed year-round near the coastline. Large areas of open water, or of markedly reduced ice cover, are called polynyas. These are normally stable features, occurring in the same place year after year. The largest of three polynyas in the southwestern Ross Sea lies northeast of Cape Crozier.
Sometimes emperors have to travel very long distances—up to 200 kilometres or even more—to find open water, but it’s usually out there, somewhere. It doesn’t need to be large. A crack or hole just big enough to let an emperor through is all they need. But if they can’t find it, they are in big trouble. One year, the sea froze solid for over 500 kilometres in every direction around an emperor penguin colony at Pointe Geologie, in another part of Antarctica. That was too far for the parents to shuttle back and forth to feed their chicks, 90 per cent of whom died.
When I visited Cape Crozier, the emperors were having it easy. There was open water just seaward of the ice front, a couple of kilometres from the colony. The comparatively warm seawater (minus 1.85°C) was “smoking” in the cold air, forming a low fog over the open water.
Cape Crozier juts out towards the edge of the massive Ross Ice Shelf (“The Barrier”)—a huge floating glacier twice the area of New Zealand, and the largest ice shelf on earth. At the ice front, underwater melting has thinned the sheet from perhaps a kilometre thick where it leaves the continent to about 100 metres. Spreading over the sea at up to three metres per day, part of this moving ice sheet finally meets the immovable Ross Island.
As it approaches the coastline near Cape Crozier it buckles into pressure rollers, like frozen ocean swells, up to 15 metres high. Along the coastline, the ice shelf grinds itself into a chaos of freeform ice sculptures which are difficult and dangerous to move through. Near the Cape, the surface of the ice shelf is pitted and patterned by a combination of wind, summer melt and windblown dust. The result looks more like the surface of the moon than anything earthly.
Finally, the ice shelf reaches the ice front, an 800-kilometre line along which it breaks up into icebergs-150 cubic kilometres-worth every year, on average. In 1987, a giant iceberg 154 kilometres long and 35 kilometres wide broke away from the Ross Ice Shelf. Significantly changing the coastline in one massive break, this iceberg contained enough frozen water to fill Lake Taupo 40 times.
Near Cape Crozier, the ice shelf develops several major cracks. In autumn, the sea freezes inside these long cracks, forming low-walled canyons that afford good shelter and secure ice for the emperor penguin colony. Always a small colony, its numbers have fluctuated wildly over the years, from a high of around 1500 pairs in 1961-62 to a low of 46 pairs in 1976. The colony’s size and breeding success depends to a large extent on the amount of shelter and stability afforded by the ice front. In 1902 and 1903, and again in 1911, there were no deep sheltering bays or welcoming canyons in the ice shelf. The very small colony then was sheltered from southerly winds by the high ice cliffs, but exposed to the north. If the sea ice had broken out early, the eggs or chicks would have drifted away into oblivion.
Halfway through our second day with the penguins, I gain an insight into an emperor’s life during winter, though without the darkness and extremes of temperature. With little warning, icy fingers of wind reach over the ice shelf and down into the canyon. The canyon floor, hard sea ice, becomes a wide river of moving ground fog as the wind lifts the dry snow into the air. The blowing snow wafts like silky scarves around the penguins. Stronger gusts envelop the birds completely.
As the wind sharpens, there is little obvious reaction from the adult emperors, other than turning their backs to this frequent, though hardly welcome, companion. Emperor penguins rarely do anything in a hurry, and even an impending blizzard brings no hastiness. Shuffling along so as not to lose their precious baggage, most of the mothers coalesce into a loose huddle within minutes. The nonbreeders that normally hang around the edges of the colony react more definitely, forming a small tight huddle, separate from the main group. Huddling is the emperor’s instinctive, unique, and highly successful defence against the harshest climate on earth.
When the wind hits, the chicks suddenly lose all interest in the outside world, turning around on their mother’s feet and burying their heads as far back into the warmth as they can. The trouble is that chicks more than a week or two old simply don’t fit under their mother’s belly feathers any more. The result is a collection of downy backsides protruding out from their parents’ “pouches.” A covering of windblown snow just adds to the comical effect. Later, as the wind drops, the little faces reappear, the huddles dissolve, and the colony spreads out again.
Only two penguin species—emperors and Adelies—breed in large numbers in the Ross Sea. Each species has its own solutions to the problems of breeding so far south.
Being much smaller than emperors, Adelie penguins (average weight 5 kilograms, compared to 30 kilograms for emperors) are able to squeeze their entire breeding cycle into the short summer, though only just. Penguins in warmer climes—and birds in general—look after their young until they are about adult size. In Antarctica (apart from on the warmer Antarctic Peninsula) there simply isn’t time for that, and both Adelies and emperors fledge their young at well under adult weight. The juveniles then complete their growth independently in the pack ice, at a time when food is still plentiful and easily found. Emperors fledge the smallest young—relatively—of any penguin, letting them loose into the big wide world at only 50-60 per cent of their adult weight.
One major difference between the two life cycles is a function of the size difference between the birds. The large emperors are capable of living in much colder conditions than Adelies are (big bodies lose relatively less heat), but are unable to compress their breeding season into one summer. Chicks simply cannot grow that fast. In order to release their chicks when food is most plentiful, the earlier events of mating and egg laying have to be set well back in the year. Incubating the egg through the bitterly cold winter may sound crazy, but is the only solution for a large bird living all year round near the Antarctic coastline.
King penguins, close relatives of emperors, have some of the same problems, but solve them quite differently. At an average weight of 15 kilograms (making them the second largest penguin) they are also too big to fit their breeding cycle into a single summer. But the kings breed in warmer latitudes, and this allows a different approach. Kings rear their chicks over the longer spring and summer (like “normal” birds), feed them just enough over the comparatively short and mild winter to see them through, and then release them after a final fattening up in spring.
By late february, the sun is circling low around the sky, and starts dipping below the horizon at midnight. Antarctica’s brief summer is over, and the days start to bite. The sun gives less and less heat until, in late April, it skims the horizon for the last time. The emperors won’t see it again until late August.
Apart from a few projects that run year round, most Antarctic science is a frenetic burst of activity during spring and summer, reflecting Antarctica’s own blossoming then. This is also the easiest time to move scientists to and from Antarctica, and get them out into the field. Nearly all studies at Cape Crozier have been during this time, and from these we know that much of the breeding cycle runs up to a month later than at northern colonies. But no-one had ever seen the emperors arrive at Cape Crozier, so the film crew weren’t sure when this would happen.
Their first filming trip to Cape Crozier was in the last days of March. By this time most of Antarctica’s emperors have already gathered at their northern colonies. But there were none at Crozier, just some late-developing Ad4lie chicks that had probably left their run too late. The predatory skuas would mop them up and then fly north. Antarctica in late summer is a huge ship of ice being deserted by its summer crew. Its skeleton winter crew is small, widely scattered, and very hardy.
On April 15, there were only 50 emperors at Cape Crozier, but from then on they arrived in a steady arrived in a steady stream, averaging 50 birds daily until, by early May, over 1000 birds huddled together in the minus 4045°C cold. They marched towards the colony in single file, at slightly slower than human walking speed,or tobogganed on their bellies, a little faster than our walk. They had come from far out in the rapidly freezing pack ice, guided homewards by navigation systems we still don’t understand.
Out in the pack ice, as in the open sea, there are few obvious clues to navigate by, other than the sun wheeling around the sky. For a bird standing a metre high the horizon is only two nautical miles away. Even what looks real often vanishes when approached. Mirages hover over the flat horizon, creating coastlines and mountain ranges where none exist. Spirit kingdoms in the air.
However they manage it, the emperors arrive back at the right time in the right place (often the colony they were born in) to seek a mate. The majority of birds form new alliances each year, going through a four- to six-week courtship phase at the beginning of the breeding cycle to “cement” the relationship.
Courtship is a stately blend of body movements and song. Emperors have a trumpet-like call, which they use as for vocal identification. Emperors are the only penguins which do not defend territories—winter cold demands they huddle together, not stay apart—so noise is not used to assert territorial claims. However, in larger colonies partners need to find each other among tens of thousands of other birds, all of which are continually moving around and calling to each other. Having only their songs to guide them in the darkness, it is not surprising that the calls contain individual nuances which act as “signature tunes”. There are also distinct differences between the calls of males and females.
Emperor penguins are the only birds in the world that may spend their entire life without touching land. All but two of the 40 or so known colonies are on fast sea ice—ice anchored to sheltering coastline or grounded icebergs. The two exceptions are on flat, hard-packed snow over rock. Emperors need open, flat space for huddling, and they need to huddle to make it through winter.
The emperor breeding cycle is closely tied to the sea ice cycle, the colonies assembling as soon as the newly formed autumn ice is thick enough to support their weight. Like many aspects of the emperor’s life, the choice of breeding site is a compromise, in this case between sea ice stability and proximity of food. Being near open sea, and hence food, is of no use if the sea ice breaks up under the colony and drifts away. Likewise, sheltered places with stable sea ice are of no use if too far from food.
After mating, the colony falls silent until the eggs are laid in June. Duets are then performed by each pair to strengthen their bonds, and remind them once again of “our song”—a song they must remember for nine weeks while the male incubates the egg alone. Soon after laying, the male takes the egg, rolling it up on to his feet with his long curved bill. Protected by a large flap of feathered belly skin and warmed against a patch of bare abdominal skin, the egg will be kept at temperatures higher than 30°C, even when the winter air just a few centimetres away drops as low as minus 50.
As long as the egg stays in the father’s brood pouch it is safe. But those feet are not designed solely for egg holding, and are smaller than ideal. Larger feet might hold the egg more securely, but would lose more heat, too. Compromise again. So the father shuffles, not walks, slowly and awkwardly.
The 400- to 450-gram emperor egg is the smallest laid by any bird, relative to body size. It weighs a mere 1.5 per cent of the mother’s body weight, compared to as much as 25 per cent for a similar sized egg from the little spotted kiwi—which comes close to having the largest egg, proportionally, of all birds. After egg transfer and final duets, it is time for the female to head for the sea, often many days, possibly even weeks, away. She has lost 20 per cent of her body weight, and needs to fatten up again before the egg hatches.
Egg-laying is more or less synchronised, so the females are able to leave in groups, heading off in single file over the sea ice. The same instinct that leads to huddling keeps them together in long lines threading out over the ice.
With their mates gone, the males settle down to perhaps the most astonishing breeding vigil in the world: two months of incubation while the Antarctic winter rages around them. Their survival is due to a combination of many remarkable adaptations. They are large and rounded—factors which reduce heat loss. Their waterproof feathers overlap like tiles on a roof and are strong enough to withstand the worst blizzards. Though only a centimetre thick, they provide 85 per cent of the emperor’s insulation. The layer of fat under the skin provides the other 15 per cent, and doubles as a food reserve. Their extremities—feet, flippers, head and bill—are all small, relative to body size; another heat-saving adaptation. In feet and flippers, warm arteries run alongside the cold veins, precooling the blood on its way to the extremities and warming it on its return. Similar heat exchangers are found in the sinuses, where the air breathed out warms the air breathed in, allowing the recovery of an amazing 80 per cent of heat that would otherwise be lost with every breath.
But the strangest adaptation of all is huddling. On windless days, the males stand apart, but as soon as the wind increases, the birds pack tightly together: ten big birds per square metre in an interlocking formation described mathematically as “hexagonal close packing.” Penguins within the huddle reduce their exposed body surface by up to five-sixths, cutting heat loss by as much as 50 per cent and allowing the fat reserves to last much longer.
Huddles are remarkable acts of cooperation and nonaggression on a level rarely met in either animal or human societies. Individuals take their turn acting as windbreaks on the coldest, windward side, before shuffling around the huddle to the sheltered side. Here they are slowly absorbed into the warm middle as more and more birds pack around them, until eventually they find themselves back on the cold side again. The continual stream of birds moving from windward to leeward shifts the whole huddle slowly downwind, as much as a hundred metres per day of blizzard. At large colonies, each sleepy huddle contains up to 6000 birds, but at Crozier the 400 or so breeding birds all huddle in one group, while juveniles and nonbreeding adults gather in smaller groups.
During the male’s fast, every squid and fish caught the previous summer becomes vitally important, possibly the difference between breeding success and failure. Weighing anywhere between 30 and 45 kilograms at the start of the breeding season, males have lost up to 45 per cent of their weight by the time their mates return in spring. If their body weight drops to about 22 kilograms they have no choice but to leave the egg (or chick) to its fate and head for the sea.
When examined closely, all aspects of the emperor’s extreme life do, perhaps surprisingly, make sense. The choice of colony site is a compromise between sea ice stability and food availability. The long travelling times between colony and food leave no option but long, solitary vigils for each partner. And the male is the logical choice for the long winter watch, both by virtue of his greater fat reserves and by the fact that he has not burnt up energy producing the egg.
Being the southernmost emperor colony, the Cape Crozier birds endure the longest, darkest, and probably coldest winter of any of the colonies. For four months the sun stays firmly below the horizon. The only light comes from stars, moon, dancing curtains of aurora and a faint glow on the northern horizon each midday. During August, the midday twilight gradually grows longer and brighter until, on August 19, the sun makes a much-awaited reappearance. Squashed flat by the laws of atmospheric physics, the orange disc briefly brushes the frozen horizon. Each following day its low, flat path sweeps higher and wider across the sky until, by late October, it will no longer set, but freewheel for four months around the bright summer sky.
The Cape Crozier eggs hatch in late August or early September, up to a month later than in northern colonies. For the first few days, the males feed their silver-grey bundles with a milky secretion from the crop. The females normally arrive about now, sleek and fat, ready to take over from their starving partners and feed their young for the next three to five weeks of their lives.
The reunion between partners is not without some awkwardness. Seemingly dazed by the rigours of his vigil, the father is less than enthusiastic about handing over the chick. HIS chick. The bond between father and offspring is so strong that only after repeated advances from the mother will he yield the youngster. Even then he won’t leave for another day or two. But finally he wanders off, thin and scruffy, to look for the sea, possibly still several days away.
Mother feeds the chick until father’s return. From then on, the pair run a shuttle service, delivering meals at intervals determined by the distance to open water.
Mortality is high, even in “normal” years. During winter’s darkness, some eggs are broken or lost during transfer. Eggs and chicks are blown away in storms or abandoned by parents. In 1903, Edward Wilson found that blizzards during September and October had killed 100 of the 130 chicks at Cape Crozier. Storms may do more than just buffet the birds. On occasions, they may break out the sea ice from under the colony. One spring, scientists visiting Crozier found no chicks at all, just adults huddled together. An earlier storm had presumably broken out the ice—and with it all the eggs. Some chicks simply starve, the parents unable to keep up with the constant demand for food—especially if the sea ice remains frozen for long distances.
But perhaps the saddest way for chicks to die is by being “chick-napped.” Emperors have amazingly strong incubation instincts, necessary for their demanding breeding regime, but leading to strange consequences. During winter, while most males are incubating healthy, fertile eggs, a small number may be sitting on abandoned frozen eggs (which then thaw, go rotten, and burst) or even lumps of ice or rock about the right size. Less harmless, however, is the chicknapping that starts once the chicks are born.
The winter fast is hard on fathers, and some just don’t make it through to summer. This leaves fewer males than females, so next season, some females will not find mates. These “spare” females, plus any parents who have lost their own offspring, wander around the colony looking for young chicks to steal from their parents. Desperate for young of their own, they pounce on any chick leaving its parent for even a few seconds. These would-be foster parents often roam in groups—unruly street gangs ready for action, and violence if necessary. Some will even body-charge unsuspecting parents, knocking them off their chicks.
When several mavericks pounce on a chick, a scrum develops, even more dangerous than its rugby counterpart. Many chicks are injured, and some are killed in these mauls as up to a dozen adults try to push the chick under their belly feathers with their pointed bills. Once a chick is tucked under an adult (any adult) the scrum immediately breaks up—until the next skirmish.
A lucky chick eventually ends up back under its own parent’s belly feathers, shaken perhaps, but otherwise none the worse for wear. Being permanently chicknapped by a maverick, though, is the kiss of death. Without a mate to share brooding and feeding duties, the maverick must eventually leave for the sea, abandoning the chick to its inevitable death. I watched dozens of chicknapping attempts at Crozier, one of them resulting in much blood on both chick and a dozen would-be foster parents.
As Antarctica warms, the sea ice starts breaking up, making for shorter walks between colony and open sea. And as the light increases, the pulse of life quickens under the sea. Masses of tiny drifting plants (diatoms and other phytoplankton) multiply rapidly, feeding exploding populations of small grazing animals (zooplankton) which in turn feed the larger life forms that come to feast on the plenty.
When the rapidly growing chicks are five to eight weeks old, they leave their parents and gather in crèches. With both parents now free to go fishing, and open water now normally closer at hand, the chicks receive more frequent meals. If the sea ice doesn’t break up close to the colony, the travel time for each parent will still be long, and the chicks may get as few as a dozen feeding bouts in total—though each could be up to 30 per cent of its own weight.
By December, the Crozier chicks weigh around 10 kilograms and begin moulting into their juvenile plumage, a dull version of the adult plumage. As their parents wander off for the last time, the chicks are left to make their own way in the world. At some colonies this means a long walk over sea ice to reach open water, but at Crozier the sea ice usually breaks up under them about the time they were thinking of leaving anyway. So the Crozier youngsters swim away, or drift off on ice floes, looking far too young to be on their own. Large patches of down still cling to their waterproof feathers, and they weigh little more than half their adult weight.
Emperor young normally become independent at about five months but, remarkably, these Crozier juveniles are only four months old. Earlier parts of the breeding season were up to one month later than in northern colonies, but the juveniles still fledge and leave in December, as they do in other colonies. Maybe the open sea near Cape Crozier for much of the season enables bigger and more frequent meals than at other colonies, allowing the chicks to grow that much faster.
At sea there is much to be learnt. Instinct and rapidly accumulating experience will transform madly flapping juveniles into superb divers, capable of staying under for up to 20 minutes and diving to over 450 metres—far deeper than any other bird.
The first year will be tough, and many, possibly three-quarters, will not survive. Those that do will be back to breed in 4-6 years, but will visit the colony before then. Of those reaching maturity, most will live for 20-30 years; some will reach 50.
Fifty years of the cruelest winters on earth. Of fasts and forced marches. Of fending away mavericks and guarding precious life. These emperors are truly worthy of the name.