Survival of the coldest
Emperor penguins lay just one precious egg a year in temperatures below -40°C, and they must go to astonishing lengths to keep their chick alive
Every year, at the beginning of breeding season in the Antarctic, each emperor penguin must make a difficult decision: who to choose for a mate. Although these remarkable birds, the biggest of all penguins, are faithful to their chosen partners for the whole season, they do change mates from year to year rather than pairing for life. Scientists call this behaviour ‘serial monogamy’.
The reason is simple. Any bird may arrive at the vast breeding colony earlier or later than their ex – and time is of the essence. Penguins can’t afford to wait around for former partners to arrive: they must choose from whichever potential mates are available.
Having spent the summer months out at sea, hunting for food in the incredibly productive seas, by the end of April, three weeks or so after the first emperors begin to arrive at the colony (which will eventually number some 10,000 birds), temperatures have dropped as low as -35°C, which means the sea ice on which they choose to breed is freezing solid. It is time for the next stage in the breeding cycle – courtship and pairing – to begin so that the chicks will have grown sufficiently before the sea ice begins to thaw in the Antarctic summer.
The male makes the first move. He stands stock still and lowers his head to his chest. Then he begins to call, the sound lasting just a few seconds. He repeats it while walking slowly around the colony, until he manages at last to stir the interest of a female. Male and female then stand face to face, and go through a series of co-ordinated movements, as if each is looking at the other in a mirror. When the male lifts his head up, so does the female; when he lowers it, so does she. Each pose is held for a minute or two, before they change position.
This goes on for several hours over a number of days, until the pair are fully bonded. They will be jointly responsible for raising a single, precious chick, a process that will take another six months or more – if the baby doesn’t get stolen by another penguin (see panel, right). For a long time after pairing up they will still engage in these bonding rituals, often uttering loud calls, to reinforce the link between them.
‘One thing that struck me was how often an individual was rejected,’ says camera assistant Stefan Christmann. ‘The initial call and mirroring display would start, but quite often, after 30 seconds or so, one or other bird would simply walk off. The individual I was watching must have endured this rejection at least four times before I finally lost sight of her in the melee of penguins.’
Once courtship was over, it was time to mate. And that is not easy on the ice. ‘It was like watching a surfing lesson,’ Stefan laughs. ‘The male would try to clamber onto her back, like a human being standing on a surfboard for the first time; but then he would lose his balance and fall off.’ Once aboard, there would be a few brief rocking movements and the whole process was over, almost as quickly as it had begun.
Emperor penguins are different from all other penguins – and most birds – in that they do not build a nest. For a start, there are no materials with which to do so; even if there were, an egg exposed to the outside air would freeze within minutes.
Once the egg is laid, both male and female inspect it carefully, duetting together as if to celebrate. Then, in a tricky and potentially fatal manoeuvre, the female passes the precious egg over to the male. The male uses his beak to pull the egg between his feet and into his brood pouch as she backs away. Having successfully transferred the egg, the pair reaffirm their bonds by calling to one another before the female turns around and heads back towards the ocean, some 25km away, for the rest of the winter. The female will have lost about a quarter of her bodyweight producing an egg, and she desperately needs to feed. ‘As she finally walked away,’ observed cameraman Lindsay McCrae, ‘after a few minutes she would turn back and glance back at the male for a brief moment, as if saying farewell.’ The male will now have to take care of the egg for the next two months – without being able to feed.
As well as keeping the egg warm and safe, the males must maintain their own body warmth. The only way to do this is to form a huddle or rough circle, all facing inwards towards the middle. As new birds arrive behind them, they gradually end up towards the centre, as the individuals there move out when they become too warm. The concentration of birds is truly extraordinary: they squeeze in at densities of about ten birds per square yard, leaving little or no room for manoeuvre. This way, instead of losing their body heat to the freezing air, heat stays within the huddle, so they keep warm. Astonishingly, in the very centre of the huddle temperatures can reach more than 30°C. That’s vastly higher than the external air temperature of less than -40°C.
‘Eventually, temperatures will rise beyond what the penguins can bear, and the huddle will break open,’ explains camera assistant Stefan Christmann. ‘It’s a remarkable sight, because all of a sudden there is a lot of movement, the noise picks up, and a giant cloud of steam emerges from amidst the birds, while they start to spread out flapping their wings. You can tell that they are nicely warmed up, feeling all comfy and relaxed.’
Meanwhile the female, having
THE PARENTS INSPECT THEIR EGG, DUETTING TO CELEBRATE
laid her egg and passed it over to the male, urgently needs to get back to the sea. This is a very long walk which she has to undertake when she is at her lightest and weakest. At last, reaching the ocean, she dives into the water. This is a dangerous moment. Two predators dominate these cold oceans: the leopard seal and the orca, or killer whale. But she has some advantages, in terms of speed, and also camouflage: penguins are white beneath for a good reason, as it makes them harder to spot against the light coming through the water from above.
Emperor penguins feed mainly on fish, squid and krill – but she is not just feeding for herself. Having eaten her fill, she then needs to fill her stomach with as much food as possible to bring back for her chick. By the beginning of August, the females begin to return to the colony. As the characteristic contact calls of the returning partners echo over the ice, the male listens out until he hears his mate.
Then he shuffles forth and engages in a repeat of their courtship bonding display. He has been guarding the egg for almost two months, and it is about to hatch. The female has timed her return to perfection.
The chick spends much of its first month on its mother’s feet. Its weight almost doubles every two weeks. It’s not the only hungry member of the family, though: the male has not fed at all for almost four months.
During the next seven weeks, male and female take turns to return to the ocean to catch food for the growing chick. By December, the pack ice breaks up enough for the sea to be very close to the breeding colony. With open water nearby, it’s time for the chicks to leave their parents and become independent.
It is now a time of plenty with food in abundance and for the emperor penguins, another long and arduous breeding season is finally over.
Dynasties begins on Sunday, November 11 on BBC1
Dynasties: The Rise And Fall Of Animal Families by Stephen Moss, published by BBC Books, €31.40. Adapted for these extracts by Christopher Stevens.