LIFE AND SURVIVAL IN THE COLONY.
In the challenging conditions of Antarctica, life in a colony offers many survival advantages for penguins. First, safety in numbers. With multiple eyes and ears alert for danger, the colony is quick to rumble predators such as lurking leopard seals and scavenging giant petrels. By sticking together, individuals are less vulnerable to attack. On land, Adélie penguins will join ranks to chase away predators; when fishing, they enter the water in groups, swimming close to one another, and all return to the safety of land – or ice floe – at roughly the same time.
For emperor penguins, colonies also provide protection from the elements. When freezing Antarctic winds whip across the ice, the birds form a tight huddle, called the turtle formation, in which each individual leans into its neighbour for warmth and shelter. Vulnerable juveniles remain at the centre. The others move in a continuous slow-motion rotation, those on the windward side shuffling around the edge of the group to the leeward side where the wind is less fierce. By cooperating as a group in this way, every individual increases their chance of survival.
Penguin colonies aren’t hierarchical – there are no alpha individuals in charge. During the breeding season, however, males and females must pair up.
Getting the message across
To find a mate, a male emperor will wander around the colony, stopping at regular intervals to utter his ‘ecstatic’ courtship call: he’ll let his head fall to his chest, inhale, point his bill to the sky and call for one or two seconds, then continue walking. Once a female shows interest, the two peel off from the crowd and perform a choreographed face-to-face ritual in which they mirror each other’s movements for several minutes until the bond is forged.
They then waddle around the colony together. In a crowded, noisy colony, established penguin partners can recognise each other by their unique calls. In emperor penguins, vocalising is particularly important, as pairs don’t build a nest so have no fixed location at which to meet.
This species has evolved the widest variation in calls of any penguin, with a unique ability to use two frequency bands at the same time. This not only allows adults to locate a partner by their distinctive individual voice, wherever they happen to be, but also helps parents to locate their offspring – and vice versa.
Adélie penguins use a range of calls and moves in their courtship, too, and will also deploy props to help strengthen their pair bonds. This species makes a nest of pebbles, which a pair gathers laboriously at the start of the breeding season. When a male is about to head out fishing, he’ll often bring back a few more pebbles to offer the sitting female. This proves to her that he’s a reliable and hard-working partner – one worth sticking with.
Watch your back!
Of course, the flipside of cooperation in a colony is competition.
Resources are often in short supply and each breeding pair will do all it can to increase its own chances of success. To this end, Adélie penguins may steal pebbles from their neighbours’ nests to fortify their own, thus saving the energy they’d otherwise expend on long pebble-collecting expeditions. When pebble thieves are caught in the act, they get a hard time from birds on all the neighbouring nests. Nests nearer the edge of a colony – where thieves are more likely to get away with their crime – are thus the ones most vulnerable to attack. And those left with fewer stones are less likely to experience breeding success.
Emperor penguins sometimes take theft to another level. Females that have failed to breed or have lost their own chick may attempt to steal another pair’s chick. If a chick becomes separated from its real parents, it may even find itself pursued by a gaggle of such females attempting to ‘adopt’ it as their own.
This bizarre kidnapping behaviour is thought to arise from this species’ unusually high levels of the ‘parenting’ hormone prolactin, which is what drives females to return to their chick after a long period at sea. For a kidnapped chick, things seldom end well: the adoptive parent soon loses interest, and, separated from its own parents, the youngster is left to starve. Thankfully, emperor penguins are very protective parents and a pair will defend their chick vigorously against any would-be kidnappers
