While penguins are supremely adapted for an aquatic existence, they are forced to find a balance between two worlds: the sea for feeding and the land for moulting and breeding. Penguins’ feathers insulate them in the water – much like a diver’s dry suit, trapping a layer of air next to the skin – and they must be renewed annually to maintain their performance. Penguins must remain on land as they moult (shedding their old feathers and growing new ones), which typically takes two to three weeks each year. And to keep eggs and chicks warm and protected from predators, parents must take turns staying on the nest on land.
Penguins nest in a variety of ways. The little penguin makes a burrow in soil, or nests in natural cavities. Others nest in forest or scrub among tree roots and litter, while open stone nests on bare rocky ground suffice for other species.
The emperor penguin avoids land altogether, breeding on winter sea ice and using its feet instead of a nest to hold the egg.
The fast life
To be a penguin and to be on land – for moulting or nesting – is to be on a diet. All penguins have a remarkable capacity to fast for days or weeks. Emperor penguins hold the record. The males don’t eat from the start of their courtship until the end of incubation: about four months.
Time at sea
How far penguins must travel for food determines how long they spend at sea between visits to the nest. The yellow-eyed and little penguins are inshore foragers, usually staying within 20 kilometres of their colony. Mostly they are at sea for only a day or two. All of New Zealand’s other penguin species are offshore foragers and, especially when the other parent is incubating the egg, can travel tens or hundreds of kilometres to get the fish, krill or squid they need. This can keep them away for two or three weeks. When feeding chicks they cannot range as widely because they need to return frequently to the nest with food.