Though the smaller penguins do not reach such depths, for their size their diving performance is just as remarkable. Gentoo penguins dive to 150m, and a quarter of their dives exceed 100m — in extreme cases they can dive almost continuously for 15 hours, completing over 450 dives.

Numbers and breeding

The total number of breeding pairs of penguins in the Antarctic region is estimated to be about 20 million. Although this covers a huge geographical area, the penguins are concentrated in coastal regions. Huddled up in the cold of winter, emperor penguins can reach a density of 19 birds per square metre.

The timing of breeding is crucial for penguins. Unlike humans, which can have babies at any time of year, the penguin breeding cycle is finely tuned, so that chicks hatch and are ready to fend for themselves when food is most plentiful.

They are very sensitive to environmental conditions. Breeding success is usually controlled by the abundance and availability of prey. If sea-ice does not break away, or krill numbers are low, then huge breeding failures can occur, and few chicks survive. Older birds are the most successful breeders.

Why don't penguins live in the Arctic?

To penguins, swimming in warm seas is like walking around in winter clothes in the height of summer! The warm waters of the equator are a barrier to penguins. Even the penguins living close to the equator stick to the cooler water coming from the south. If penguins could travel to the Arctic, they would find their niche already taken by another bird - the puffin. Puffins are also black and white birds with colourful beaks. However, puffins need to be able to fly to escape land-based predators.

Most penguins (except the emperor and king) lay more than one egg, usually two. Incubation duties are shared by both parents, working in shifts until the chick hatches, with varying shift lengths from daily changeovers (gentoo) to over a month (emperor).When they are old enough, the chicks gather together in a crèche, watched over by a few adults. This allows both parents to feed at sea, and provides protection from the cold and predators.

Case study

In 1998, on the island of South Georgia, the gentoo colony had a disastrous breeding year with only 1% of chicks surviving to fledge (40–60% survive in normal years). However, the nearby macaroni colony had normal levels of breeding success. Both species feed mainly on krill, but in 1998 krill numbers were low. The macaroni penguins were able to change their diet to smaller crustaceans which were still plentiful. The gentoos’ other preferred food, the ice-fish, is also krill dependent, so the gentoos had little to eat.

Feathers and moulting

A penguin’s feathers keep it waterproof and warm, and must be well oiled (using oil from a special gland at the base of the tail). How do you monitor a penguin colony?

Firstly, by counting the penguins daily over many months, to find out the timing of events such as egg laying and hatching. With thousands of pairs in a colony, this is not an easy task! When adults return from the sea to feed the chick their diet is analysed. Satellite tracking monitors the location of penguins at sea. All this data is tied in with information about the fish, krill and squid in the nearby waters to build up a picture of how penguins "go about their business".

Feathers become worn out and must be replaced every year. During the 3–4 weeks of moulting, penguins come ashore. Because they are no longer waterproof when they lose their feathers and cannot go to sea to feed, penguins fatten up before moulting, gaining an astonishing 50–70% in weight.

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