How do penguins stay warm?

A bird that lives in the sea

Penguins are birds, but they cannot fly. They swim instead, using their wings as flippers. A little penguin spends about 80 per cent of its life in the ocean. It comes ashore only to look after its burrow, raise chicks and moult, which means to replace its old feathers.

That makes staying warm a big job. A penguin's body is warm, but the sea around it is much cooler. Water pulls heat out of a body much faster than air does. You may have felt this in a swimming pool. The water can feel chilly on a day when the air feels warm. Near Antarctica, the Southern Ocean can be as cold as minus 1.9 degrees Celsius.

Penguins have more than one trick. A waterproof coat of feathers holds in a layer of air. A layer of fat sits under the skin. Special blood vessels stop heat from leaking out through the flippers and feet. Some penguins also huddle together. Let's look at each trick, starting with the penguin that lives in Australia.

The little penguin is the smallest penguin in the world. It weighs about 1 kilogram, the same as a bag of sugar. It stands roughly 30 to 40 centimetres tall. It is also the only penguin with blue and white feathers instead of black and white. Little penguins live along the southern coast of Australia. Phillip Island (Millowl) in Victoria has the biggest colony in the world, with about 40,000 penguins on the Summerland Peninsula.

A coat that traps air

A penguin's feathers are not like a parrot's or an eagle's. They are short and stiff, and they lie flat and overlap, a bit like tiles on a roof. Close to the skin there is a layer of soft, fluffy down. The down holds air between its tiny fibres, a bit like the stuffing in a doona or a sleeping bag.

Why does trapped air help? Air does not pass heat along well, so a thick layer of still air works like a blanket. It keeps the penguin's body heat in and the cold out. When a penguin rests on the sea, the trapped air helps it to float, too.

The coat must be waterproof as well. Near the base of its tail, a penguin has a gland that makes oil. The penguin picks up the oil with its beak and spreads it through its feathers. This is called preening. The oil helps the feathers keep water out, so the air layer stays dry.

Feathers wear out, so each year a little penguin has a moult and grows a whole new coat. At Phillip Island this happens between February and April. First the penguin eats lots of fish and puts on weight, sometimes almost doubling it. Then it stays on land for about 17 days. It cannot swim or hunt while it moults, because its coat is not fully waterproof until the new feathers are in.

Fat and clever blood vessels

Under a penguin's skin there is a thick layer of fat. This is sometimes called blubber. It works a bit like the insulation inside the walls of a house. An emperor penguin, the biggest penguin of all, has a fat layer about 2 centimetres thick. It is thickest in summer, before the winter begins.

Flippers and feet are a problem, because they are thin and lose heat quickly. Penguins have a clever fix. In a flipper, the vessels carrying warm blood out run right beside the vessels bringing cooler blood back. The warm blood hands some of its heat to the cooler blood as they pass. That means the heat goes back into the body, not out into the sea. The feet work in a similar way.

Scientists have studied this in little penguins. They found that each flipper has three blood vessels carrying blood out. They run side by side, and each one has at least two returning vessels beside it. The flipper stays cooler than the rest of the penguin, so it loses less heat to the water.

Huddling through an Antarctic winter

The emperor penguin lives on the sea ice around Antarctica. In winter, the female lays one egg and heads to the sea to feed. The male keeps the egg warm on top of his feet, under a flap of skin called a brood pouch. He stands on the ice in temperatures below minus 40 degrees Celsius. The wind can blow at up to 200 kilometres an hour, and it can be dark for up to 20 hours a day. He may go without food for up to 115 days.

To cope, the males stand in tight groups. This is called a huddle. In a storm, the middle of a huddle can climb above 20 degrees Celsius. That is as warm as a mild spring day, even when the air outside is far below zero.

But who stands on the cold outside? The huddle has to keep reorganising, so that every penguin gets a chance to be inside. A team of scientists, including one from the Australian Antarctic Division, filmed a huddle with time-lapse cameras. They found that the penguins pack in tightly, with about 21 in each square metre. A square metre is about the size of a big bath towel. Every 30 to 60 seconds, the penguins all take small steps of 5 to 10 centimetres, a bit like a Mexican wave. Bit by bit, these small steps reorganise the huddle, so each penguin gets a chance to spend time inside, where it is warmer.

Little penguins: burrows, dusk and hot days

Little penguins do not have to face an Antarctic winter. They spend most of their time at sea, fishing. When they are on land, they stay in burrows during the day. A burrow is a hole in the ground that they dig and line with plants. It gives shelter from hunting birds and from extreme heat. Late in the day, the penguins that have been fishing gather in the water near the shore. They wait until dusk, then waddle up the beach together. Waiting for the dark helps them to avoid birds such as gulls and sea eagles. This is the famous Penguin Parade at Phillip Island.

In a Victorian summer, the problem can be too much heat. A coat that keeps cold out also keeps warmth in. The riskiest time is the moult, from February to April. The penguin is heavy, it is growing a new coat, and it spends about 17 days in its burrow. Dr Peter Dann led penguin research at Phillip Island Nature Parks for about 40 years. He has said that a burrow that reaches 35 degrees Celsius or more can be dangerous. So researchers from the Nature Parks and La Trobe University put 150 small temperature recorders across the Summerland Peninsula. These help them find the coolest places for new burrows. They also installed artificial burrows with different insulation and air flow, to test which ones stay coolest.

People can harm a penguin's coat too. Even a little oil from a ship's fuel can make a gap in the feathers. Water gets in through the gap, like a hole in a wetsuit. Then the penguin loses its warmth. Phillip Island Nature Parks lists oil spills as one of the dangers for little penguins. When oiled penguins are rescued, helpers wash them until their feathers lie flat and waterproof again.

📚 Words to know

Insulation

A layer, such as trapped air or fat, that slows down heat escaping from a body.

Preening

When a bird cleans and arranges its feathers with its beak, spreading oil from a gland near its tail.

Blubber

A thick layer of fat under the skin of a sea animal, which helps to keep body heat in.

Huddle

A tight group of animals standing close together to share their warmth.

Moult

When a bird loses its old feathers and grows a new set.

🧪 Try this: build a blubber glove

1. You will need three zip-lock bags (two that fit inside each other, and one plain one), a tub of solid vegetable shortening or Copha, a big bowl, ice cubes, tap water, a thermometer and a timer. Ask a grown-up to help.
2. Make the blubber glove. Spoon about a cup of shortening into one zip-lock bag. Push the second bag inside it and squash it down, so the shortening spreads out evenly between the two bags. Put your hand into the inner bag. The shortening around your hand is the penguin's fat layer.
3. Fill the bowl with cold tap water. Add a few ice cubes at a time, and ask your grown-up to check with the thermometer until the water is about 10 degrees Celsius. Never use water colder than 10 degrees Celsius. If it is colder, add some warm tap water. Put your other hand into the plain bag.
4. Now lower both hands into the cold water at the same time, and start the timer. Keep the tops of the bags above the water, so no water gets in. Which hand feels cold first? Take each hand out straight away when it starts to feel uncomfortable, and never keep a hand in for more than about a minute. Write down how long each hand lasted.
5. Challenge: test a waterproof coat. Cut two squares of kitchen paper towel. Rub a tiny smear of cooking oil on one square. Add a few drops of water to each square with a spoon. What happens to the drops on the oily square? A penguin's oil helps its feathers keep water out in a similar way.