How Do Emperor Penguins Survive the Cold? Huddles and Feathers

How cold does it get for emperor penguins?

The emperor penguin breeds in the coldest conditions of any bird. It raises its chick through the Antarctic winter, on sea ice attached to the coast. Air temperatures at the colonies can fall below −40 °C (−40 °F), and gusts can exceed 140 km/h (87 mph), creating a severe wind chill.

The sea is a little warmer but still freezing by human standards, at about −1.8 °C (28.8 °F). Water draws heat away from a body far faster than air does, so a penguin must stay warm both on the ice and while diving for food.

Despite this, an emperor keeps its core body temperature at about 38 °C (100 °F). Between roughly −10 and 20 °C (14 and 68 °F) it needs no extra energy to do so. Below that range it starts burning more fuel, by shivering, moving and breaking down fat.

Feathers: a windproof, waterproof coat

Feathers provide about 80–90% of an emperor penguin’s insulation. The stiff outer contour feathers overlap like roof tiles to form a windproof and waterproof shell. Each one has a fluffy afterfeather at its base, and between them sit tiny down feathers called plumules. Together they trap a layer of still air next to the skin.

Penguins have long been described as having the densest feathers of any bird. A more recent study of emperor penguin skins found fewer contour feathers per square centimeter than the old figures suggested, and showed that the downy afterfeathers and plumules play a major role in keeping the bird warm. The overall coat is still remarkably effective.

Muscles in the skin let an emperor raise its feathers on land to trap more air, and flatten them in water to keep the skin dry. Regular preening spreads oil from a gland near the tail, keeping the coat water-repellent. Emperors molt all their feathers once a year, in about a month, and they stay out of the water during the molt because their coat is not fully waterproof.

Fat and a compact body

Under the skin, emperors carry a layer of fat that can be up to about 3 cm (1.2 in) thick before breeding. Fat insulates the body and is the fuel that keeps a male alive while he fasts for up to four months.

Size also helps. A large, rounded body has a small surface area compared with its volume, so it loses heat relatively slowly. That is one reason the two largest penguins, the emperor and the king, live in the coldest regions, while small penguins live in milder seas. The emperor’s bill and flippers are also relatively small for its size, which further reduces heat loss.

Heat exchangers in the flippers, feet and nose

Emperor penguins use a clever plumbing trick called countercurrent heat exchange. In the flippers and legs, arteries carrying warm blood away from the body run right alongside veins carrying cold blood back. Heat passes from the warm blood to the cold blood, so it returns to the body instead of being lost from the feet and flippers.

As a result, the feet stay cool but just above freezing, and the bird can stand on ice without losing much heat. Emperors often rock back on their heels and stiff tail feathers, lifting their toes off the ice to cut contact even more.

The nasal passages work in a similar way. As the penguin breathes out, its warm, moist breath passes over cooled surfaces in the nose, which recover much of the heat and water before the air leaves the body.

Surprisingly, the outer surface of an emperor’s plumage is often colder than the surrounding air. Thermal camera studies found that the feathers radiate heat to the clear polar sky, so the outer coat cools below air temperature. This shows how well the plumage keeps body heat inside.

The huddle: sharing warmth

When winter storms hit, male emperors incubating eggs press together into dense huddles that can hold hundreds or even thousands of birds. They pack in very tightly, up to about ten birds per square meter. Each penguin turns its back to the wind and tucks its head down.

A huddle is constantly moving. Every half minute or so, birds take tiny coordinated steps, and these movements ripple through the group like a wave. Penguins on the exposed windward side gradually shuffle along the edges to the sheltered downwind side, so no bird is stuck on the cold edge for long. Over hours, the whole huddle slowly drifts across the ice with the wind.

Huddling makes a huge difference. Temperatures inside a dense huddle can rise above 20 °C (68 °F), and sometimes much higher, so birds in the middle can actually get too warm and move outward. By saving energy, huddling males lose weight more slowly, which helps them survive until the females return. Huddling is also linked to another unusual trait: unlike most penguins, emperors do not defend a nest territory, so they can stand close together when warmth depends on it.

How chicks and eggs are kept warm

The egg and the young chick never touch the ice. They rest on a parent’s feet, covered by a warm, featherless fold of belly skin called the brood pouch. An egg exposed to the winter air can freeze within a minute or two. This system is explained in detail in how emperor penguins keep their eggs warm.

At about six to seven weeks old, chicks become too big for the pouch. They then gather in crèches, groups of chicks that huddle together while both parents are at sea collecting food.

Penguins vs Arctic animals

Penguins are not the only animals that face extreme cold. In the Arctic, which has no penguins, mammals such as the polar bear rely on thick fur and blubber instead. The emperor penguin, however, is the only bird that raises its young in the open on Antarctic sea ice through the depths of winter. Discover other species of the far south in our guide to Antarctic animals.