Every penguin starts as an egg on land and grows into an ocean hunter that returns to shore only to breed and to replace its feathers. The life cycle is a loop between colony and sea, with parents shuttling back and forth so one can feed while the other guards. The riskiest step comes after the chick looks fully grown, when it first has to feed itself at sea. How well that goes depends heavily on ice and food in the ocean, which ties the whole cycle closely to climate.
Courtship and Laying the Eggs
A breeding colony can hold thousands of birds packed onto the same beach or ice patch they used the year before. Many species build nests of stones, burrows or grass, while kings and emperors keep no nest at all. Many pairs reunite with the same partner year after year.
Birds coming back from feeding at sea find their partner in that crowd by listening for its call.1PubMed. Perceptual salience of individually distinctive features in the calls of adult king penguins Some species have no fixed nest to meet at, so voice is the only way to identify each other when they swap duties.2PubMed Central. Penguins use the two-voice system to recognize each other These penguins can sing with two voices at once, and the way the two tones combine carries a personal signature that travels well through a packed crowd of bodies.3PubMed Central. Penguins use the two-voice system to recognize each other
Most penguin species lay a clutch of two eggs, though king and emperor penguins lay just one. Crested penguins such as rockhoppers lay a smaller first egg and a larger second one.4Oxford Academic (The Auk). Egg Temperatures of the Rockhopper Penguin and Some Other Penguins The size of the first egg varies more, and it depends on how long the female spent in the colony before laying.5PubMed Central. Two eggs, two different constraints: a potential explanation for the puzzling intraclutch egg size dimorphism in Eudyptes penguins Heavier females lay eggs with more egg white in both eggs.6PubMed Central. Two eggs, two different constraints: a potential explanation for the puzzling intraclutch egg size dimorphism in Eudyptes penguins
How Penguins Incubate Their Eggs
Parents take turns sitting on the eggs, and one fasts on the egg while the other feeds at sea. In emperor penguins the male alone holds the single egg on his feet through the winter while the female feeds. A breeding male king penguin needs about 0.78 kg of fish a day across the incubation period to cover these shifts.7PubMed. Modeling the marine resources consumed in raising a king penguin chick: an energetics approach
Most species incubate for roughly one to two months. Emperor eggs take about two months, all of it through the Antarctic winter, and a parent can fast for weeks during a single shift.
Heat reaches the egg through a bare area of belly skin with little feather cover. The parent presses the egg against it, and body heat passes straight into the shell. Kings and emperors have no nest, so they balance the egg on their feet under a fold of skin.
At the changeover, the returning parent calls and its partner answers. The egg is carefully passed over, and it is exposed to the cold for a moment during the swap. The relieved bird heads straight to sea to feed.
Eggs are kept warm, but not always at full warmth right away. Late in incubation, eggs sit at about 30 to 34°C in rockhoppers and up to about 36°C in gentoo and African penguins.8Oxford Academic (The Auk). Egg Temperatures of the Rockhopper Penguin and Some Other Penguins Gentoo and African penguin eggs warm above 30°C within a week, while rockhopper eggs take about 16 days.9Oxford Academic (The Auk). Egg Temperatures of the Rockhopper Penguin and Some Other Penguins The smaller first rockhopper egg also runs cooler and less steady than the larger second egg.10Oxford Academic (The Auk). Egg Temperatures of the Rockhopper Penguin and Some Other Penguins
The First Weeks After Hatching
A chick chips through the shell using a small egg tooth on its beak. Hatching can take a day or more, and the chick emerges wet before drying into fluffy down.
Chicks can actively beg for food on their first day.11Journal of Zoology. Behaviour of the yellow‐eyed penguin chick Their eyes open only after three or four days, so at first they beg using touch and sound.12Journal of Zoology. Behaviour of the yellow‐eyed penguin chick Once they can see, begging peaks just after a parent returns to take over.13Journal of Zoology. Behaviour of the yellow‐eyed penguin chick
Parents bring fish, krill or squid back in their stomach and regurgitate the partly digested food into the chick’s mouth. The chick taps or pecks at the parent’s bill to trigger the feeding.
Parents also brood chicks for the first few weeks. Yellow-eyed penguin chicks are kept under a parent for the first 21 to 25 days.14Journal of Zoology. Behaviour of the yellow‐eyed penguin chick African penguin chicks under 20 days old usually lie flat beneath the guarding adult.15Ostrich. BEHAVIOUR OF THE JACKASS PENGUIN CHICK A newly hatched king penguin chick burns energy fast, but its rate drops once its down grows in and insulates it.16PubMed. Energy metabolism of the king penguin chick – Aptenodytes patagonicus (J.F. Miller) – during growth After about three weeks, chicks at open nests can overheat, and on hot days they seek shade and pant.17Journal of Zoology. Behaviour of the yellow‐eyed penguin chick
Siblings mostly share. In yellow-eyed penguins, sibling fighting is mild and both chicks are usually fed at each meal.18Journal of Zoology. Behaviour of the yellow‐eyed penguin chick In species with very unequal eggs, though, the smaller chick often does not survive.
Crèches and Growing Up Fast
Once chicks are big enough, both parents leave to fish and the chicks gather into groups called crèches. These groups protect chicks from aggressive adults, predators and bad weather.19Animal Behaviour. The adaptive significance of crèches in the king penguin In storms, king penguin chicks pack into bigger groups, stand closer together and turn their backs to the wind and rain.20Animal Behaviour. The adaptive significance of crèches in the king penguin African penguin chicks enter this stage at about 26 to 45 days, and feeding then shifts to late afternoon and evening.21Ostrich. BEHAVIOUR OF THE JACKASS PENGUIN CHICK
To be fed, a king penguin chick must pick out its parent’s call over the constant noise of the colony.22Elsevier / Animal Behaviour. Finding a parent in a king penguin colony: the acoustic system of individual recognition Each adult’s call has a distinct pattern in how its pitch rises and falls, and hearing less than a quarter of a second of it is enough for a chick to recognize its parent.23Elsevier / Animal Behaviour. Finding a parent in a king penguin colony: the acoustic system of individual recognition A returning parent calls from the edge of the group, and the chick answers and runs toward it. Parents generally feed only their own chick and push others away.
All this feeding adds up. A king penguin chick needs about 38 kg of fish to reach 8 kg in its first 90 days.24PubMed. Modeling the marine resources consumed in raising a king penguin chick: an energetics approach A breeding male king penguin needs about 1.14 kg of fish a day during that time, more than during incubation.25PubMed. Modeling the marine resources consumed in raising a king penguin chick: an energetics approach
Chicks of small species may leave within two to three months. King penguin chicks stay through winter and take around a year. Over that time the brown or grey down is gradually replaced by waterproof feathers.
Going to Sea for the First Time
Fledging is when a young penguin with adult-like waterproof feathers first heads to sea, and from then on it must feed itself with no parent to help. Young king penguins that had never been to sea all dove past 100 m in their first week.26Journal of Experimental Biology. The early life of king penguins: ontogeny of dive capacity and foraging behaviour in an expert diver Their deepest dives grew from about 118 m in the first week to about 204 m after seven months.27Journal of Experimental Biology. The early life of king penguins: ontogeny of dive capacity and foraging behaviour in an expert diver Still, most of their hunting dives in the first five months stayed shallower than 100 m and under 4 minutes.28Journal of Experimental Biology. The early life of king penguins: ontogeny of dive capacity and foraging behaviour in an expert diver
Young penguins that steadily dove deeper and longer survived their first months at sea.29PubMed Central. Early diving behaviour in juvenile penguins: improvement or selection processes Those whose dives got shallower and shorter over winter likely died.30PubMed Central. Early diving behaviour in juvenile penguins: improvement or selection processes Their deaths most likely came from starvation and cold, sometimes along with predators.31PubMed Central. Early diving behaviour in juvenile penguins: improvement or selection processes Ocean conditions and food supply in the first weeks after fledging also strongly predict whether young emperor penguins survive.32Polar Biology. Intrinsic and extrinsic drivers of juvenile survival in emperor penguins
Leopard seals and orcas wait near colonies for inexperienced birds. Many young penguins do not survive their first year.
Those that do often roam widely and spend years mostly at sea. They may not come back to the colony for a year or more.
The Yearly Molt
Each year, adult penguins replace all their feathers in a few weeks, a process called molting. Without full waterproof feathers they can’t swim, so king penguins fast ashore for about a month.33PubMed. Energy and protein requirements for molt in the king penguin Aptenodytes patagonicus By the end of molt they have lost about 44% of their starting body weight.34PubMed. Energy and protein requirements for molt in the king penguin Aptenodytes patagonicus The old feathers drop out between about days 12 and 21.35PubMed. Energy and protein requirements for molt in the king penguin Aptenodytes patagonicus
A molting penguin looks ragged, puffed out and patchy. It stands still and hunched to save energy. Molting adults are healthy, not sick, and young birds go through their first adult molt after a year or so.
Penguins prepare at sea. About 18% of the new feathers start growing while the penguin is still at sea, which shortens the fast and lowers what the body has to supply.36PubMed. Energy and protein requirements for molt in the king penguin Aptenodytes patagonicus The body burns more energy while molting than during a breeding fast.37PubMed. Energy and protein requirements for molt in the king penguin Aptenodytes patagonicus Building feathers uses protein, so the body breaks down twice as much muscle and other protein as in a breeding fast.38PubMed. Energy and protein requirements for molt in the king penguin Aptenodytes patagonicus
Fat matters just as much. Penguins feed heavily beforehand to build reserves, and fat supplies most of the energy for the fast. A bird that runs too low may not survive it.
Becoming a Breeding Adult
Little penguins can breed at about 2 to 3 years, while large species such as emperors usually start around 5 or later. Early growth plays a part. Little penguins that grew slowly as chicks were less likely to breed at age 2, about 29% compared with up to 67% for other chicks.39PubMed Central. Early‐growth trajectories affect juvenile survival, age at first reproduction and lifetime fitness in a long‐lived seabird, the little penguin
Breeding also improves with practice. An Adélie penguin’s first breeding attempt is its least successful, whatever its age.40PubMed. Age-related reproductive performance of the Adélie penguin, a long-lived seabird exhibiting similar outcomes regardless of individual life-history strategy Success then improves with early experience.41PubMed. Age-related reproductive performance of the Adélie penguin, a long-lived seabird exhibiting similar outcomes regardless of individual life-history strategy Adélies that start breeding older have higher success from the start, but starting at different ages did not change the total number of breeding attempts over a lifetime.42PubMed. Age-related reproductive performance of the Adélie penguin, a long-lived seabird exhibiting similar outcomes regardless of individual life-history strategy
Many penguins live 15 to 20 years in the wild. Most species breed once a year, though king penguins can raise at most two chicks every three years because their chick period is so long.
What Threatens Each Stage of the Cycle
Ice and food drive breeding success. In 2022, record low Antarctic sea ice caused total breeding failure at four of five emperor colonies in one region.43Communications Earth & Environment. Record low 2022 Antarctic sea ice led to catastrophic breeding failure of emperor penguins The ice broke up before chicks had grown waterproof feathers.44Communications Earth & Environment. Record low 2022 Antarctic sea ice led to catastrophic breeding failure of emperor penguins When Adélie parents must travel farther to the ice edge to feed, fewer chicks survive, and heavy May snowfall can reduce how many Adélie eggs hatch.45PubMed Central. Landfast ice: a major driver of reproductive success in a polar seabird In years with less food, royal penguins lay their eggs later.46PubMed Central. Long-term breeding phenology shift in royal penguins
Climate change fits in because penguins time breeding to seasons of ice and food. Warming shifts when and where both are available, and species tied to sea ice, like emperors, are most at risk.
People can disturb colonies too. At Adélie colonies with tourist visits, hatching success was 47% lower and chick survival 80% lower than at undisturbed colonies.47Elsevier / Biological Conservation. Effects of human activity on adelie penguin Pygoscelis adeliae breeding success If you visit, keep well back from nesting penguins and follow wildlife-viewing rules.