Emperor Penguin Eating: Their Diet and Hunting Methods

Emperor penguins feed primarily on fish, with Antarctic silverfish making up the bulk of their diet, supplemented by squid and krill in proportions that shift with the season. What makes their feeding remarkable is not just what they eat but how they get it: hunting beneath Antarctic sea ice in near-total darkness, diving to depths that would crush most other birds, and traveling hundreds of kilometers from their colonies to reach open water. Their entire physiology, from their eyes to their blood chemistry to their muscles, is shaped around the demands of catching prey in one of Earth’s most extreme environments.

What Emperor Penguins Actually Eat

Antarctic silverfish dominate the emperor penguin diet, particularly during the chick-rearing season when adults are bringing food back to the colony. At two major colonies in the Ross Sea, silverfish accounted for about three-quarters of the food delivered to chicks, representing roughly 76 percent at Cape Washington and 73 percent at Coulman Island.¹ These small, ice-associated fish are abundant in Antarctic waters and pack a high energy density relative to their size, making them an efficient food source for a bird that may need to travel long distances between feeding grounds and its colony.

Squid and krill fill in the rest of the diet. Squid tend to be caught during deeper dives, and their beaks often show up in stomach content analyses because they resist digestion longer than soft fish tissue. Krill become more prominent in the diet during summer, when sea ice retreats and krill swarms become more accessible in open water.² The balance between fish, squid, and krill is not fixed; it shifts depending on what is available, and emperor penguins are more flexible in their diet than researchers once assumed.

How the Diet Shifts with Season and Sea Ice

For years, the emperor penguin was treated as a relatively specialized fish-eater. Newer research using stable isotope analysis of feathers, blood, and guano has revealed a more dynamic picture. The relative contributions of fish and krill to the diet change not just between seasons but between breeding stages.² During winter, when extensive sea ice locks up much of the ocean surface and krill are harder to reach, fish dominate. In summer, krill consumption rises substantially.

These shifts track with sea ice dynamics. When fast ice extends far from the coast, penguins must travel farther to find open leads or polynyas where prey congregates. The prey assemblage near these openings tends to be fish-heavy in winter and more mixed in summer, and the penguins’ diet reflects that. This “trophic plasticity,” as researchers describe it, had not been widely recognized in emperor penguins before isotopic studies revealed it, even though the closely related Adélie penguin was already known to be a flexible feeder.

Diving Depths and Durations

Emperor penguins are the deepest-diving birds on Earth. Studies of breeding birds at Coulman Island recorded dives as deep as 534 meters and as long as 15.8 minutes.³ Those are extremes, though. The typical foraging dive is far shallower and shorter. Modal foraging depth fell between 21 and 40 meters, with most dives lasting four to five minutes.³

Dive timing follows a clear pattern. Shallow dives under 200 meters happen around the clock, but the really deep dives, those exceeding 400 meters, are concentrated between roughly 5 a.m. and 7 p.m.³ This makes sense when you consider that deeper water is darker, and even the emperor penguin’s remarkable visual system has limits. The deepest dives occur when at least some ambient light can penetrate from above, improving the bird’s ability to spot and intercept prey at depth.

The shallow modal dive depth is worth pausing on, because it tells us something about hunting strategy. Emperor penguins are capable of extraordinary dives, but they do not use them routinely. Most feeding happens in relatively shallow water under or near sea ice, where silverfish aggregate. The deep dives likely represent forays after squid or fish that live in midwater, not the bread-and-butter hunting that sustains the colony.

How Their Bodies Handle the Pressure

A five-minute dive to 40 meters is demanding enough, but the emperor penguin’s physiology is built to handle far more. The key bottleneck in any dive is oxygen: how much the animal stores before submerging, how efficiently it parcels that oxygen out during the dive, and what happens when it runs low.

Emperor penguins carry oxygen in three compartments: the lungs, the blood, and the muscles. Their myoglobin, the oxygen-storing protein in muscle, is adapted to Antarctic conditions in ways that matter for sustained diving. The protein’s oxygen-binding properties work well at low temperatures, and importantly, the buildup of lactate (a byproduct of anaerobic exertion) does not impair myoglobin function even during prolonged physical effort.⁴ This means the muscle oxygen reservoir keeps working even when the bird is pushing into anaerobic territory near the end of a long dive.

Researchers have identified two distinct physiological strategies that emperor penguins use during dives. In some dives, muscle oxygen drops steadily from start to finish, consistent with the muscles operating on their stored oxygen with minimal blood flow from the rest of the body. In other dives, muscle oxygen drops more gradually and may plateau mid-dive, suggesting the bird is maintaining some blood flow to the muscles and parceling out oxygen more evenly.⁵ Both strategies end the same way on long dives: muscle oxygen is nearly completely depleted by the time the bird surfaces.⁶

The practical upshot is that emperor penguins can adjust how they burn through their oxygen reserves depending on what the dive demands. A short, fast chase after a fleeing fish might favor the rapid-depletion strategy. A longer, slower search through midwater might favor the gradual approach. Either way, when the oxygen runs out, lactate begins accumulating, and the bird needs to surface and recover before diving again.

Eyes Built for Hunting in the Dark

Hunting beneath Antarctic sea ice means hunting in dim conditions, sometimes in near-darkness. Emperor penguins have visual adaptations that set them apart from shallower-diving penguin species. Their retinas are rod-dominated, which favors sensitivity to low light levels over sharp color vision. They also have pale oil droplets in their photoreceptors, a feature seen in other deep-diving penguins but not in their shallow-diving relatives.⁷ These oil droplets act as filters, and pale droplets let more light through to the photoreceptor, further boosting sensitivity in dark water.

At the molecular level, something even more interesting is going on. The rhodopsin protein in emperor penguin eyes, the primary light-detecting pigment used in dim conditions, has undergone a specific mutation that speeds up how quickly the pigment recharges after absorbing a photon. This same mutation has evolved independently in deep-diving mammals like beaked whales, a striking example of convergent evolution driven by the shared challenge of seeing in deep, dark water.⁸ Faster rhodopsin recharging means the eye can adjust more quickly to changing light levels as the penguin descends through the water column, where light intensity drops dramatically with each additional meter of depth.

A single amino acid change in the rhodopsin protein accounts for the increased recharging speed in both emperor penguins and beaked whales.⁸ That such distantly related animals arrived at the same molecular solution independently speaks to how strongly the deep-ocean environment selects for low-light vision.

Vocalizations During the Hunt

One of the more unexpected findings in penguin biology is that some species vocalize underwater while hunting. Research deploying cameras and accelerometers on king penguins and gentoo penguins recorded short vocalizations during feeding dives, mostly during the bottom phase of the dive when the birds were actively pursuing prey.⁹ More than half of the recorded calls were directly associated with hunting behavior: they followed an acceleration (likely a chase) or immediately preceded a prey capture attempt. The calls were extremely brief, averaging about 0.06 seconds each.

This research was conducted on king and gentoo penguins, not emperors, so it is not certain that emperor penguins use the same behavior. But the king penguin is the emperor’s closest living relative, and the two share many foraging strategies. If king penguins are vocalizing to startle, disorient, or herd prey during dives, it would be surprising if emperor penguins had not evolved something similar. Confirming this will require deploying the same kind of recording equipment on free-diving emperor penguins, which is logistically harder given the more remote and extreme conditions of their breeding and foraging habitat.

How Far They Travel to Feed

Emperor penguins do not feed near their colonies. The colonies sit on fast ice attached to the coast, often dozens or hundreds of kilometers from open water. Getting to food requires serious travel. Satellite tracking of birds in West Antarctica recorded foraging trips lasting about 10 days on average, with penguins reaching maximum distances of roughly 75 kilometers from the colony within coastal waters.¹⁰ These birds generally stayed within 100 kilometers of land and within 5 to 10 kilometers of features like open water patches, polynyas, leads, and icebergs that offered access to the ocean.

But those numbers reflect chick-rearing trips from one region. Outside the breeding season, distances can be much greater. Satellite tracking in earlier studies documented winter birds walking over fast ice as far as 296 kilometers to feed at polynyas, while birds swimming through lighter pack ice traveled as far as 895 kilometers from the breeding colony.¹¹ That range is astonishing for a flightless bird and reflects the harsh reality of Antarctic geography: food and nesting sites are separated by vast expanses of ice.

Traveling speed also changes with context. Tracked penguins in West Antarctica moved at about 2.3 kilometers per hour during foraging trips, then slowed to about 0.8 kilometers per hour during the moult period, when they hauled out on sea ice and were largely drifting with the ice rather than actively traveling.¹⁰

Preserving Food in the Stomach

Emperor penguins face a problem that most predators do not: one parent must fast at the colony while the other forages, and the foraging parent may need to store food in its stomach for weeks before feeding it to a chick. Male emperor penguins famously incubate the egg through the Antarctic winter while the female is at sea, and when the chick hatches, the male has to feed it from whatever remains in his stomach. The food needs to still be nutritious after sitting there for days or weeks.

Remarkably, prey stored in the stomach for up to 20 days was found to be in a similar physical state of preservation as food in birds that had just returned from the sea. Fish remains were mashed up and squid parts were still intact.¹² The stomach appears to act as a kind of natural refrigerator, suppressing digestion and bacterial decomposition. The mechanism likely involves antimicrobial compounds in the stomach lining, combined with low body temperature during the fasting period and reduced gastric acid secretion.

The composition of the stored food does change, though. The proportion of lipid in the stomach contents dropped from about 24 percent in newly returned birds to about 17 percent in birds that had been fasting at the colony, while protein content rose from roughly 57 percent to 69 percent.¹² The birds appear to be selectively absorbing some of the fat for their own energy needs while preserving the protein-rich portion for the chick. It is an elegant bit of metabolic triage: the adult gets the fuel it needs most (fat, for warmth and survival), and the chick gets protein for growth.

The Fasting Cycle and the Signal to Stop

Emperor penguins endure some of the longest fasts in the bird world. Males may go without food for over 100 days during courtship, egg-laying, and incubation, relying on fat reserves built up during pre-breeding feeding bouts. During most of this fast, the body burns almost entirely fat, sparing protein to protect muscle and organ function.¹³

But there is a limit. When fat reserves drop below a critical threshold, the body begins breaking down protein for energy at a much higher rate. This metabolic shift triggers a cascade of behavioral and hormonal changes that researchers call the “refeeding signal.” In captive studies, when fasting emperor penguins dropped below a body mass of roughly 24 kilograms, their spontaneous activity increased up to eightfold, escape attempts jumped fifteenfold, and they resumed display songs, all signs of a dramatically increased drive to leave and find food.¹⁴

Hormonally, the shift involves rising levels of corticosterone (a stress hormone) and falling levels of prolactin (the hormone associated with brooding behavior).¹³ In practical terms, the bird’s body chemistry shifts from “stay and protect the egg” to “leave now or die.” In the wild, birds reaching this stage begin leaving the egg unattended for longer and longer periods before eventually abandoning it to go feed. The signal is calibrated to fire before the bird reaches lethal depletion, giving it enough remaining energy to make the trek back to open water.

This system exists because emperor penguins breed under conditions where the nearest food is hundreds of kilometers away, and no individual can afford to starve to death on the ice. Egg abandonment is costly, but it is less costly than losing both the egg and the adult. The threshold body mass of about 24 kilograms represents roughly a 40 percent loss from the pre-fast body weight of a typical male, which enters incubation at around 38 to 40 kilograms.

Tracking Technology and What We Still Cannot See

Much of what we know about emperor penguin foraging comes from biologging: instruments attached to the birds that record depth, speed, acceleration, location, and sometimes video. The technology has improved enormously over the past two decades. Early studies relied on simple time-depth recorders that told you how deep a bird went and for how long, but nothing about what happened at depth. Modern accelerometers can detect the rapid head movements associated with individual prey captures, and when paired with cameras, researchers can match acceleration signatures to actual feeding events.

This integrated approach was demonstrated in a study of Adélie penguins, where head-mounted accelerometers successfully detected prey captures with high accuracy when validated against simultaneous video footage.¹⁵ That study found remarkably fast capture rates: two krill per second in dense swarms. While those numbers apply to Adélie penguins rather than emperors, the methodology is now being applied across penguin species, and it opens the door to understanding not just where emperor penguins dive but exactly how many prey items they catch per dive and how capture efficiency varies with depth, light, and prey type.

The limitations of biologging are real, though. Cameras record for only about 85 minutes at a stretch, which captures only a handful of dives. Accelerometers last much longer, around 50 hours in that Adélie study, but without video validation they can miss unusual prey capture behaviors or confuse prey catches with other rapid movements. And all of these instruments add weight and drag to the bird, potentially altering the very behavior they are meant to record. Researchers are working on smaller, lighter devices, but emperor penguin foraging studies remain logistically grueling because the birds breed in some of the most inaccessible places on the continent, during the worst weather on Earth.