The king penguin (Aptenodytes patagonicus) is a large species of penguin, second only to the emperor penguin in size. There are two subspecies: A. p. patagonicus and A. p. halli; patagonicus is found in the South Atlantic and halli found at the Kerguelen Islands and Crozet Island, Prince Edward Islands, Heard Island and McDonald Islands, and Macquarie Island.
King penguins eat small fish, mainly lanternfish, and squid. They are less reliant on krill and other crustaceans than most Southern Ocean predators. On foraging trips king penguins repeatedly dive to over 100 meters (300 ft), and have been recorded at depths greater than 300 metres (1,000 ft).
King penguins breed on the subantarctic islands at the northern reaches of Antarctica, South Georgia, and other temperate islands of the region. King penguins do not live or breed in Westarctica.
The king penguin stands at 70 to 100 cm (28 to 39 in) tall and weighs from 9.3 to 18 kg (21 to 40 lb). Males are slightly larger than females. The mean body mass of adults from Marion Island was 12.4 kg (27 lb) for 70 males and 11.1 kg (24 lb) for 71 females. Another study from Marion Island found that the mean mass of 33 adults feeding chicks was 13.1 kg (29 lb). Thus the average weight of the king penguin is similar or just slightly higher than that of the largest living flying birds.
The plumage of the king penguin is broadly similar to that of the closely related emperor penguin, with a broad cheek patch contrasting with surrounding dark feathers and yellow-orange color at the top of the chest. However, the cheek patch of the adult king penguin is bright orange whereas that of the emperor penguins is white, while the chest orange tends to be more vivid and less yellowish in the king species. Both species have colorful markings along the side of their lower mandible, but these are pinkish in emperor penguins and orange in king penguins. Emperor and king penguins typically do not occur together in the wild, with the possible exception of vagrants at sea, but the emperor can readily be distinguished by being noticeably larger and bulkier. Once fully molted of its heavy dark brown down, the juvenile king penguin resembles the adult but is somewhat less colorful.
King penguins often breed on the same large, circumpolar islands as at least half of all living penguins, but it is easily distinguished from co-occurring penguins by its much larger size and taller frame, distinctive markings and grizzled sooty-grayish rather than blackish back.
American zoologist Gerry Kooyman revolutionized the study of penguin foraging behavior in 1971 when he published his results from attaching automatic dive-recording devices to emperor penguins, and recording a dive of 235 meters (771 ft) by a king penguin in 1982. The current maximum dive recorded is 343 meters in the Falkland Islands region, and a maximum time submerged of 552 seconds recorded at the Crozet Islands. The king penguin dives to depths of 100–300 meters (350–1000 feet), spending around five minutes submerged, during daylight hours, and less than 30 meters (98 ft) at night.
The majority (around 88% in one study) of dives undertaken by king penguins are flat-bottomed; that is, the penguin dives to a certain depth and remains there for a period of time hunting (roughly 50% of total dive time) before returning to the surface. They have been described as U-shaped or W-shaped, relating to the course of the dive. The remaining 12% of dives have a V-shaped or "spike" pattern, in which the bird dives at an angle through the water column, reaches a certain depth, and then returns to the surface. In contrast, other penguins dive in this latter foraging pattern. Observations at Crozet Islands revealed most king penguins were seen within 30 km (19 mi) of the colony. Using the average swimming speed, Kooyman estimated the distance traveled to foraging areas at 28 km (17 mi).
The king penguin's average swimming speed is 6.5–10 km/h (4–6 mph). On shallower dives under 60 m (200 ft), it averages 2 km/h (1.2 mph) descending and ascending, while on deeper dives over 150 m (490 ft) deep, it averages 5 km/h (3.1 mph) in both directions. King penguins also "porpoise," a swimming technique used to breathe while maintaining speed. On land, the king penguin alternates between walking with a wobbling gait and tobogganing—sliding over the ice on its belly, propelled by its feet and wing-like flippers. Like all penguins, it is flightless.