Feathers of the head and back are black and sharply delineated from the white belly, pale-yellow breast and bright-yellow ear patches.

Emperor penguins were described in 1844 by English zoologist George Robert Gray, who created the generic name from Ancient Greek word elements, ἀ-πτηνο-δύτης [a-ptēno-dytēs], "without-wings-diver".

Ksepka et al. (2012) measured standing height of 81–94 cm (32–37 in) according to 11 complete skins collected in American Museum of Natural History.

[10] The weight also varies by season, as both male and female penguins lose substantial mass while raising hatchlings and incubating their egg.

[21] As the species has no fixed nesting sites that individuals can use to locate their own partner or chick, emperor penguins must rely on vocal sounds alone for identification.

[33] In addition to the cold, the emperor penguin encounters another stressful condition on deep dives—markedly increased pressure of up to 40 times that of the surface, which in most other terrestrial organisms would cause barotrauma.

[42] This individual, which is believed to have originated from eastern Antarctica, was encountered by a group of surfers shortly after it arrived in Denmark, and was taken in by conservationists at the Department of Biodiversity, Conservation and Attractions to have its condition evaluated.

The primary causes for an increased risk of species endangerment are declining food availability, due to the effects of climate change and industrial fisheries on the crustacean and fish populations.

Population declines of 50% in the Terre Adélie region have been observed due to an increased death rate among adult birds, especially males, during an abnormally prolonged warm period in the late 1970s, which resulted in reduced sea-ice coverage.

[50] In 2009, the Dion Islands colony, which had been extensively studied since 1948, was reported to have completely disappeared at some point over the previous decade, the fate of the birds unknown.

[51] Beginning in September 2015, a strong El Niño, strong winds, and record low amounts of sea ice resulted in "almost total breeding failure" with the deaths of thousands of emperor chicks for three consecutive years within the Halley Bay colony, the second largest emperor penguin colony in the world.

Researchers have attributed this loss to immigration of breeding penguins to the Dawson-Lambton colony 55 km (34 mi) south, in which a tenfold population increase was observed between 2016 and 2018.

[52] In January 2009, a study from the Woods Hole Oceanographic Institution concluded that global climate change could push the emperor penguin to the brink of extinction by the year 2100.

The study constructed a mathematical model to predict how the loss of sea ice from climate warming would affect a big colony of emperor penguins at Terre Adélie, Antarctica.

[53] Another study by the Woods Hole Oceanographic Institution in 2014 again concluded that emperor penguins are at risk from global warming, which is melting the sea ice.

[55] In 2023, another study found that more than 90% of emperor penguin colonies could face "quasi-extinction" from "catastrophic breeding failure" due to the loss of sea ice caused by climate change.

A male returning to the sea after incubation heads directly out to areas of permanent open water, known as polynyas, around 100 km (62 mi) from the colony.

[64] On land, the emperor 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.

[19] The yearly reproductive cycle begins at the start of the Antarctic winter, in March and April, when all mature emperor penguins travel to colonial nesting areas, often walking 50 to 120 km (31 to 75 mi) inland from the edge of the pack ice.

[77] After laying, the mother's food reserves are exhausted and she very carefully transfers the egg to the male, and then immediately returns to the sea for two months to feed.

[81] The chick usually hatches before the mother's return, and the father feeds it a curd-like substance composed of 59% protein and 28% lipid, which is produced by a gland in his oesophagus.

Research indicates that between 10-20% of female Emperor penguins do not return to their colony from foraging at sea, most victims of the harsh winter weather conditions or being eaten by predators.

[71] She finds her mate among the hundreds of fathers by his vocal call and takes over caring for the chick, feeding it by regurgitating the partially digested fish, squid and krill that she has stored in her stomach.

The male is often reluctant to surrender the chick he has been caring for all winter to its mother, but he soon leaves to take his turn at sea, spending 3 to 4 weeks feeding there before returning.

[81] A crèche may consist of around a dozen, up to several thousand chicks densely packed together and is essential for surviving the low Antarctic temperatures.

[87] From early November, chicks begin moulting into juvenile plumage, which takes up to two months and is usually not completed by the time they leave the colony.

Malcolm Davis of the National Zoological Park made early attempts at keeping penguins, capturing several from Antarctica.

[98] Since then it has been kept and bred at a few other facilities in China, and the only confirmed twin emperor penguins (the species normally lays just one egg) hatched at Sun Asia Ocean World in Dalian in 2017.

He had consumed 3 kg (6.6 lb) of sand, which he had apparently mistaken for snow, as well as sticks and stones, and had to undergo a number of operations to remove these to save his life.

Following recovery, on 4 September, the juvenile, named "Happy Feet" (after the 2006 film), was fitted with a tracking device and released into the Southern Ocean 80 km (50 mi) north of Campbell Island.