Emperor Penguin

The emperor penguin is a social animal in its nesting and its foraging behaviour; birds hunting together may coordinate their diving and surfacing. Individuals may be active day or night. A mature adult travels throughout most of the year between the breeding colony and ocean foraging areas; the species disperses into the oceans from January to March. The American physiologist Gerry Kooyman revolutionised the study of penguin foraging behaviour in 1971 when he published his results from attaching automatic dive-recording devices to emperor penguins. He found that the species reaches depths of 265 m (869 ft), with dive periods of up to 18 minutes. Later research revealed a small female had dived to a depth of 535 m (1,755 ft) near McMurdo Sound. It is possible that emperor penguins can dive for even deeper and longer periods, as the accuracy of the recording devices is diminished at greater depths. Further study of one bird's diving behaviour revealed regular dives to 150 m (490 ft) in water around 900 m (3,000 ft) deep, and shallow dives of less than 50 m (160 ft), interspersed with deep dives of more than 400 m (1,300 ft) in depths of 450 to 500 m (1,480 to 1,640 ft). This was suggestive of feeding near or at the sea bottom. In 1994, a penguin from Auster rookery reached a depth of 564 m; entire this dive took him 21.8 min. Both male and female emperor penguins forage for food up to 500 km (311 mi) from colonies while collecting food to feed chicks, covering 82–1,454 km (51–903 mi) per individual per trip. 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. An efficient swimmer, the emperor penguin exerts pressure with both its upward and downward strokes while swimming. The upward stroke works against buoyancy and helps maintain depth. Its average swimming speed is 6–9 km/h (3.7–5.6 mph). 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. Like all penguins, it is flightless. The emperor penguin is a very powerful bird. In one case, a crew of six men, trying to capture a single male penguin for a zoo collection, were repeatedly tossed around and knocked over before all of the men had to collectively tackle the bird, which weighs about half as much as a man. As a defence against the cold, a colony of emperor penguins forms a compact huddle (also known as the turtle formation) ranging in size from ten to several hundred birds, with each bird leaning forward on a neighbour. As the wind chill is the least severe in the center of the colony, all the juveniles are usually huddled there. Those on the outside upwind tend to shuffle slowly around the edge of the formation and add themselves to its leeward edge, producing a slow churning action, and giving each bird a turn on the inside and on the outside.

The emperor penguin has a circumpolar distribution in the Antarctic almost exclusively between the 66° and 77° south latitudes. It almost always breeds on stable pack ice near the coast and up to 18 km (11 mi) offshore. Breeding colonies are usually in areas where ice cliffs and icebergs provide some protection from the wind. Three land colonies have been reported: one (now disappeared) on a shingle spit at the Dion Islands on the Antarctic Peninsula, one on a headland at Taylor Glacier in Victoria Land, and most recently one at Amundsen Bay. Since 2009, a number of colonies have been reported on shelf ice rather than sea ice, in some cases moving to the shelf in years when sea ice forms late. The northernmost breeding population is on Snow Island, near the northern tip of the Peninsula. Individual vagrants have been seen on Heard Island, South Georgia, and occasionally in New Zealand. The total population was estimated in 2009 to be at around 595,000 adult birds, in 46 known colonies spread around the Antarctic and sub-Antarctic; around 35% of the known population lives north of the Antarctic Circle. Major breeding colonies were located at Cape Washington, Coulman Island in Victoria Land, Halley Bay, Cape Colbeck, and Dibble Glacier. Colonies are known to fluctuate over time, often breaking into "suburbs" which move apart from the parent group, and some have been known to disappear entirely. The Cape Crozier colony on the Ross Sea shrank drastically between the first visits by the Discovery Expedition in 1902–03 and the later visits by the Terra Nova Expedition in 1910–11; it was reduced to a few hundred birds, and may have come close to extinction due to changes in the position of the ice shelf. By the 1960s it had rebounded dramatically, but by 2009 was again reduced to a small population of around 300.

In 2012 the emperor penguin was uplisted from a species of least concern to near threatened by the IUCN. Along with nine other species of penguin, it is currently under consideration for inclusion under the US Endangered Species Act. 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. Other reasons for the species's placement on the Endangered Species Act's list include disease, habitat destruction, and disturbance at breeding colonies by humans. Of particular concern is the impact of tourism. One study concluded that emperor penguin chicks in a crèche become more apprehensive following a helicopter approach to 1,000 m (3,300 ft). 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. On the other hand, egg hatching success rates declined when the sea-ice extent increased; chick deaths also increased; The species is therefore considered to be highly sensitive to climatic changes. 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. This was the first confirmed loss of an entire colony. 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. However, this increase is nowhere near the total number of breeding adults formerly at the Halley Bay colony. A Woods Hole Oceanographic Institution study in January 2009 found that emperor penguins could be pushed to the brink of extinction by the year 2100 due to global climate change. 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. The study forecasted an 87% decline in the colony's population, from three thousand breeding pairs in 2009 to four hundred breeding pairs in 2100. In June 2014 a study by the Woods Hole Oceanographic Institution concluded that emperor penguins are at risk from global warming, which is melting the sea ice. This study predicted that by 2100 all 45 colonies of emperor penguins will be declining in numbers, mostly due to loss of habitat. Loss of ice reduces the supply of krill, which is a primary food for emperor penguins.