The Emperor penguin (scientific name: Aptenodytes forsteri G. R. Gray, 1844) is one of seventeen species of flightless birds in the family of penguins, and with the King penguin forms the genus Aptenodytes or "Great penguins".
Like all penguins, the Emperor penguin is characterized by its erect posture, stiff wings, excellent swimming ability, awkward movement out of water, and coloring. The black back and white front, make penguins difficult to see when swimming, blending against the sea from above and the sky from below.
Emperor penguins are strikingly colored, with deep black feathers dorsally, including the head, chin, throat, back, dorsal part of the wings (flippers), and tail. This dark coloration fades to a brownish color as it becomes worn, between December and February. The belly is satin white from the upper breast to venter and including the underparts of the wings. Auricular patches are bright yellow at the head, fading to a less vivid yellow as the patch meets the white breast feathers. The upper mandible is black and the lower mandible is pink, orange, or lilac colored. Males and females are similar in size and coloration throughout the year. Immature Emperor penguins are similar in size and coloration to adults, except that their auricular patches, chin, and throat are white. Chicks are covered with silvery-grey downy feathers with a black head and distinctive white eye and cheek patches. Adults weigh from 22 to 37 kg, depending on where they are in the reproductive cycle, as both males and females lose substantial portions of their mass while incubating eggs and tending to hatchlings. They stand up to about 115 cm.
Emperor penguins travel to colonial nesting areas in March to early April, when pair formation and breeding occurs.
Emperor penguins are monogamous during each breeding season. Although most individuals form a new pair bond with a new individual each year, one study found that 14.6% of pairs in one year were re-formed the next year, and 4.9% in the third year. Males arrive at the nesting site shortly before females and begin to display to attract females. There is an unequal sex ratio in Emperor penguins, with more females than males (at one site 39.5% males, 60.5% females). This unequal sex ratio leads to intense competition for mates among females. Males use the "ecstatic" display to attract females - in which they stand still, let the head fall to the chest, inhales, gives a courtship call, and holds his position for a few seconds before moving on to another position. Courtship calls are characterized by repeated syllables separated by silent periods, and are performed by both sexes. Calls are highly variable among individuals and serve a critical role in individual recognition.
In May or early June a single, large (460 to 470 g) egg is laid and is passed from the female parent's feet to the male parent's feet for incubation. Females then return to their foraging areas until the end of incubation. All egg laying and hatching is highly synchronous in colonies. Parental protection of eggs and hatchlings is critical, as incubation and brooding occurs during the depths of the Antarctic winter in some of the most severe and frigid conditions on earth. Exposure of eggs and hatchlings to the cold can result in rapid death. Chicks grow rapidly , fledgling at about 50% of adult mass. Most Emperor penguins make their first return to the nesting colony at about 4 years old, but age at first breeding is usually 5 to 6 years in males and 5 years in females.
Males are solely responsible for incubating the eggs, a period of about 64 days. Females invest significant portions of energy into egg laying and leave to forage soon after. When the eggs begin to hatch, females return to take over brooding and feeding of the hatchling. Males can feed the hatchlings with an esophageal secretion for up to 10 days after hatching, if the female hasn't returned. At this point males have been fasting for about 115 days. Males and females then alternate brooding responsibilities with foraging trips for 45 to 50 days after hatching. Males and females regurgitate food for the young from these foraging trips. As the chicks grow the frequency of foraging trips by both parents increases, as the area of open water comes closer to the colony during the Antarctic summer. Young Emperor penguins then form large creches of chicks until they leave the nesting area, at about 150 days old, in December to early January. At this point they have been abandoned by their parents and have not yet begun to molt their downy feathers. By the time they reach open water foraging areas they have nearly completed their molt.
Average longevity for Emperor penguins has been estimated at 19.9 years. At least 19.1% of young survive their first year and 95.1% of adults are estimated to survive from year to year.
Emperor penguins are social animals, both foraging and nesting in groups. Nesting occurs in large colonies, where only small areas around individuals are defended during good weather. In severe weather individuals huddle together for protection. They may be active at any time of the day or night. Reproducing adults travel throughout most of the year between the nesting area and foraging areas in the ocean. All Emperor penguins disperse into the oceans from January to March each year, traveling and foraging in groups. Emperor penguins are excellent swimmers, reaching speeds up to 3.4 meters per second. On land they move with a shuffling gait or propel themselves along the ground by pushing with their feet and sliding on their bellies. During the beginning of the Antarctic winter, in March and April, all mature Emperor penguins travel to colonial nesting areas, often walking 50 to 120 km from the edge of the pack ice.
Emperor penguins do not maintain home ranges.
Emperor penguins use a complex set of vocalizations that are critical in individual recognition between mates and parents and offspring. Their calls are known for using two frequency bands simultaneously, a "two-voice" system. Aside from the mate attraction and recognition calls described above, Emperor penguins use contact calls to maintain contact with conspecifics during feeding or travel. Chicks use a frequency-modulated whistle to beg for food and to contact a parent. Physical displays are also used to communicate among conspecifics. An appeasement posture, where the flippers are held slightly out and the bill is raised, is used to avoid aggression when moving through the colony. It is unknown how Emperor penguins perceive prey, as they can dive to depths of 400 to 450 meters in pursuit of prey, depths at which there is little to no light.
Emperor penguins are restricted to the cold waters of the Antarctic. Their terrestrial range is limited to the fast ice, continental shelf, and surrounding islands between 66 and 78 degrees south latitude.
Emperor penguins forage exclusively in the cold waters of the Antarctic, with rare individuals being found further north than 65 degrees South. They breed almost exclusively on stable pack ice near coastal areas and up to 18 km offshore. Only two, small breeding colonies are known to occur on land. Breeding colonies usually occur in sheltered areas, where ice cliffs and icebergs protect the site from the harshest of winds.
Antarctic giant petrels (Macronectes giganteus) and Antarctic skuas (Catharacta maccormicki) are the primary predators of chicks in colonies, taking from 7% to 34% of young. Leopard seals (Hydrurga leptonyx) take young when they enter the sea after moulting and adults (0.5% of breeding population during November and December in one study). Adults are also taken by killer whales (Orca orcinus). Little is known about specific anti-predatory adaptations, although Emperor penguins probably use their speed and agility in the water to escape some predation and may be warned of predators by group members.
Emperor penguins are important members of the Antarctic ecosystem. They are predators of small Actinopterygii, Cephalopoda, and Crustacea and are, in turn, important prey for larger predators such as leopard seals (Hydrurga leptonyx) and large Chondrichthyes.
Emperor penguins eat primarily Crustacea, Actinopterygii, and Cephalopoda. The proportions of prey they take vary seasonally and geographically, depending on the abundance of prey in the area. Crustaceans eaten are primarily amphipods (Amphipoda) or from the family Euphausiidae (krill), making up to 75% of the diet in some areas. Cephalopods eaten include Psychroteuthis glacialis, Alluroteuthis antarcticus, and Kondakovia longimana. Fish prey include Gymndraco acuticeps, Pleuragramma antarcticum, Trematomus eulepidotus, other Trematomus species, Pagothenia species, Notolepis coatsi, Electrona antarctica, and fish in the family Channichthyidae.
Emperor penguins search for prey in the open water of the Southern Ocean or in ice-free polynyas (an area of open water) and tidal cracks in pack ice. They have been recorded diving to depths of 400 to 450 meters and traveling 150 to 1000 km in a single foraging trip.
Emperor penguins are not considered endangered and are not currently protected under international or regional laws. In areas where reliable population counts have been conducted, the evidence suggests that populations are stable. However, some colonies have not been monitored consistently and human disturbance may result in declines in breeding populations. Estimates of population sizes (as of 1995) were 195,400 breeding pairs, or a total population size of 400,000 to 450,000.
Research on the extraordinary abilities of Emperor penguins to withstand extreme cold, and to successfully reproduce under those conditions, can help humans to understand and appreciate the evolution of these incredible adaptations.
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