Jump to content

Emperor penguin

Page semi-protected
From Wikipedia, the free encyclopedia

This is an old revision of this page, as edited by Jimfbleak (talk | contribs) at 06:19, 20 March 2008 (→Vocalization). The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.

Emperor Penguin
Scientific classification
Kingdom:
Animalia
Phylum:
Chordata
Class:
Aves
Order:
Sphenisciformes
Family:
Spheniscidae
Genus:
Aptenodytes
Species:
A. forsteri
Binomial name
Aptenodytes forsteri
Emperor Penguin range
Breeding colonies in green

The Emperor Penguin (Aptenodytes forsteri) is the tallest and heaviest of all living penguin species and endemic to Antarctica. The male and female are similar in plumage and size, reaching 122 cm (48 in) in height and weighing anywhere from 22 to 37 kg (48.5-82 lb). The upperparts are black and cleanly defined from the white belly, pale yellowish breast and bright yellow ear patches.

Fish form the bulk of the diet but crustaceans, such as krill and squid, are also hunted. The Emperor Penguin is the only penguin species that breeds during the Antarctic winter, trekking 50-120 km over the ice to breeding colonies in the autumn as the sea ice advances. The female lays a single egg, which is incubated by the male alone over the following two months, in colonies of sometimes thousands of individuals. The life span is typically 20 years in the wild, although some observations suggest a feasible lifespan of up to 50 years.

Taxonomy

The Emperor Penguin was described in 1844 by English zoologist George Robert Gray, its generic name being derived from the Ancient Greek a/α 'without' pteno-/πτηνο- 'feather' or 'wing' and dytes/δυτης 'diver'.[2] Its specific epithet is in honour of the German naturalist Johann Reinhold Forster, who accompanied Captain James Cook on his second Pacific Voyage and officially named five other penguin species.

Together with the similarly coloured but smaller King Penguin (A. patagonicus), it is one of two extant species in the genus Aptenodytes. Ridgen's Penguin (A. ridgeni) is an extinct species known from fossil bones of the Late Pliocene, around 3 million years ago, in New Zealand.[3]

Description

Adults with chicks, showing relative sizes

The adult Emperor Penguin stands up to 122 cm (48 in) tall and can weigh anywhere from 22 to 37 kg (48.5-82 lb), depending on where it is in the reproductive cycle. Both male and female penguins lose substantial portions of their mass while raising hatchlings and incubating eggs.[4] The adult has deep black feathers dorsally, including the head, chin, throat, back, dorsal part of the flippers, and tail. The black plumage is sharply delineated from the light-coloured plumage elsewhere. The underparts of the wings and belly are white, becoming pale yellow in the upper breast, while the ear patches are bright yellow. The upper mandible of the 8 cm (3.1 in) long bill is black, and the lower mandible can be pink, orange or lilac.[5] Males and females are similar in size and colouration.[4] A juvenile is slightly smaller in size and colouration to an adult; its auricular patches, chin and throat are white and its bill is black.[5] The Emperor Penguin chick is covered with silver-grey down and has a black head and white mask.[5] It weighs around 315 g (11 oz) on hatching, and fledges at around 50% of adult weight.[6]

The Emperor Penguin's dark plumage fade to a brownish colour during November to February, before the yearly moult;[5] this is a rapid process in penguins compared with other birds, taking around 34 days in this species in January and February. Emperor Penguin feathers emerge from the skin after developing to one third total length, and before old feathers are lost, to reduce heat loss. New feathers then push old ones out, before finishing their growth.[7]

The average yearly survival rate of the Emperor Penguin has been measured at 95.1%, with an average life expectancy of 19.9 years. The same researchers estimate 1% of Emperor Penguins born could feasibly reach an age of 50 years.[8]

Vocalization

As the species has no fixed nest sites, an individual Emperor Penguin is unable to use the location of nest-sites to find its partner or chick and hence relies on identifying them by call alone.[9] It utilizes a complex set of calls that are critical to individual recognition between parents, offspring, and mates,[4] displaying the widest variation in individual calls of all penguins.[9] Vocalizing Emperor Penguins use two frequency bands simultaneously.[10] The chick uses a frequency-modulated whistle to beg for food and to contact parents.[4]

Adaptation to cold

The Emperor Penguin breeds in the coldest environment of any bird species; air temperatures may reach −40 °C (−40 °F), and wind speeds may reach 144 km/h (89 mph). Water temperature is a frigid −1.8 °C (29 °F), thus much lower than the average body temperature of 39 °C (100 °F). The species has adapted in several ways to counteract heat loss.[11] Emperor Penguins have a sub-dermal layer of fat which may be up to 3 cm (1.2 in) thick before breeding, but it is the feathers that are responsible for 80-90% of the insulation.[12] The stiff feathers are short and lanceolate (spear-shaped) and densely packed over the entire skin surface. An extra layer of insulation is formed of separate shafts of downy filaments between the feathers and skin. Muscles allow the feathers to be held erect on land, reducing heat loss by trapping a layer of air next to the skin. Conversely, the plumage is flattened in water, thus waterproofing the skin and downy underlayer.[13] Preening is also vital in keeping the plumage oily and water-repellent, and facilitating insulation.[14]

The Emperor Penguin is able to thermoregulate, or maintain core body temperature without altering its metabolism over a wide range of temperatures. Known as the thermoneutral range, this extends from −10 °C (14 °F) to 20 °C (68 °F). Its metabolism rapidly increases below this, although an individual can maintain its core temperature between 37.6 °C (100 °F) and 38 °C (100 °F) down to −47 °C (−53 °F) .[15]Movement by swimming (if in water), walking (if on land), and shivering are two mechanisms for increasing metabolism; a third process involves an increase in breakdown of fats by enzymes, which is induced by the hormone glucagon.[16] At temperatures above 20 °C (68 °F), an Emperor Penguin may become agitated as its body temperature and metabolic rate rise to increase heat loss. The raising and exposing the undersides of its flippers increases body surface area by 16%, facilitating further heat loss.[17]

Distribution and habitat

The Emperor Penguin has a circumpolar distribution, and is found almost exclusively in the Antarctic ranging from 66º to 77º south latitude. It almost always breeds on stable pack ice near the coast and up to 18 km (11 mi) offshore.[4] Breeding colonies usually occur in sheltered areas where ice cliffs and icebergs protect against the wind.[4] Around 80,000 pairs breed in the Ross Sea sector.[18] Major breeding colonies are located at Cape Washington with 20-25,000 pairs, Coulman Island, Victoria Land with 21,708 pairs, Halley Bay, Coats Land with 14,300-31,400 pairs, and Atka Bay in Queen Maud Land with 16,000 pairs.[19] Two land colonies have been reported: the first on a shingle spit at Dion Island on the Antarctic Peninsula,[20] and another on headland at Taylor Glacier in the Australian Antarctic Territory.[21] Vagrants have been recorded on Heard Island,[22] South Georgia, and New Zealand.[23][19]

Behaviour

Emperor Penguins, Ross Sea, Antarctica

The Emperor Penguin is a social animal, both foraging and nesting in groups. It may be active day or night. A mature adult will travel throughout most of the year between the nesting area and foraging areas in the ocean. From January to March, the species disperses into the oceans, travelling and foraging in groups. It is estimated that there are around 400,000-450,000 Emperor Penguins, distributed into as many as 40 independent Antarctic colonies.[19]

American Gerry Kooyman revolutionized the study of penguin foraging behaviour in 1971 when he published his results from attaching automatic dive recording devices to Emperor Penguins. He found the species had reached depths of 265 m (869 ft). He also noted a maximum dive period of 18 minutes in the same report.[24] Later research revealed a small female dived to a depth of 535 m (1,755 ft) near McMurdo Sound. It is possible that it can dive even deeper as the water pressure at these depths impacted on the recording devices.[25] The male and female Emperor Penguin forage for food up to 500 km (311 mi) from colonies while collecting food to feed chicks, covering anywhere between 82 and 1454 km (51 and 904 miles) per individual trip. A male returning to the sea after incubation will head directly out to areas of permanent open water, known as polynyas, around 100 km (62 mi) from the colony.[26]

Emperor Penguin colony

Its swimming speed is 6 to 9 km/h (4 to 6 mph), but they can achieve up to 19 km/h (12 mph) in short bursts. On land, the Emperor Penguin alternates between walking with a wobbling gait and sliding over the ice on its belly, propelled by its feet and wing-like flippers.

As a defence against the cold, the colony of Emperor Penguins forms a compact huddle (also known as the turtle formation) ranging in size from ten to many hundreds of birds, with each bird leaning forward on a neighbour. Those on the outside tend to shuffle slowly around the edge of the turtle, producing a slow churning action, and giving each bird a turn on the inside and the outside.[27]

Diet

The diet consists mainly fish, crustaceans and cephalopods,[28] though its exact composition varies from population to population, but fish is usually the most important food source, and Antarctic silverfish, Pleuragramma antarcticum, is often the most important species of fish eaten. The Emperor Penguin searches for prey in the open water of the Southern Ocean or in ice-free areas of open water and tidal cracks in pack ice.[4] One of its feeding strategies is to dive to around 50 m (164 ft), where it can easily spot the sub-ice fish, Pagothenia borchgrevinki, swimming against the under surface of the sea-ice, which it then catches. It then dives again and repeats the sequence about half a dozen times before surfacing to breathe. The Emperor Penguin may also blow bubbles into the cracks in the ice to drive out the hiding fish.

Predators

Skua flying over Emperor Penguin chicks, Ross Sea, Antarctica

The Emperor Penguin's predators include birds and aquatic mammals; the Southern Giant Petrel (Macronectes giganteus) is the main bird predator, responsible for up to 34% of chick deaths at some colonies. The South Polar Skua (Stercorarius maccormicki) mainly scavenges, as the chicks are too large to be attacked by the time of its annual arrival in the colony.[29]

The primary aquatic mammal predators are the Leopard Seal (Hydrurga leptonyx), which takes fledglings soon after entering the water as well as some adult birds,[14] and the orca (Orcinus orca), which takes adult birds.[30]

Courtship and reproduction

The life-cycle of the Emperor Penguin

The Emperor Penguin is able to breed at around three years of age, and usually commences breeding around 1-3 years later.[6] 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.[31] The trigger appears to be decreasing daylength; Emperor Penguins in captivity have been induced successfully into breeding by using lighting systems mimicking seasonal Antarctic daylength.[32]

The penguins start courtship in March or April, when the temperature can be as low as –40°C (-40°F). A lone male will give an ecstatic display, where it stands still and places its head on its chest before inhaling and giving a courtship call for 1-2 seconds; it then moves around the colony and repeats the call. A male and female will stand face to face, one extending its head and neck up and the other mirroring it before both hold this posture for several minutes. Once in pairs, couples will waddle around the colony together, with the female usually following the male. Before copulation, one bird will bow deeply to its mate, its bill pointed close to the ground, and its mate will do the same.[33]

Emperor Penguins are serially monogamous. They have only one mate each year, and stay faithful to that mate. However, fidelity between years is only about 15%.[33] The narrow window period available for mating appears to be an influence, as there is a priority to mate and breed which often precludes waiting for the previous year's partner.[34]

The egg of the Emperor Penguin. It is 12x8cm and vaguely pear-shaped.

The female penguin lays one 460-470 gram (1 lb) egg in May or early June;[33] it is pyriform (pear-shaped) and pale greenish-white in colour and measures around 12 x 8 cm.[31] It represents just 2.3% of its mother's body weight, one of the smallest eggs relative to maternal weight of any bird species.[35] 15.7% of the weight of an Emperor Penguin egg is shell; like those of other penguin species, the shell is relatively thick to minimise risk of breakage.[36]

At this point the mother's nutritional reserves are exhausted and she immediately returns to the sea to feed for two months.[31] Very carefully, she transfers the egg to the male, who incubates the egg in his brood pouch for 64 days consecutively until hatching.[33] The Emperor Penguin is the only species where this behaviour is observed, as both parents take shifts incubating in all other species.[37] By this time the male will have fasted for around 115 days since arriving at the colony.[33] The transfer of the egg can be awkward and difficult, and many couples drop the egg in the process. When this happens, the chick inside is immediately lost as the egg cannot withstand the low temperatures on the icy ground. To survive the cold and winds of up to 200 km/h (120 mph), the males huddle together, taking turns in the middle of the huddle. They have also been observed with their backs to the wind to conserve body heat. In the four months of incubation the male may lose as much as 20kg going from around 38kg to just 18kg. [38][39]

Hatching may take up to 2-3 days to complete, and chicks are born semi-altricial and nidicolous. In other words, they have only a thin covering of down and are entirely dependent on their parents for food and warmth.[40] The young chick is brooded in what is called the guard phase, spending its time balanced on its parents' feet and sheltered by its pouch.[40] If the chick hatches before the mother's return, the father feeds it a curd-like substance composed of 59% protein and 28% lipid, which is produced by a gland in his esophagus.[41]

Emperor Penguin feeding a chick

The female penguin returns any time from hatching to ten days afterwards, from mid-July to early August.[31] She finds her mate among the hundreds of fathers via his call and takes over caring for the chick, feeding it by regurgitating the food that she has stored in her stomach. The male then leaves to take his turn at sea, spending around 24 days there before returning.[31] His trip is slightly shorter than before, because the melting of ice in the summer gradually decreases the distance between the breeding site and the open sea. About 45-50 days after hatching, the chicks form a crèche, huddling together for warmth and protection while still fed by their parents.[31] A crèche may comprise up to several thousand birds densely packed together and is essential for surviving the low Antarctic temperatures.[42]

Chicks begin moulting from early November into juvenile plumage, which takes up to two months and is often not completed by the the time they leave the colony. Adults also cease feeding them during this time. All birds make the considerably shorter trek back to the sea in December or January and spend the rest of the summer feeding there.[43][14]

Relationship with humans

Cultural references

The Emperor Penguin has been the subject of several documentaries. In 1993, the species was featured in the BBC series Life in the Freezer, presented by David Attenborough. In 2005, the French documentary La Marche de l'empereur, released as March of the Penguins in the United States, told the story of the penguins' reproductive cycle.[44] The BBC and Attenborough covered the Emperor again in the 2006 series Planet Earth. Apsley Cherry-Garrard, the Antarctic explorer, said: "Take it all in all, I do not believe anybody on Earth has a worse time than an Emperor Penguin."[45] The computer-animated movie Happy Feet (2006) features Emperor Penguins as its primary characters, with one in particular that loves to dance, depicting them as endangered by a shrinking food supply. The computer-animated movie Surf's Up (2007) features a surfing Emperor Penguin named Zeke "Big-Z" Topanga.

Conservation status

The Emperor Penguin is listed as least concern by the IUCN. Along with nine other species of penguin, it is currently being considered for placement under the US Endangered Species Act. The primary reasons for this are declining food availability due to the effects of climate change, and industrial fisheries on the crustacean and fish populations. Other reasons for their placement on this list include disease, introduced predators (this is more so for the other species of penguin than it is the Emperor), habitat destruction, and disturbance at breeding colonies by humans. Of particular concern is the impact of disturbance caused by tourism.[46]

Populations declines of 50% in the Terre Adélie region have been noted due to increased adult mortality especially of males during abnormally warm periods (in the late 1970s) with reduced sea-ice extent. On the other hand egg hatching success reduced when the sea-ice extent increased. The species is therefore considered as very sensitive to climatic changes.[47]

References

  1. ^ Template:IUCN2006 Database entry includes justification for why this species is of least concern
  2. ^ Liddell, Henry George and Robert Scott (1980). A Greek-English Lexicon (Abridged Edition). United Kingdom: Oxford University Press. ISBN 0-19-910207-4.
  3. ^ Williams, p. 13
  4. ^ a b c d e f g University of Michigan Museum of Zoology. "Aptenodytes forsteri". Retrieved 2008-01-01.
  5. ^ a b c d Williams (The Penguins) p. 152
  6. ^ a b Williams (The Penguins) p. 159
  7. ^ Williams (The Penguins) p. 45
  8. ^ Template:Fr icon Mougin J-L, van Beveren M (1979). "Structure et dynamique de la population de manchots empereur Aptenodytes forsteri de la colonie de l'archipel de Pointe Géologie, Terre Adélie". Compte Rendus Academie Science dé Paris. 289D: 157–60.
  9. ^ a b Williams (The Penguins) p. 68
  10. ^ Robisson P. (1992). "Vocalizations in Aptenodytes Penguins: Application of the Two-voice Theory" (PDF) Auk 109(3): 654-658
  11. ^ Williams (The Penguins) p. 107
  12. ^ Williams (The Penguins) p. 108
  13. ^ Williams (The Penguins) pp. 107-08
  14. ^ a b c Kooyman GL, Gentry RL, Bergman WP, Hammel HT (1976). "Heat loss in penguins during immersion and compression". Comparative Biochemistry and Physiology. 54A: 75–80.{{cite journal}}: CS1 maint: multiple names: authors list (link) Cite error: The named reference "Kooy90" was defined multiple times with different content (see the help page).
  15. ^ Williams (The Penguins) p. 109
  16. ^ Williams (The Penguins) p. 110
  17. ^ Williams (The Penguins) p. 111
  18. ^ Harper PC, Knox GA, Wilson GJ, Young EC (1984). "The status and conservation of birds in the Ross Sea sector of Antarctica". In Croxall JP, Evans PGH, Schreiber RW (ed.). Status and Conservation of the World's Seabirds. Cambridge: ICBP. pp. pp. 593-608. {{cite book}}: |pages= has extra text (help)CS1 maint: multiple names: authors list (link)
  19. ^ a b c Marchant, S (1990). Handbook of Australian, New Zealand and Antarctic Birds, Vol. 1A. Melbourne: Oxford University Press. {{cite book}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  20. ^ Stonehouse, B (1953). "The Emperor Penguin Aptenodytes forsteri Gray I. Breeding behaviour and development". Falkland Islands Dependencies Survey Scientific Report. 6: 1–33.
  21. ^ Robertson, G (1992). "Population size and breeding success of Emperor Penguins Aptenodytes forsteri at Auster and Taylor Glacier colonies, Mawson Coast, Antarctica". Emu. 92: 65–71.
  22. ^ Downes MC, Ealey EHM, Gwynn AM, Young PS (1959). "The Birds of Heard Island". Australian National Antarctic Research Report. Series B1: 1–35.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  23. ^ Croxall JP, Prince PA (1983). "Antarctic Penguins and Albatrosses". Oceanus. 26: 18–27.
  24. ^ Kooyman GL, Drabek CM, Elsner R, Campbell WB (1971). "Diving behaviour of the Emperor Penguin Aptenodytes forsteri". Auk. 88: 775–95.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  25. ^ Williams (The Penguins) p. 89
  26. ^ Ancel A, Kooyman GL, Ponganis PJ, Gendner JP, Lignon J, Mestre X (1992). "Foraging behaviour of Emperor Penguins as a resource detector in Winter and Summer". Nature. 360: 336–39.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  27. ^ Pinshow B., Fedak M.A. , Battles D.R, & Schmidt-Nielsen K. (1976) "Energy expenditure for thermoregulation and locomotion in emperor penguins" American Journal of Physiology 231(3): 903-912
  28. ^ Cherel Y. & Kooyman G. L. (1998) "Food of emperor penguins ( Aptenodytes forsteri ) in the western Ross Sea, Antarctica" Marine Biology 130(3): 335-344 doi:10.1007/s002270050253
  29. ^ Williams (The Penguins) p. 40
  30. ^ Prévost, J (1961). Ecologie du manchot empereur. Paris: Hermann.
  31. ^ a b c d e f Williams (The Penguins) p. 158
  32. ^ "The endocrine control of reproduction and molt in male and female Emperor (Aptenodytes forsteri) and Adélie (Pygoscelis adeliae) Penguins. I. Annual changes in plasma levels of gonadal streroids and luteinizing hormone". Gen. Comp. Endocrinol. 62: 43–53. {{cite journal}}: Cite has empty unknown parameters: |month= and |coauthors= (help)
  33. ^ a b c d e Williams (The Penguins) p. 157
  34. ^ Williams (The Penguins) p. 55
  35. ^ Williams (The Penguins) p. 23
  36. ^ Williams (The Penguins) p. 24
  37. ^ Williams (The Penguins) p. 27
  38. ^ Robin, J. P. (1988). "Protein and lipid utilization during long-term fasting in emperor penguins". Am. J. Physiol. Regul. Integr. Comp. Physiol. 254: R61–R68. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  39. ^ Le Maho, Y. (1976). "Thermoregulation in fasting emperor penguins under natural conditions". Am. J. Physiol. 231: 913–922. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  40. ^ a b Williams (The Penguins) p. 28
  41. ^ Template:Fr icon Prévost J, Vilter V (1963). "Histologie de la sécrétion oesophagienne du Manchot empereur". Proceedings of the XIII International Ornithological Conference: 1085–94.
  42. ^ Williams (The Penguins) p. 30
  43. ^ "Moulting starvation in emperor pengion (Aptenodytes forsteri)". Polar Biology. 11: 253–58. 1991.
  44. ^ Template:Fr icon "La Marche de l'empereur, un film de Luc jacquet". Official Site (French). Retrieved 2008-03-19.
  45. ^ Apsley Cherry-Garrard. From the Introduction to The Worst Journey in the World.
  46. ^ Burger J. & Gochfeld M. (2007) "Responses of Emperor Penguins (Aptenodytes forsteri) to encounters with ecotourists while commuting to and from their breeding colony". Polar Biology 30(10): 1303-1313 doi:10.1007/s00300-007-0291-1
  47. ^ Barbraud, C. (2001). "Emperor penguins and climate change". Nature. 411 (6834): 183–186. PMID 11346792. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)

Cited text

  • Williams, Tony D. (1995). The Penguins. Oxford, England: Oxford University Press. ISBN 0-19-854667-X.
Wikimedia Commons has media related to Aptenodytes forsteri.
Retrieved from "https://en.wikipedia.org/w/index.php?title=Emperor_penguin&oldid=199537870"