The emperor penguin ( Aptenodytes forsteri ) is a southern aquatic bird representative of the Sphenicidae family and the Sphenisciphormes order. The Sphenicidae family includes all extant penguin species, which are widely distributed in the southern hemisphere.
The species was described by Gray in 1844 and dedicated to the German naturalist Johann R. Forster, who actively participated in Captain James Cook’s voyages, extensively navigating the world in the discovery of the so-called “ terra Australis incognita” .
The genus refers to the impossibility of the species to fly and that it is capable of submerging itself in water. Emperor penguins have been a source of admiration and fascination since the first expeditions to Antarctica .
They are the birds that are distributed and live further south, in ecosystems practically unaltered by human activities. However, due to the increasing influence of global climate change, the survival of the species may be compromised in the coming decades.
A. forsteri is a bird with congregational habits in the reproductive season. Currently a total of 53 reproductive colonies are known and an estimate of mature adults of approximately 595,000 specimens. Despite these estimates, population trends for the species have not recently been assessed.
These penguins take advantage of the resources available near the fixed ice shelves. The diet contemplates extraordinary variations according to seasonality and the population density of the prey.
Emperor penguins are diving predators. In general, they can have dives whose duration varies significantly depending on the success of capturing the food or if they are just exploratory dives. Foraging time also varies based on seasonality and length of the day.
Its immersion capacity is quite changeable. They generally dive to depths less than 100 meters, however, they have been recorded at depths of 200 meters and a maximum of almost 500 meters.
Emperor penguins are characterized by being the largest and with the greatest body mass among the current penguin species.
Males are usually slightly more robust than females weighing up to 40 kilograms, while females can weigh up to 30 kg. Both sexes can reach heights of up to 1.20 meters.
The coloration is similar in both sexes. The plumage is characteristically black on the back, head, chin, back, dorsal region of the fins and tail. They have a wide white to cream-yellow patch on the neck that fades to white towards the front.
In addition, they have an intense yellow ear region. These yellow spots are almost separated by a deep black band that extends over the shoulders. The belly is white as is the ventral surface of the fins.
The chicks have a coloration similar to the adult. The body is covered by silvery-gray feathers with white patches surrounding the eyes and cheeks, the dorsal region of its head is black and it does not have the yellow lateral spots on the head, but they are white.
These penguins have strong bones to prevent damage during deep dive. In addition to this, they have physiological adaptations similar to that of some mammals that occupy the same habitat.
The hemoglobin of these penguins is very akin to oxygen, so it is very effective at transporting small amounts to the tissues during dives to great depths.
On the other hand, they are able to lower metabolic rates during breeding periods, to withstand the long winter. During which, the males do not feed and incubate their eggs.
Habitat and distribution
Emperor penguins live in the southern hemisphere. They mainly occupy the polar regions of Antarctica, in an elevation range from sea level to 500 meters above the coastal fixed ice caps.
They are concentrated in oceanic marine habitats, intertidal zones and neritic habitats, as well as terrestrial when they congregate for reproductive activities.
These penguins settle on the fixed ice that surrounds the coastal area of Antarctica. Generally their breeding areas are established in areas protected from strong winds either by solid ice walls or icebergs.
There are two representative species of the genus Aptenodytes. Aptenodytes patagonicus is a species very similar to the emperor penguin, however, its size and body mass is considerably smaller. In addition, they differ widely in their behavior, breeding periods and other ecological aspects.
Recently, some phylogenetic works indicate the existence of a common ancestor between penguins and albatrosses that lived in a period between 62 and 73 million years. The genus Aptenodytes diverged about 40 million years ago.
There is evidence of a third species of Aptenodytes in the fossil record, known as A. ridgeni and which lived in the late Pliocene, in New Zealand. So far there are no known subspecies within the emperor penguins.
State of conservation
Until 2012, the species had been listed by the international union for the conservation of threatened species in the category of “Least Concern (LC)”.
However, from that year on, it was considered a “near threatened” species, as a significantly rapid population decline has been evidenced and is expected in the next three generations, given the projections for imminent climate change.
At least three-quarters of spawning populations are estimated to be vulnerable to predicted changes in sea ice conditions, and one-fifth of these may be irreversibly removed by 2100.
The probable decrease in the extension, thickness and concentration of sea ice, as a result of the persistence of the wind and other variables such as temperature and precipitation, are the most worrying factors.
The disappearance of a colony with 150 reproductive pairs on Emperor Island has already been documented. This local disappearance was attributed to the decrease in the seasonal duration of sea ice, particularly stable ice that is suitable for nesting.
Other disturbances currently evident are the establishment of scientific bases for the investigation of the colonies of these penguins and the tourism developed near some of them. Although the percentage of colonies subjected to these pressures is very low.
On the other hand, the development of commercial krill fishing and the collection of silverfish ( Pleuragramma antarcticus ) in Antarctic waters poses a great risk if the nutritional needs of those animals that take advantage of these resources are not considered.
Oil spills also pose a great danger to populations located near the exploitation area.
This species reproduces almost exclusively on fixed ice near the Antarctic coast and even on the coast itself, sometimes penetrating up to 200 kilometers from the open sea.
Emperor penguins have an annual reproduction cycle and are one of the most striking within this group of birds.
Initially, the colonies begin to establish at the end of March and the beginning of April, when the extreme Antarctic winter begins and contrasts with the reproduction period of the other penguin species (spring or summer).
Courtship and selection of partners
Once they are in the nesting sites, a complex mating phase begins. Because there are a greater number of females, they must compete for the company of the males.
Males emit a series of characteristic calls of an individualized nature, the objective of which is to attract the attention of a female in the case of being single or of attracting a partner obtained during the previous reproductive season.
Emperor penguins can establish monogamous reproductive relationships, however, this occurs in 15% of cases due to diverse ecological factors.
Once a bond is established, the male emits a series of movements that are observed and imitated by the female. The male then moves through the colony, usually followed closely by the female. To initiate mating, the male tilts his head towards the ground and is immediately imitated by the female or vice versa.
Laying and breeding
Female emperor penguins only lay one egg that is comparatively smaller relative to other smaller seabirds. The oviposition occurs between May and June.
These birds do not build a nest, a fact that is in contrast to the rest of the penguin species. Once the egg is laid, the female’s energy reserves decrease significantly.
Because of this, the females leave the egg in the care of the males to incubate and undertake a journey back to the coast to feed for about two months.
The transfer of the egg is usually complicated and many of them are lost in the process, because they fall into the ice that is at temperatures down to -40 ° C. The male has a fold or incubation bag lined with feathers from its lower ventral region.
The approximately 500 gr egg rests in perfect balance on the upper region of its legs. The incubation process lasts approximately two months, while the females are absent, which constitutes the longest incubation period among the birds.
Care during growth
The eggs begin to hatch in late July and early August. Up to this point, the male has lost more than 50% of his weight. Initially, the chicks are fed by a substance produced in the esophagus of males with high lipid and protein content.
Once the females return, they replace the males that start to feed and regain weight. About a month later, they return to the colonies and take turns with the females to carry out the rearing and feeding activities in an exchange cycle that can occur more than 5 times.
After the hatchlings reach a size suitable for being left alone, groups or nurseries of them are established. While both parents feed in the ocean.
In early November, the hatchlings begin to shed their juvenile feathers as a starting point and preparation for adopting an independent life at sea during the summer season in late December and January.
During this period, food availability is usually high and a large part of the Antarctic fixed ice is thawed, a fact that increases the probability of survival of the hatchlings that manage to reach this stage.
Emperor penguins descend to a suitable depth by assessing food availability. Once the prey is located, they rise rapidly, attacking schools of fish or isolated fish.
They often catch only one fish per dive with a catch success of 80% for every 90 dives. They can catch more than one fish at a time, when the schools of these are numerous.
This species preys on a wide variety of ocean fish. They have also been reported to eat crustaceans such as krill and mollusks such as squid, which make up an important part of their diet. Squids occupy a significant volume of the diet, as they tend to be highly abundant in some locations.
Between August and October, due to the seasonality of the prey, the Antarctic krill Euphasia superba represents more than 40% of the diet, however, the consumption of krill decreases significantly in December. At this point, the consumption of Psychroteuthis glacialis squid becomes important (up to 63%).
After this period, fish are the main hunting target of penguins. When they are breeding, penguins consume up to 95% of their diet in fish. The most common fish are Pleuragramma antarcticus and Pagothenia borchgrevinki.
During the incubation process, the males make extraordinary efforts to ensure the survival of the chicks. These penguins depend exclusively on the energy reserves obtained before the start of the reproductive period, which indicates that a male can go more than a trimester without eating.
To conserve energy reserves during the cold nights of the Antarctic winter, the males tend to group in circles with their backs to the wind, to conserve heat. This behavior is rotary so that everyone passes through the center of the cluster and the edge exposed to the middle.
When some females fail to mate, they usually adopt young that were left without their parents, that were lost in the colony or due to theft. In most cases they abandon them after two weeks, since they are not able to meet the requirements of the young on their own.
Adopted offspring are usually in varied stages of development, generally during the first two months of life.
BirdLife International 2018. Aptenodytes forsteri . The IUCN Red List of Threatened Species 2018: e.T22697752A132600320. http://dx.doi.org/10.2305/IUCN.UK.2018-2.RLTS.T22697752A132600320.en. Downloaded on 31 October 2019.
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