Scientists at British Antarctic Survey (BAS) have recently described the loss of a small colony of emperor penguins on an island off the West Antarctic Peninsula.

Emperor penguins [File photo]

The loss is attributed to reduced sea ice, which provides an important nesting substrate for the penguins as well as an important foraging habitat.

Reporting in the February edition of the scientific journal PLoS ONE researchers from BAS and Scott Polar Research Institute say that this is the first time the disappearance of an emperor penguin colony has been documented.

The Emperor Penguin is the tallest and heaviest of all living penguin species and is endemic to Antarctica.

The male and female are similar in plumage and size, reaching 48 inches in height and weighing anywhere from 49 to 99 pounds. The dorsal side and head are black and sharply delineated from the white belly, pale-yellow breast and bright-yellow ear patches. Like all penguins it is flightless, with a streamlined body, and wings stiffened and flattened into flippers for a marine habitat.

The small colony of birds on Emperor Island was found in 1948 when scientists observed 150 pairs gathering there to breed.

However, since 1970 the numbers have been declining steadily and in 2009 a high resolution survey from the air revealed no remaining trace of the colony. The decline and loss of the colony relates closely to a rise in local air temperature and seasonal changes in sea ice duration, associated with climate change.

Lead author Dr Phil Trathan from BAS says, "It is not clear whether the colony died out or relocated. Emperor penguins are thought to return each year to the sites where they hatched, but the colonies must sometimes relocate because of changes in the sea ice. It is clear that emperor penguins are vulnerable to changes in sea ice and the one site in Antarctica where we have seen really big changes in ice is the West Antarctic Peninsula. For much of the 20th century, this region has warmed at an unprecedented rate, particularly in recent decades. Continued climate change is likely to impact on future breeding success."

The paper also explores alternative hypotheses of perhaps why the colony may have disappeared, including possible effects from competition with fisheries, impacts from tourism, disease and unusual weather conditions. The authors suggest that at least the first two of these suggestions can be discounted, and that there are no data to support the remaining two.

The emperor penguin is currently under consideration 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 potential placement on this list include disease, habitat destruction, and disturbance at breeding colonies by humans. Of particular concern is the impact of tourism. One study has shown Emperor Penguin chicks in a créche to become more apprehensive following helicopter approach.

Population declines of 50% in the Terre Adélie region have been observed due to increased adult mortality, especially of 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. The species is therefore considered to be highly sensitive to climatic changes.