London, Aug 1 The world's largest colony of King penguins in the southern Indian Ocean has shrunk by nearly 90 per cent in the last three decades, yielding the territory to encroaching vegetation, an alarming research has found.
The colony of King penguins -- Aptenodytes patagonicus Miller -- at Ile aux Cochons, Iles Crozet, in the southern Indian Ocean was known in the 1980s as the largest King penguin colony and the second largest penguin colony in the world.
At the time, the colony included 500,000 breeding pairs and consisted of over two million penguins.
Due to isolation and inaccessibility, aerial photographs, and satellite images were used to report on changes in the colony and population sizes over the past 50 years.
The photographs confirmed that the colony's penguin population has plummeted, said Henri Weimerskirch from the Centre d Etudes Biologiques Chize (CNRS) at the Universite de la Rochelle in France.
The population of penguins has declined by 88 per cent over the past 35 years, from 500,000 pairs to 60,000 pairs.
The data, appearing in the journal Antarctic Science, showed that the decline began in the late 1990s, coinciding with a major climatic event in the Southern Ocean related to El Nino.
The size of the colony may also subject it to density-dependent effects. That is, the larger the population, the fiercer the competition between individuals, slowing the growth of all members of the group, the researchers said.
The repercussions of lack of food are thus amplified and can trigger an unprecedented rapid and drastic drop in numbers, especially following a climatic event like the one at the end of the 1990s.
Diseases such as the Avian cholera which is currently ravaging populations of seabirds on other islands in the Indian Ocean, could also be one of the explanations.
Still, none of these possibilities seems to offer a satisfactory explanation for a decline of the magnitude observed on Ile aux Cochons.