Death of a colony
Cape Denison holds a special place in the history of Antarctic exploration. A small outcrop of rocks on the remote East Antarctic coastline, Cape Denison is forever associated with one of the most spectacular and often forgotten tales of survival. A century ago it was the main base of operations for one of the great explorers of the south: the Australian scientist Sir Douglas Mawson. Privately funded, three bases and one research ship supported a science team that explored a region the size of the United States between 1911 and 1914. Mawson’s Australasian Antarctic Expedition, however, suffered terribly during their time at Cape Denison: a sudden turn of events led to tragedy on the ice, the death of two men, allegations of cannibalism and with the return of winter sea ice, an extended stay in Antarctica. But when they first came upon Cape Denison, Mawson was ecstatic. Greeted by squawking penguins: ‘We were soon inside a beautiful, miniature harbour completely land-locked. The sun shone gloriously in a blue sky as we stepped ashore on a charming ice-foot…As a station for scientific investigations, it offered a wider field than the causal observer would have imagined.’
|A century ago the Adélie penguin colony at Cape Denison was thriving. Image from the Victoria State Library, Australia.|
The Adélie colony at Cape Denison and neighbouring Mackellar Islets that greeted Mawson and his men are just one of many found along the all too infrequent rocky promontories scattered on the icy coastline of the Antarctic. Numbering several million, Adélie penguins are Antarctic icons with their distinctive jet-black heads and white rings around the eye. Mawson and his men were enchanted by their penguin neighbours and suggested as many as 200,000 individuals lived in the area. In more recent years, however, the environment has been less than kind to the Adélie colony at Cape Denison. In December 2010 conditions changed dramatically when a giant iceberg known as B09B – the size of the Australian Capital Territory – grounded in Commonwealth Bay, leading to a dramatic expansion of sea ice. Returning to Cape Denison as the privately-funded Australasian Antarctic Expedition 2013-2014 we resolved to undertake a multi-disciplinary study on the impact(s) of B09B across the area. A major focus was to add a key data point to a record of population numbers that reaches back a century.
In a recently published study reported in Antarctic Science (freely available to download here) we report the impact of the iceberg B09B on the Adélie penguins between 2011 (the last census date) and 2013/14. We found the number of penguins breeding in the area has declined markedly since the first census, and importantly more recent work. With the associated build up of sea ice in Commonwealth Bay in 2013, the penguins now have to commute about 65 km between colonies where they breed and the open ocean where they feed. Many fewer penguins are now returning to the colonies to attempt to breed and of those that do return most fail to rear their chicks. We observed hundreds of abandoned eggs and thousands of dead chicks. The normally noisy and aggressive Adélie penguins that did reach the colony were so subdued they hardly acknowledged our intrusion into their realm (this is strikingly seen in our movie below); in marked contrast to other colonies in the area that lay considerably closer to the sea ice edge.
Unfortunately, the decline in the colony has been understandably but erroneously reported as the death of 150,000 penguins but this is not the case. We found very few, perhaps no, pre-breeding birds at Cape Denison. With few, if any, young birds prospecting for a place to breed in the future, the local colonies could become extinct within the breeding life of an Adélie penguin (which is typically no more than 16 years). If young birds do not replace the old established breeders as they come to the end of their lives, it seems probable the colony at Cape Denison will become extinct if conditions do not change. Few, if any, adult penguins will have been directly killed by this event; we suspect they have stayed at sea and missed breeding in the mean time. A few may have gone to other colonies but that is unlikely; once a penguin has chosen where it will breed it has a very strong tendency to return to that colony and no other. Intriguingly, ancient penguin bone deposits were found in areas suitable for Adélie penguin breeding but were no longer occupied, suggesting colonization and extirpation events may have occurred in the past, an interpretation supported by studies of ocean sediments offshore over the past four centuries. Importantly, this iceberg stranding event only affects Adélie penguins in the Commonwealth Bay area, the millions of other birds breeding around the rest of Antarctica are not affected.
While it is important to recognise that this study focuses on the Adélie penguin colonies at Cape Denison and the MacKellar Islets, this study provides an important perspective on how devastating the impact of iceberg stranding events can be on fragile Antarctic ecosystems (a message echoed by other work we have published from the area). In particular, with the observed rapid population decline since the arrival of B09B, future monitoring of the Cape Denison Adélie penguins is now urgently required to better characterize their sensitivity to the continuing trend towards more extensive sea ice observed around the East Antarctica coastline.
Kerry-Jayne Wilson(1), Chris Turney(2) and Chris Fogwill(2)
(1) West Coast Penguin Trust, PO Box 70, Charleston 7865, West Coast, New Zealand
(2) Climate Change Research Centre, School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, NSW 2052, Australia