Late Holocene occupation history of the southernmost Adélie penguin colonies at Cape Royds and Cape Barne, Ross Island, Antarctica

Abstract Cape Royds and Cape Barne on the south-west coast of Ross Island, Antarctica, comprise the most southern active and abandoned Adélie penguin ( Pygoscelis adeliae ) breeding colonies in Antarctica. Surveys and excavations of abandoned penguin breeding sites in this region provide new information on the late Holocene occupation history in relation to past environmental change. While the Cape Royds colony has been occupied by breeding penguins for at least ~800 years, areas to the north and south at Cape Barne have undergone periodic occupation and abandonment for over 4 millennia. A total of 49 radiocarbon dates on penguin tissues from abandoned sites reveal three occupation periods during the late Holocene: a brief period of occupation at ~4100 cal. yrs bp north of Cape Royds, a more extended northern occupation from ~1900 to 3000 cal. yrs bp during a warm interval known as the penguin ‘optimum’ and a shorter occupation of northern sites at ~600–800 cal. yrs bp . A brief but more intense occupation at Cape Barne occurred from ~225 to 483 cal. yrs bp during the Little Ice Age, probably due to increased katabatic winds and less sea ice that kept the McMurdo Sound polynya open and with greater productivity than today. Locations both to the north of Cape Royds and at Cape Barne have had sporadic records of breeding attempts by small numbers of penguins in the 1960s, 1980s and 1990s but for no more than 1 to a few years at a time. These results provide insights into potential reoccupation of these areas by Adélie penguins with current warming trends and the future importance of the McMurdo Sound polynya for penguin conservation.