Post-fledging and winter migration of Adelie penguins Pygoscelis adeliae in the Mawson region of East Antarctica

Seven fledging Adelie penguin Pygoscelis adeliae chicks and 4 post-moult adults were satellite tracked using the Argos system during the winters of 1995-97 and 1998, respectively. Six fledglings departed from Bechervaise Island near Mawson station (67degrees 35' S, 62degrees 49' E) during late February of 1996 and 1997 and were tracked for up to 5 mo before transmissions stopped. The 7th fledgling left Magnetic Island near Davis station (68degrees 33' S, 77degrees 54' E) in February 1995 and was tracked for 32 d. All fledglings travelled northward initially, then westward along the edge of the fast ice or in the pack-ice, Fledglings had travelled between 536 and 1931 km to the west of their natal colonies by the time transmissions ceased. Adult Adelie penguins were tracked between March and October 1998, following completion of their annual moult at Bechervaise Island. Instruments were set to transmit for 2 h every 10th day over the first 5 mo and 1 d in 4 thereafter. Adult birds travelled westward until July, after which time they moved north within the expanding pack-ice into known areas of high krill concentration before returning eastward toward their breeding sites. Penguin movements over the winter months were closely related to those of sea ice in the region. Ice motion patterns were in turn influenced by gyral oceanic current systems and wind. We propose that large gyral oceanic systems provide a means, for Adelie penguins to reduce costs of transport as they travel into regions of high productivity during winter and return to their breeding colonies in spring.