ABANDONED PENGUIN COLONIES AND ENVIRONMENTAL-CHANGE IN THE PALMER STATION AREA, ANVERS-ISLAND, ANTARCTIC PENINSULA

Six abandoned colonies of Adelie penguin (Pygoscelis adeliae) were exc avated near Palmer Station, Anvers island, Antarctic Peninsula, to inv estigate the occupation history of this species. Sediments from each s ite yielded abundant fish bones and otoliths and squid beaks that repr esent prey remains deposited by penguins during the nesting period. Ra diocarbon analyses indicate that colony occupation began prior to the Little Ice Age (LIA; 1500-1850 AD), with the oldest site dating to 644 yrs before present (sp; average reservoir-corrected date with Is rang e, 603-679 yr sp). Food remains indicate that the non-euphausiid prey of penguins consisted primarily of a mesopelagic squid (Psychroteuthis glacialis) and two species of fish (Pleuragramma antarcticum and Elec trona antarctica). The relative abundance of the first two prey taxa v aried significantly among six sites (chi(2) > 34.6; df = 10; P < 0.001 ) with colonies dating prior to the LIA having greater representation of squid, and less of silverfish, than those occupied during the LIA. Data from control excavations at three modem colonies indicate a diet similar to that of the pre-LIA sites. These results suggest that Adeli e penguins may have changed their diet in response to warming and cool ing cycles in the past. In addition, only Adelie penguins are known to have nested in the Palmer Station area prior to the 1950s; gentoo (Py goscelis papua) and chinstrap (P. antarctica) penguins now breeding in this region have expanded their ranges southward in the Peninsula wit hin the past 50 yrs, in correlation with pronounced regional warming.