Fluctuations in Adélie penguin prey size in the mid to late Holocene, northern Marguerite Bay, Antarctic Peninsula

Abstract

We investigated temporal changes in Adelie penguin prey size in northern Marguerite Bay, Antarctic Peninsula, through excavations of three abandoned and one active colony at Lagoon (67°35′S, 68°16′W) and Ginger Islands (67°45′S, 68°41′W), respectively, in austral summer 1999/2000. Radiocarbon dates on penguin bones and eggshell fragments collected at each site indicate that Lagoon Island was first occupied after 6000 BP and Ginger Island near 2275 BP. Identifiable non-krill prey remains (otoliths and squid beaks) were recovered from ornithogenic soils at all sites, with Antarctic silverfish (Pleuragramma antarcticum) and squid (Psychroteuthis glacialis) being the most abundant species represented in the deposits. Estimated mean standard lengths and mantle lengths of these two prey taxa, based on regressions with otolith and beak measurements respectively, indicate that Adelie penguins primarily select these prey within a mean size range of 95–117 mm. Prey size also varied significantly across seven occupation periods from 6000 BP to the present, but did not correlate with climate change.