Antarctic Science 17 (1): 57–66 (2005) © Antarctic Science Ltd Printed in the UK DOI: 10.1017/S0954102005002427 A 9000-year record of Adélie penguin occupation and diet in the Windmill Islands, East Antarctica STEVEN D. EMSLIE1 and ERIC J. WOEHLER2 1University of North Carolina, Department of Biological Sciences, 601 S. College Road, Wilmington, NC 28403, USA 2Australian Antarctic Division, Channel Highway, Kingston, TAS 7050, Australia [email protected] Abstract: We investigated 17 abandoned Adélie penguin (Pygoscelis adeliae) colonies in the Windmill Islands, East Antarctica, in summer 2002/03. Forty radiocarbon dates on penguin bones and eggshells from 13 of these sites indicate a near continuous occupation by breeding penguins in this region for over 9000 years. These dates refine the recent geological record in this region and indicate that deglaciation of the northern islands occurred much earlier than previously suggested. Dietary remains from these sites include at least 23 taxa of cephalopods and teleost fish. Quantification of these remains indicates significant fluctuations in the relative abundance of two of the more common major prey taxa. The Antarctic silverfish (Pleuragramma antarcticum Boulenger) was the most common teleost prey during all time periods represented by the ages of the sites, but preservational factors may explain a gradual decrease in the remains of this species in increasingly older sites. The most common cephalopod in the sediments was the squid, Psychroteuthis glacialis Thiele, which occurred in low numbers in most sites except one (Site 75). An unusually high number of squid beaks preserved in Site 75, dating to approximately 5700–6100 cal. yr BP, does not correlate with a decrease in fish prey at that time. The high number of abandoned penguin colonies (> 200) in the Windmill Islands may be due to population cycles in the past in association with low nest-site fidelity and movement by breeding penguins to new sites within this region. Received 10 June 2004, accepted 25 October 2004 Key words: abandoned colonies, deglaciation, palaeodiet, Pleuragramma antarcticum, Psychroteuthis glacialis, Pygoscelis adeliae Introduction surface in a gully between abandoned colonies. These dates Adélie penguins (Pygoscelis adeliae Hombron & Jacquinot) indicated that the southern Windmill Islands were have been known to breed in the Windmill Islands, East deglaciated by 8000 corr. yr BP (years before present, Antarctica, since at least the late 1950s, when humans first corrected for the marine-carbon reservoir effect), while the visited this region (Woehler et al. 1991). The breeding northern islands (those north of Robinson Ridge, 66°22'S, population is currently estimated at c. 105 000 pairs at 14 see Fig. 1) did not become ice free until 5500 corr. yr BP. locations (Woehler, unpublished data). Compared to initial However, the exact extent of penguin occupation of the surveys in the 1950s and 1960s, this estimate indicates the region was not investigated. population has increased by over 300% since that time Here, we report on a preliminary study of abandoned (Woehler et al. 1991). However, while the overall colonies in the Windmill Islands to characterize further the population has increased, specific colonies and especially occupation history and diet of Adélie penguins in this those near human habitation have decreased (Woehler et al. region. We concentrated primarily on colonies located in the 1994). northern islands, as defined by Goodwin (1993), with some In addition to the current breeding population of limited work conducted at Robinson Ridge and Peterson penguins, a high number of relict, or abandoned colonies Island in the south. We compare these records to the also have been identified in the Windmill Islands (Goodwin palaeoclimatic history of this region of East Antarctica, as 1993). Investigation of abandoned colonies has been shown evinced by previously published ice core and sedimentary to be an effective means to gather data on the occupation data, to refine the geological history of this region. Finally, history of penguins in a given region, their palaeodiet, and we address the question as to why so many abandoned the climatic conditions that prevailed during the occupation colonies exist in the Windmill Islands using historic and period(s) (Baroni & Orombelli 1994, Emslie 2001, Emslie recent photographic and census data. & McDaniel 2002, Emslie et al. 2003a). Previously, Goodwin (1993) completed a series of radiocarbon dates on Study area and methods peat from lake and pond sediments in the Windmill Islands, and on one Adélie penguin skull found 20 cm below the The Windmill Islands extend for over 130 km along the 57 58 STEVEN D. EMSLIE & ERIC J. WOEHLER Fig. 1. Map showing the location of the Windmill Islands in Antarctica (bottom left) and the locations of major geographic features where abandoned penguin colonies were located (see Table I for GPS locations of the 17 sites discussed in the text). coast of East Antarctica between 66°12'–66°30'S (Fig. 1). addition, modern penguin guano was sampled at two active Numerous ice free shorelines, islands, and marine terraces colonies on Clark Peninsula and Shirley Island. occur within this region with active Adélie penguin colonies Excavations were conducted by establishing 1 x 1 m pits located on Clark and Bailey peninsulas to the north, and near the centre of each abandoned colony. Loose surface extending to Peterson Island to the south (Woehler et al. pebbles not mixed with sediments were removed as level 1 1991). Even though numerous abandoned pebble mounds in each pit to a depth where ornithogenic sediments were occur within one geographic area (e.g. Bailey Peninsula), first encountered, usually 5–15 cm below the present we refer to each of the abandoned mounds as ‘colonies’, and surface. Thereafter, the pit was excavated in 5 cm levels not ‘subcolonies’ as defined by Ainley (2002). We use this until bedrock or the bottom of the ornithogenic sediments more general terminology for our sites since each mound (recognized by a distinct change in colour and texture) was could represent a different occupation period from others in reached. At the conclusion of the excavations, each pit was a given region. Thus, there would be no true subcolonies backfilled with rock and pebbles; surface pebbles with (sensu Ainley 2002) if all the mounds were occupied at vegetation were replaced so that little or no evidence of the different times and designating each one as a colony is pit was visible on the surface. therefore more logical The amount of all excavated sediments was quantified Ground surveys were conducted in January and February using 14 litre buckets to measure the total volume removed 2003 to locate and map abandoned colonies and subcolonies from each level, so that data could be quantified between using Global Positioning System (GPS). While incomplete, levels of different ages in the same and different pits. These these surveys resulted in the identification of hundreds of sediments were then washed through three stacked sieves abandoned colonies, especially near extant colonies. Not all with square mesh sizes of 0.64, 0.32, and 0.025 cm2. of the abandoned colonies that were mapped were Organic remains (bone and feather) from the top sieve were numbered and only 17 were excavated (Table I). These sites sorted and removed during the washing process. Sediments include 11 on Bailey Peninsula, two each at Robinson from the middle screen were dried and sorted in the lab. The Ridge, Clark Peninsula, and at Peterson Island (Fig. 1). In finer sediments from the bottom screen were dried and re- A 9000-YEAR RECORD OF PENGUINS IN THE WINDMILL ISLANDS 59 comparison to other samples. Dietary remains (otoliths and squid beaks) were identified by W. Walker, National Marine Mammal Laboratory, Seattle. These remains are quantified by total number of identifiable specimens and by the minimum number of individuals (MNI) per taxon per excavated level. MNI was Table II. Radiocarbon dates (in yrs BP) on Adélie penguin (Pygoscelis adeliae) bone collagen and eggshell carbonates from abandoned penguin colonies in the Windmill Islands, East Antarctica. Conventional dates were corrected and calibrated for the marine-carbon reservoir effect using a ∆R = 750 ± 50 years (see Emslie 1995) and the MARINE98 database of Stuiver & Reimer (1993). The laboratory number (NZA, Rafter Radiocarbon Lab, New Zealand), conventional date (in 14C yr BP), mean calibrated date (in cal. yr BP), and calibrated 2σ range (95% confidence Fig. 2. Distribution of 40 calibrated radiocarbon dates on penguin interval, in cal. yr BP) also are provided. remains from the Windmill Islands, East Antarctica. Two points are plotted to show the 2σ range in cal. yr BP for each dated Conventional Calibrated sample from 13 sites (see Table II). Site acronyms are: Site/provenience Material Lab. no. date mean range σ BP = Bailey Peninsula, CP = Clark Peninsula, RR = Robinson (2 ) Ridge. Peterson Island Site 1 Level 4 Bone NZA 18038 1356 ± 40 266 396–78 screened through 1 mm and 0.25 mm geology sieves, then Level 5 Bone NZA 18079 1433 ± 40 305 460–238 sorted under a low-power stereomicroscope to recover fish Site 3 Level 8 Bone NZA 18080 2539 ± 40 1316 1476–1229 bones, otoliths, squid beaks and other dietary remains. In Casey station area most cases, the large amount of this fine sediment Site 15 Level 2 Bone NZA 18075 4054 ± 40 3153 3321–2949 necessitated that only a subsample of this sediment could be Level 6 Eggshell NZA 17711 4242 ± 40 3364 3520–3225 sorted in the lab. In those cases, the proportion sorted (a Level 9 Eggshell NZA 17710 9182 ± 55 8925 9284–8802 minimum of 15%) was quantified by dry mass for Site 17 Level 2 Bone NZA 18076 4009 ± 40 3074 3259–2887 Level 3 Bone NZA 18035 4042 ± 40 3137 3313–2939 Level 7 Eggshell NZA 17712 8952 ± 60 8690 8921–8475 Site 30 Level 6 Eggshell NZA 17696 8562 ± 55 8290 8400–8113 Table I.