Site description (2015 baseline)
Avian Island is a small island lying ~0.5 km south of Adelaide Island in Marguerite Bay, on the western side of the Antarctic Peninsula. Avian Island is one of the most ornithologically important sites in the Antarctic Peninsula region, and is designated as ASPA No. 117. The IBA qualifies on the basis of the Adélie Penguin (Pygoscelis adeliae), Imperial Shag (Phalacrocorax [atriceps] bransfieldensis), and South Polar Skua (Catharacta maccormicki) colonies present, and is defined by the boundary of the ASPA. The ASPA includes the littoral zone, offshore islets and rocks and a 100 m buffer zone around the shoreline.
Avian Island is of rocky, low relief rising to 40 m, with an irregular coastline. The southern coastline features steep cliffs with rocky ledges, suitable for small nesting birds. Other bird habitats include scattered rocks and boulders, ice-free ground, and a gently sloping, well-drained northern shoreline. Several ephemeral freshwater ponds, meltwater channels and small streams are present. Strong tidal currents are common in the surrounding sea, helping to keep coastal waters ice-free. In addition, strong winds reduce snow accumulation, resulting in more favourable conditions for bird colonisation (ASPA No. 117 Management Plan, 2013). Vegetation is sparse across Avian Island and dominated by lichens and mosses.
The nearest permanent scientific station is Teniente Luis Carvajal (CHL), a summer-only station lying ~1 km from Avian Island on the southern shore of Adelaide Island. No long-term meteorological records are available for Avian Island. However, at Carvajal Station the mean daily maximum temperature was 3°C in February for the period 1962-74, whilst the mean daily minimum was –8°C in August for the same period (ASPA No. 117 Management Plan, 2013). Most snowfall occurs between August and October, with light precipitation occurring through the austral summer.
Seven bird species are known to breed on the island, more than at most other sites in the region. An Adélie Penguin colony occupies much of the northern half of the island with 35 600 breeding pairs estimated in 1979, representing one of the largest breeding colonies on the Antarctic Peninsula. Two recent censuses in 2013 estimated 77 515 pairs (Sailley et al. 2013) and 47 146 pairs (Casanovas et al. in press), although the reasons for the discrepancy between the counts is unclear. A large Imperial Shag colony has been recorded on the southwestern coast of the island, totalling 670 pairs in 1989 (unpublished data S. Poncet pers. comm. 2005), and 302 breeding pairs were observed in 2013 (W. Fraser pers. comm. 2013, cited in ASPA No. 117 Management Plan, 2013). Avian Island holds the largest breeding colony of Southern Giant Petrel south of the South Shetland Islands, with 250 breeding pairs recorded in 1990 (Poncet & Poncet 1990), 237 chicks estimated in 2001 (Harris 2001), and 470 breeding pairs recorded in 2013 (W. Fraser pers. comm. 2013, as previous). A colony of around 60 pairs of Kelp Gull (Larus dominicanus) breed near the southern extent of their range on Avian island (Poncet & Poncet 1979). Approximately 195 pairs of South Polar Skua were breeding in the central and eastern parts of the island in 2004 (W. Fraser pers. comm. 2015), with 880 non-breeding individuals also counted on the island (W. Fraser pers. comm. 2015, in correction of data reported in Ritz et al. 2006). The southernmost record of breeding Brown Skua (Catharacta antarctica) has also been documented on Avian Island and several hundred pairs of Wilson's Storm-petrel (Oceanites oceanicus) breed in rocky outcrops around the island (Poncet & Poncet 1979).
Non-breeding species observed on Avian Island include the Antarctic Tern (Sterna vittata), Southern Fulmar (Fulmarus glacialoides), Antarctic Petrel (Thalassoica antarctica), Cape Petrel (Daption capense), King (Aptenodytes patagonicus) and Chinstrap (Pygoscelis antarctica) penguins.
Non-bird biodiversity: Weddell Seals (Leptonychotes weddellii) and Southern Elephant Seals (Mirounga leonina) commonly haul out and breed on Avian Island (ASPA No. 117 Management Plan, 2013). Non-breeding Antarctic Fur Seals (Arctocephalus gazella) also frequent the island with several hundred present on low-lying ground and beaches in February 2001 (Harris 2001). Leopard Seals (Hydrurga leptonyx) are also occasionally observed on Avian Island.
BirdLife International (2023) Important Bird Area factsheet: Avian Island. Downloaded from http://datazone.birdlife.org/site/factsheet/avian-island-iba-antarctica on 04/12/2023.