Holl Island and O'Connor Island are situated in the southwest Windmill Islands, Budd Coast, Wilkes Land. Holl Island is roughly triangular in shape and up to 3 km long. O'Connor Island is ~1.7 km long and up to 0.7 km wide and lies ~600 m to the east, separated by a narrow channel and Werlein Island. Both islands are of rocky and hilly topography and are ice free in summer. Holl Island rises to ~90 m, with steep cliffs along the northwestern coast, while O'Connor Island has a maximum elevation of ~80 m. Several small lakes are present on Holl Island.
The IBA qualifies on the basis of the Adélie Penguin (Pygoscelis adeliae) colony present, and comprises Holl Island, O'Connor Island and the intervening islands and marine area.
The nearest permanent station is Casey (AUS), ~14 km to the north on Bailey Peninsula.
Woehler et al. (1991) counted 11 875 breeding pairs of Adélie Penguin on Holl Island and 4748 pairs on O'Connor Island in 1989/90, and noted the colony has been increasing since counts were first made in 1961. This compares with ~30 514 breeding pairs (95% CI 18 443, 49 850) of Adélie Penguin on both Holl Island and O'Connor Island as estimated from January 2011 satellite imagery (Lynch & LaRue 2014). While this more recent count suggests almost a doubling of numbers over 21 years, it is not clear whether this apparent change relates to inter-seasonal fluctuations, methodological differences, or represents a real increase in the local Adélie Penguin population.
Approximately 1084 and 327 breeding pairs of Snow Petrel (Pagodroma nivea) were estimated on Holl Island and O'Connor Island respectively in 2002/03 (Olivier, Lee & Woehler 2004). Although numbers are unknown, Cape Petrels (Daption capense) (Murray & Luders 1990) and South Polar Skuas (Catharacta maccormicki) also breed on both islands, with breeding Wilson's Storm-petrels (Oceanites oceanicus) confirmed only on Holl Island (Woehler et al. 1991; Australian Antarctic Data Centre 2012). Creuwels et al. (2007) estimated 400 breeding pairs of Southern Fulmar (Fulmarus glacialoides) present on Holl Island in 1977/78.
Non-bird biodiversity: Weddell (Leptonychotes weddellii), Leopard (Hydrurga leptonyx) and Southern Elephant (Mirounga leonina) seals have been reported in the area (Murray & Luders 1990; Woehler et al. 1991).
BirdLife International (2019) Important Bird Areas factsheet: Holl Island / O’Connor Island. Downloaded from http://www.birdlife.org on 16/06/2019.