Known, new and probable Snow Petrel breeding locations in the Ross Dependency and Marie Byrd Land
Snow Petrels (Pagodroma nivea) breed circurnpolarly in Antarctica. Watson et al. (1971), Harper et al. (1984) and Marchant & Higgins (1990) list breeding sites in the Ross Dependency (160°E-150°W) and also in the unclaimed region of Antarctica (150°W-80°W), which comprises Marie Byrd Land and Ellsworth Highland. Much of the literature on Snow Petrels mentions that their nests are inaccessible on vertical cliffs (Kinsky 1965, Cowan 1981, Harper et al. 1984, Broady et al. 1989) and so are almost impossible to count accurately. The birds usually nest in holes and on ledges on exposed, snow-free cliff faces, although some nests have also been found on gentle slopes below (Strandtman 1978, Broady et al. 1989). Many more expeditions, predominantly geological, have been made to Northern Victoria Land in the Ross Dependency than to Marie Byrd Land, where only five expeditions with accompanying biologists have been made (Siple 1938, Perkins 1945, Rudolph 1967, Strandtman 1978, Broady et al. 1989). Consequently more Snow Petrel breeding sites are recorded for Victoria Land than for Marie Byrd Land. However, the literature reveals that there are sometimes uncertainties in the criteria used to assign breeding site status. The science, necessarily limited to broad-scale observation and collecting because of remoteness, logistics involved, and bad weather in the case of far-ranging deep field parties, suits many geological and botanical expeditions but hampers precise ornithological observations. Many expedition reports mention flocks (small (15 and large > 15 birds) of Snow Petrels near rock outcrops, but this is not strong evidence of breeding. In our updated list of breeding sites we have used the following criteria: (a) birds settling on ledges and disappearing inside cracks on steep cliff faces and birds flying off these ledges, (b) streaks of guano below these ledges, (c) presence of nearby nesting skuas with regurgitated Snow Petrel bones and feathers as evidence of feeding, and (d) the presence of large flocks of birds constantly wheeling around the same rock outcrop. Prolonged observation with binoculars of suspected nests in cliffs is desirable but largely impossible during wide-ranging trips. We have tried to use all the above criteria but for some colonies have had to use a minimum of two because of incomplete data in the literature. We regard several colonies listed by Harper et al. (1984) and Marchant & Higgins (1990) as needing confiiation because they do not satisfy these criteria. Figure 1 gives the locations of the main areas, and Table 1 is a list of Snow Petrel colonies in the region 160°E-80°W, together with locations for nine new colonies. As far as possible nest numbers are given but these, except for those on gentle slopes, should be regarded as estimates.