No abstract

The presence or absence of 61 waterbird species on 95 wetlands in south-western Australia was related to six wetland characteristics: salinity, emergent vegetation, water depth, pH, phosphorus level and wetland size. More species were associated with salinity and vegetation than with other wetland characteristics. There were more positive associations with brackish than with fresh or saline wetlands and few species occurred in hypersaline wetlands. Trees or shrubs and sedges were the vegetation with which most species were associated; few species were recorded on completely open wetlands or those with only samphire. The 95 wetlands were classified into five groups on the basis of waterbird use. All wetland characteristics differed between groups but larger differences occurred in salinity, vegetation and water depth. The wetland group that supported most species also supported the highest numbers of waterbirds and most breeding species.

In total, 58 species of waterbird were recorded on the grassed floodplain of the Middle Fly during surveys in December 1994 and April 1995. The floodplain is an important dry-season habitat both in New Guinea and internationally, with an estimated (+/- s.e.) 587249 +/- 62741 waterbirds in December. Numbers decreased 10-fold between December and April to 54914 +/- 9790: the area was less important during the wet season when it was more deeply inundated. Only magpie geese, comb-crested jacanas and spotted whistling-ducks were recorded breeding on the floodplain. The waterbird community was numerically dominated by fish-eating species, especially in December. Substantial proportions of the populations of many species that occurred on the Middle Fly in December were probably dry-season migrants from Australia, suggesting that migration across Torres Strait is important to the maintenance of waterbird numbers in both New Guinea and Australia.