The distribution and status of waterbirds around the coast and coastal wetlands of the Northern Territory

Prior to 1990 there had been little survey work done to assess the distribution and status (primarily their abundance, density and seasonality) of any of the Northern Territory coastal fauna. With the possible exception of some Magpie Goose aerial surveys and some work done in Kakadu National Park, there had also been very little done on assessing this for Top End wetland fauna. Locating and documenting this information for our Top End fauna, prior to instigating necessary management actions, is a vital step in ensuring the future conservation of these animals and their habitats. Commencing in 1990 with the Parks and Wildlife Service of the Northern Territory, I began a series of extensive aerial and ground surveys to locate and document the distribution and status of selected faunal assemblages (mostly aquatic birds, marine turtles and cetaceans) along the Northern Territory coastline, on offshore islands and in Top End coastal wetlands. This is the fourth in a series of reports being written from information collected during these surveys. Individual reports are based on the different species groups surveyed. (For the purposes of these reports the aquatic birds were considered separately as shorebirds, seabirds and waterbirds, even though shorebirds are also waterbirds). The three previous reports in the series considered waterbird and seabird breeding colonies, and shorebirds. This current report summarises the distribution and status of 66 selected migratory and resident waterbird species (i.e. not including shorebirds). It covers all species of waterbirds not previously included in the earlier report dealing only with colonial breeding waterbirds. This current report also details the non-breeding distribution and status of the (13) colonial breeding species which were only discussed in terms of their breeding colony status in the earlier report. As with each of the previous reports, this current report has been produced as an overview of waterbird distribution and status, with the main aim of assisting future management and research priorities. More detailed papers on species and areas will be written at a later date following further analysis of the data. Over the 16 year period I made nearly 70 000 separate records, totalling a cumulative 5.6 million individuals in the survey area. Of these, nearly 30 000 records, totalling a cumulative 2.6 million individuals, were of the waterbird species detailed in this report. (For the purpose of these reports a record is a single count that differs by species, location and/or time). These records and other information gathered during my aerial and ground surveys have clearly shown that the Top End floodplains and coastal wetlands of the Northern Territory support internationally important numbers of many species of waterbirds in highly favourable habitats. Waterbirds were recorded on all parts of the Northern Territory coast, on many of the islands and throughout the vast areas of tidal and freshwater wetland. Within the survey area of the Top End, 31 separate wetland areas were documented as regionally significant for these taxa. Many of these are of national significance and at least 22 are of international importance (they would for example qualify for Ramsar listing) based solely on numbers of waterbirds. This is very much a minimum number of areas, as many of these areas could be further divided and still qualify; such are the numbers of birds present. Further, the addition of shorebird numbers to many other wetland areas would see them also elevate to Ramsar status on numbers of waterbirds and shorebirds combined. There are also many additional wetland areas that would qualify for Ramsar (or East Asian-Australasian Shorebird Network) status with shorebird numbers alone. These have been discussed in the previous report in this series (Chatto, 2003). Waterbirds were recorded in greatest numbers in several areas. Of particular importance were the wetlands around the Keep River/Legune Station area in the far south west, and the wetlands between the Moyle and Finniss Rivers, and between the Adelaide River and Murgenella Creek in the north west of the Top End. Further important areas across the northern part of the Top End included the wetlands of the Liverpool/Tomkinson Rivers and the Glyde/Goyder Rivers (Arafura Swamps) and the southern part of Arnhem Bay. Along the east coast of the Top End most waterbirds were recorded in wetlands associated with the northern parts of Blue Mud Bay, the Roper River area and the Port McArthur area in the south east. Most of the species discussed in this report were found throughout the survey area, and many were found in greater numbers than previously suspected. Of the resident species, Magpie Goose, all four species of egrets and Australian White Ibis were recorded as the most abundant waterbirds. Other extremely abundant resident waterbird species included Pied Heron, Nankeen Night Heron and Masked Lapwing. Of the species that have most of their population leave the area to breed (either regularly or irregularly), many were recorded in large abundances when they were present in the survey area. These included both whistling-duck species, Grey Teal, Glossy and Straw-necked Ibis, Brolga, Black-winged Stilt and Whiskered Tern, and the migratory Gull-billed, Common and White-winged Black Tern. Species that do not normally appear in large groups, but for which the survey area was nationally important because of their high total numbers, included Green Pygmy-goose, Great-billed Heron, Black-necked Stork, Osprey, Brahminy Kite, White-bellied Sea Eagle Chestnut Rail and Comb-crested Jacana. Many of the waterbirds discussed in this report breed in the survey area. Around 13 species breed in large mixed species breeding colonies. The breeding of these colony species is covered to a certain extent in this report, but have been discussed in much greater detail in a previous report in this series (Chatto 2000b). Magpie Goose breeding was recorded and is discussed but has been reported on in more detail by other authors. The breeding of most of the remaining resident waterbirds was not well studied in these surveys. With the exception of the large and obvious stick nests belonging to Blacknecked Stork and the large coastal raptors, little emphasis was given to searching for single breeding pairs in these surveys. Waterbirds, like most of the other fauna of the Top End of the Northern Territory, are in a unique position. Not only is there an immense amount of habitat which supports large populations of many species, but most of the area is very remote and has not been subject to many of the pressures associated with large human populations. Although this is likely to remain the case for the short term at least, it is equally likely that the pressures of human expansion within Australia, especially in coastal areas, will see some of this area targeted for development, such as broad-acre irrigation schemes, at some stage in the not too distant future. It is for this eventuality that we must be prepared. We must ensure the security of the more significant of these areas before problems arise. Locating key coastal fauna sites and documenting them in this series of reports is the first step in that process.