Waterbird breeding colonies in the Top End of the Northern Territory

This is the first report in a series that will document the location and status of selected faunal assemblages on the Northern Territory coastline, offshore islands and Top End floodplains. It addresses colonial waterbird breeding sites and includes species of egrets, herons, cormorants and ibises, and the Australian Pelican, Darter and Royal Spoonbill. Little information existed on the location and status of waterbird breeding colonies in the Top End (north of latitude 16 o 35'S) of the Northern Territory prior to 1990. Information gathered during aerial and ground surveys primarily between 1990 and 1999 have subsequently shown that the coast and major floodplains of the Top End have nationally and globally significant numbers of colonial nesting waterbirds, particularly Intermediate, Great, Little and Cattle Egrets. Seventy-six colonies, confirmed active during the survey period, are here documented. The majority of these colonies were located during surveys by the author, while a few were listed from evidence provided by reliable informants during the survey period. >Colonies were distributed around most of the coast and larger coastal floodplains, extending inland for no further than about 40 kilometres. The most important areas for colonial waterbird breeding were the floodplains between the Moyle and Finniss Rivers and between the Adelaide River and Murgenella Creek. The least important areas were the Tiwi Islands, Cobourg Peninsular, Groote Eylandt and most of the northern part of the Gulf of Carpentaria. Apart from two small colonies on Low Rock and Haul Round Island, no islands supported colonial waterbird breeding (their importance was for seabird breeding and will be discussed in a subsequent report). The vast majority of the colonies were located on either Aboriginal land or pastoral leasehold land. Only 5% of colonies occurred on conservation reserves. This is an issue in need of consideration in the future. Stands of mangrove or paperbark trees were strongly preferred as breeding sites, with some species of waterbird preferring one or the other for nesting sites, while others were found breeding equally in both types. Fifteen species of waterbird breed at these sites, with individual sites having between 1 and 11 species. Colony sizes varied from the low tens to 15000+ adults. As well as having nationally significant numbers of colonies and numbers of birds within them, Top End colonies are important because most are active every year, unlike many colonies in southern Australia. Breeding begins as early as November when Cattle Egrets commence nesting, and continues through to October when the later-breeding Darter, Australian White Ibis and Royal Spoonbill are finishing. The longest duration of any single colony was from November to August. A further 52 colonies, which are not discussed in the main body of the report, have been listed as confirmed breeding colonies in the past, or possible breeding colonies at present. These mostly include colonies that were located from the air but require further investigation for confirmation, and sites appearing in historical records (ie prior to 1990) that may no longer be used, or were unable to be located from the information available. All confirmed colonies are individually detailed in Appendix B and possible colonies in Appendix C. The fauna of the Top End of the Northern Territory is in a very unique position. Not only is there an immense amount of habitat which holds 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 at least the short term, it is equally likely that the pressures of human expansion within Australia will see some of this area targeted for development at some stage in the more distant future. It is for this eventuality that we must be prepared. We must ensure the security of the more significant of these colonies before problems arise.