Bird populations in nine braided rivers of the Upper Waitaki Basin, South Island, New Zealand: changes after 30 years
|Title||Bird populations in nine braided rivers of the Upper Waitaki Basin, South Island, New Zealand: changes after 30 years|
|Publication Type||Journal Article|
|Year of Publication||1999|
|Type of Article||paper|
|Keywords||birds, braided river, comparative survey, density, Upper Waitaki basin|
Sections of nine rivers in the Upper Waitaki Basin were surveyed between 1991 and 1994 and these surveys were compared with counts completed in 1962, 1965 and 1968. A systematic account of 27 wetland birds is given. Densities (number of birds km-1) of birds were compared between the two periods. Species that increased in density were mainly common generalists, whereas species that decreased in density were endemic river breeding specialists. Densities of Wrybills (Anarhynchus frontalis), Spur-wing Plovers (Vanellus miles), Canada Geese (Branta canadensis), and Grey Teal (Anas gracilis) were higher in the 1990s than in the 1960s, whereas densities of Banded Dotterels (Charadrius bicinctus), waterfowl and shags, Black-billed Gulls (Larus bulleri), South Island Pied Oystercatchers (Haematopus ostralegus), Black-backed Gulls (L. dominicanus) and Black-fronted Terns (Sterna albostriata) were lower in at least one river in the 1990s compared to the 1960s. Estimated minimum populations of river birds published for the Ahuriri River (surveyed in 1982) and the Cass River (surveyed in 1979 and 1982) were usually intermediate to those recorded in equivalent 1960s and 1990s surveys. Four mechanisms that explain changes in braided river bird populations are suggested.