Impacts of introduced mammalian predators on indigenous birds of freshwater wetlands in New Zealand

The impacts of introduced mammalian predators on the viability of bird populations in forest, river and coastal habitats in New Zealand are well known. However, a common understanding of their impacts in freshwater wetlands is lacking. We review evidence for impacts of introduced mammalian predators on freshwater birds, particularly specialist species restricted to wetlands, and use this information to make predictions about freshwater species likely to be vulnerable to predation. Extinctions and significant declines of freshwater species have been numerous since humans introduced mammalian predators to New Zealand. Anecdotal evidence links predation to the loss of 11 of 14 extinct birds that would have inhabited wetlands. Thirty extant species, particularly ground-nesting species, are still under threat from mammalian predators. All introduced mammalian predator species are abundant and/or widespread in New Zealand wetlands and most have been confirmed to prey upon freshwater bird species. While their precise impacts on the long-term viability of threatened bird populations have not been evaluated, evidence suggests that predation is a serious threat, warranting predator control. An evaluation using documented predation events and ecological traits suggests that six threatened wetland specialists are at high risk of predation: Australasian bittern (Botaurus poiciloptilus), banded rail (Gallirallus philippensis), brown teal (Anas chlorotis), fernbird (Bowdleria punctata), marsh crake (Porzana pusilla), and spotless crake (P. tabuensis). Research is needed on the ecology and behaviour of mammalian predators in wetlands to help understand their impacts on long-term viability of bird populations and to assist in developing and monitoring predator control programmes.