The black stilt or kakī (Māori), Himantopus novaezelandiae, is found only in New Zealand, and is the world’s rarest wading bird: less than 100 adults survive in the wild. Adult kakī have distinctive black plumage, very long red legs, and a long thin black bill. Black stilts currently breed only in the Mackenzie Basin in the South Island, and are threatened by introduced feral cats and ferrets, as well as habitat degradation from hydroelectric dams, agriculture, and invasive weeds.
Black stilts are one of several species in the genus Himantopus, classified along with avocets in the family Recurvirostridae. Although genetically and behaviourally distinct from pied stilts (Himantopus himantopus), they are able to successfully hybridise with them; hybridisation and dilution of the gene pool is one reason black stilts are threatened with extinction. Black and pied stilts in New Zealand represent two invasions of pied stilt ancestors from Australia: the first, long ago, giving rise to melanistic descendants, the second in the early 19th century.
Black stilts are a medium-sized (220 g) wader with extremely long pinkish-red legs, red eyes, distinctively black plumage, and a long slender black bill. Juveniles have a white breast, neck and head, with a black patch around the eyes, and black belly feathers that distinguish them from pied stilts. Black adult plumage appears in their first or second year. Black plumage may be an adaptation to “absorb heat better in the cold, windswept habitat of glacial riverbeds and lakeshores“.
Although black stilts currently breed only in braided river systems in the South Island, subfossil bones show that prior to human arrival they were found in habitats as diverse as narrow bush streams in Hawkes Bay, and a wetland lake surrounded by forest in North Canterbury. In the nineteenth century they bred on riverbeds and in wetlands of the central and eastern North Island and most of the South Island except Fiordland. As late as the 1940s they were still common in South Canterbury and Central Otago, and nesting occurred in Central Otago as late as 1964. Throughout their range they have been almost entirely replaced by pied stilts, which colonised New Zealand after human settlement and now number approximately 30,000.
Currently black stilts breed only in the upper Waitaki River system in the Mackenzie Basin. Most black stilts will also overwinter in the Mackenzie Basin, but about 10% of the population, especially hybrids and those paired with pied stilts, migrate to North Island harbours such as Kawhia and Kaipara in January for the winter.