The Black stilt is a medium-sized wading bird found in New Zealand. It is one of the world's rarest birds that is threatened by introduced feral cats, ferrets, and hedgehogs as well as habitat degradation from hydroelectric dams, agriculture, and invasive weeds. The Black stilt has extremely long pink 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. Black adult plumage appears in their first or second year.
Black stilts are native to New Zealand and breed only in the upper Waitaki River system in the Mackenzie Basin in the South Island. They inhabit braided rivers and nearby wetlands such as swamps, ponds, and lake deltas; some birds can also occur along the coastline.
Black stilts are active during the day but often forage at night. They are generally solitary and spend most of their time wading; they feed by probing, pecking, and also search for prey by moving their bill back and forth. The long bill of these birds allows them to extract prey items even beneath stones. Most Black stilts are sedentary and overwinter in the Mackenzie Basin, but about 10% of the population, especially hybrids and those paired with Pied stilts, migrate to North Island harbors such as Kawhia and Kaipara in January for the winter.
Black stilts are monogamous and pair for life. They usually nest in solitary pairs but may sometimes associate with other pairs of Black stilts and colonies of Pied stilt. Both the male and the female collaborate on building a nest in July or August on stable islands or banks in a shingle riverbed; pairs tend to nest in the same site each year. The nest is a small depression made with twigs, grass, and waterweeds lined with vegetation. It is usually placed in clumps of grass. The female lays 3 to 5 eggs from September to December, peaking in October and both parents incubate them for roughly 25 days. The chicks are able to leave the nest very soon after hatching and it takes them 6-8 weeks to fledge. They remain with their parents for a further 6 to 8 months and start to breed at 2-3 years of age.
Despite 20 years of intensive protection, the Black stilt remains one of the rarest species of wading bird and one of the most endangered birds in the world. Predation from mammalian invasive species poses the greatest threat to the survival of the species. In the 19th century, mustelids such as stoats, ferrets, and weasels, as well as cats, were released into the Mackenzie Country to try to control the spread of rabbits. Black stilts are very vulnerable to these predators: they nest on the banks of streams and rivers, rather than islands; their nesting season begins in late winter, a time when rabbit numbers are low; and they currently nest as solitary pairs, so lose the protection of a colony (although they formed colonies in the past when numbers were higher). Hybridization with far more numerous Pied stilts is also a major threat to the Black stilt gene pool. Throughout their range Black stilts have been almost entirely replaced by Pied stilts, which colonized New Zealand after human settlement. Black stilts are also vulnerable to the loss of their native habitat. They rely on wetlands and braided riverbeds for feeding, and these have been extensively drained or modified for agriculture, irrigation, and flood control. Invasive weeds such as Russell lupin and crack willow are able to colonize braided riverbeds, reducing nesting habitat and providing cover for predators. Because Black stilts nest on braided river beds, they are also threatened by changes in river flows as a result of new and existing hydroelectric dams.
According to the IUCN Red List, the total population size of the Black stilt is 106 adult birds. According to the Wikipedia resource the current wild population is estimated at 169 wild adult birds (as of May 2020). Overall, currently, this species is classified as Critically Endangered (CR) on the IUCN Red List but its numbers today are increasing.