The black stilt is one of the world's rarest wading birds. By 1981 its numbers had dropped to only 23 birds in the wild. By August 2000 the numbers had recovered to only 48 birds in the wild, with another 20 birds in captivity.
It is found in the braided rivers and swamps of the Upper Waitaki Basin, in the middle of the South Island.
The black stilt is larger than the more common pied stilt, with shorter legs. It is also fiercer and hardier, able to wade out into the deeper parts of the river and to survive the harsh winters of the Mackenzie Basin.
Black stilts feed on water insects (mayflies, damselflies), molluscs (water snails) and small fish.
Each pair of black stilts looks after their own nest and territory, hoping that the camouflage marking of the eggs and chicks will help protect them from predators. It is more vulnerable to predators than the pied stilt. Both will pretend to have a broken wing to try and lure the predator (cat, rat, ferret, weasel or stoat) away from its nest, but this is more successful for the pied stilt. The black stilt does not have the safety of numbers and is often attacked by harriers and black-backed gulls.
Unlike pied stilts, black stilts build their nests on dry riverbanks. This makes their nests vulnerable because predators can reach the nests overland or through shallow water. Electric fencing and trapping have been used to try and control predators but they remain a constant danger.
The habitat of the black stilt has been threatened by hydroelectric power development, with canals replacing rivers, and flooding or diversion of rivers. Black stilts have been forced to nest away from their usual braided riverbeds to areas where predators could attack them, and which do not have the same rich food supply.
Other threats to their habitat have included the spread into the remaining braided rivers of introduced plants such as broom, gorse, willow and lupin. Human activities such as recreational fishing and boating, the use of four-wheel drive vehicles along the riverbeds, and the presence of dogs also threaten the black stilt's survival.
From 1992-1999 only eight (4%) of 189 chicks that hatched in the wild reached two years of age. Management of the birds in the wild has included attempts to make their nesting areas predator-free. With other endangered species in New Zealand it has been possible to establish secure populations on off-shore islands. However there are no islands with the braided river habitat which the black stilt needs to survive.
Because the black stilt can produce a large number of eggs each breeding season, the black stilt recovery programme hopes to increase the bird population by removing eggs from nests and hand-rearing the chicks for release into the wild breeding population. This is currently done in Twizel and is going well.