Once the common stilt of New Zealand, the endemic black stilt (Himantopus novaezelandiae) remains critically endangered and is considered the world’s rarest wader, despite over 30 years of intensive conservation management.
Black stilts have a distinctive elongated neck, jet-black plumage, red eyes, long red legs and a thin black bill. Due to their variable plumage, juveniles and sub-adults can be easily overlooked amongst pied stilts, while hybrids add to the confusion. Juveniles in their first winter plumage have a black back, smudgy grey hind neck and variable dark markings on the flank. The plumage darkens during their second summer moult, and by mid-summer they are predominantly black. Contact calls are a single or repeated “yep”. Territorial birds are noisy, having a higher pitched and more penetrating call than the pied stilt.
Typical black stilt habitat consists of wideopen braided riverbeds and associated nearby wetlands, ponds and shallow lake edges. During flooding more stable side-streams, swamps and ponds are favoured. Nesting territories are located in areas with abundant food, such as shallow river channels rich in aquatic invertebrates. Outside the breeding season black stilts move locally within the Mackenzie Basin, but small numbers frequent the Canterbury coast (Lakes Wainono and Ellesmere), and Kawhia and Kaipara Harbours in the North Island.
At the time of European settlement this now exceptionally rare wader was widespread throughout New Zealand and bred at North Island locations until the late 19th century. Settlement intensified swiftly, exotic plants and animals were introduced, wetlands were drained and rivers were channelised. The environment changed rapidly and black stilt numbers decreased swiftly to devastatingly low levels. During the 20th century the range contracted from being South Island wide, to being confined to Canterbury and Otago by the 1950s, South Canterbury and North Otago by the 1970s, and the Mackenzie Basin by the 1980s. The breeding population is now restricted to the area between the Lake Tekapo and Lake Pukaki basins in the north, and the Ahuriri River in the south. In 1981 the population fell to just 23 birds, which increased to 55 birds by 2005 and 85 birds in 2010. Before the annual release of captive birds, the free-living population was ~130 birds in 2012. We are now in 2016 and the population continues to increase, but only ever so slowly.
Today black stilts face a wide range of threats including habitat loss and modification (agriculture, hydroelectric development, weed invasions, flooding), introduced mammalian predators (feral cats, rats, hedgehogs and mustelids), avian predation (Australasian harrier and black backed gull), human disturbance (recreational river users disturb nesting adults and crush eggs/chicks), and pied stilt hybridisation (now a lesser issue). The development of irrigation has seen significant changes in land use, particularly modification for conversion to dairy farming, resulting in considerable habitat loss.
To address these threats and increase numbers, the Department of Conservation initiated the Kaki Recovery Programme in 1981. The programme has produced great results by focusing on wild egg collection, artificial incubation, captive rearing of chicks for release, predator control to protect wild populations, research and promoting awareness.
Only two captive facilities globally breed black stilts for release into the wild – the Department of Conservation in Twizel and The Isaac Conservation and Wildlife Trust in Christchurch. To date the Trust has played a pivotal role in black stilt conservation with 45 birds housed per season. Each season three to four clutches are collected from captive breeding pairs. First, second and third clutches are transferred to Twizel for artificial incubation and hatching, while the last clutches remain with pairs at the Trust. Older chicks and juveniles then transfer from Twizel to the Trust for preconditioning until release in the Mackenzie Basin. This process is vital for black stilt survival and resumes each breeding season at both facilities. The Trust aims to expand its operations by constructing separate incubation and brooder facilities by 2020, which will result in fewer transfers and enable more chicks to be held on site.
While intensive conservation management has succeeded at increasing black stilt numbers, the species continues to struggle and remains critically endangered. Annual releases and predator control have prevented black stilt extinction; nevertheless various challenges remain with managing wild populations. Releases on the mainland are limited to certain sites and continue to be a numbers game. In New Zealand many threatened species benefit from predator-free island translocations; however there are no predator-free island habitats with braided river systems. On average 120 chicks (including wild collected eggs), are released annually, slowly increasing the population. However the post-release survival rate is only 33 percent with even fewer birds becoming part of the breeding population. The species long-term survival therefore remains highly dependent on long-term captive breeding efforts and predator control.
How you can help
The Isaac Conservation and Wildlife Trust