Kakï, the black stilt, is one of the world’s rarest and most endangered birds. Once widespread and common in many parts of New Zealand, Kakï are now essentially restricted to the Mackenzie Basin, South Canterbury. Kakï are New Zealand’s only endemic member of the avocet and stilt family, their closest relatives being Poaka, the pied stilt, Himantopus himantopus, which are widespread throughout the world’s warm and temperate regions.
Adult Kakï look quite distinctive with their completely black plumage, long red legs and fine black bill. Young Kakï are sometimes confused with Poaka, as they do not attain fully black plumage until 15–18 months of age. Juvenile and sub–adult Kakï tend to have variable and sometimes mottled black markings, whereas adult Poaka have distinct black markings on their back, hind–neck and collar.
Kakï live in braided rivers and associated wetland habitat in the Mackenzie Basin. They usually occur near the stable banks of small streams and sidebanks of major rivers but also use swamps, tarns, ponds and seepages. Kakï can move large distances between rivers and wetlands, but unlike other river birds most Kakï are non–migratory and remain in the Basin throughout the year.
Kakï feed mainly on aquatic invertebrates, small fish and molluscs, and will move around to exploit temporary food sources (eg feeding habitat exposed by receding lake levels). They walk through shallow water and peck at visible prey such as mayfly larvae and water boatmen. If mayflies and caddisflies are hidden beneath submerged stones, Kakï will probe wrybill fashion under stones. In very muddy pools, midge larvae and worms are captured using a technique known as scything, where the bill is swept back and forth through the mud like avocet species.
Unlike Poaka, Kakï pairs are often solitary breeders. Nesting sites are generally near water, for instance on the banks of small streams and side braids of major rivers, on islands and by swamps. The breeding season extends from August to February, with peak egg laying in October. Both sexes build the nest, which consists of varying amounts of grass, twigs and waterweeds thrown together on a bank. Both parents share in the incubation, swapping at roughly hourly intervals. The chicks hatch with their eyes open and leave the nest almost immediately. They soon become nimble and expert hunters while being guarded by at least one parent. Young chicks will freeze when a parent gives an alarm call, while older chicks run and hide.
Kakï will sometimes pair up with Poaka if a Kakï mate is not available. At present there are many more males than females in the wild and it appears the extra males breed with Poaka rather than not breeding at all. While the hybrid offspring produced by these pairs are fertile, their offspring are only half as likely to survive as the offspring of pure Kakï pairs. As a result, hybrids are likely to become less common as more female Kakï are added to the wild population.
At present there are no more than 61 adult Kakï in the wild, and of these only 14 are known to be female. Just seven productive breeding pairs exist in the wild. In the 1800s Kakï were widespread and common throughout much of New Zealand, however a widespread and sustained decline saw Kakï breeding become confined to the Mackenzie Basin by around 1960. The main causes of the decline are thought to have been the introduction of mammalian predators and habitat loss following European colonisation. Within the Mackenzie Basin, the loss of most birds from the 1940’s to 1960’s may have resulted from prey–switching by feral cats and ferrets associated with large–scale rabbit control.
Kakï have been intensively managed since 1981, first by the Wildlife Service and more recently by DOC’s Twizel Area Office. Numerous management techniques have been trialed, with variable success. The new, recently approved Kakï Recovery Plan (2001) sets out two overlapping phases of recovery for the next ten years. The first phase aims to increase kakï numbers in the wild in the short–term, while the second phase aims to identify and overcome the causes of breeding failure and adult mortality in the wild.
Captive rearing and release of Kakï chicks (phase one) is at present a key element of the recovery programme. The goal is to boost the wild Kakï population and thereby reduce the likelihood of extinction in the short–term. Kakï eggs are collected from both wild and captive pairs, and are artificially incubated until hatching. The captive–reared young are later released into the wild, either as juveniles in summer, or as sub–adults in September. Over recent years, the survival of released birds has increased considerably, most likely because iodine is now included in the diet of captive birds and supplementary food is supplied in the first weeks after release. Changes to the diet of captive birds has also resulted in increased egg fertility and increased chick survival, meaning greater numbers of birds are being released.
Research–by–management (phase two) will be crucial to developing ways of protecting the Kakï population in the long term. For instance, we need to find out why Kakï adults and chicks die in the wild, and how we can effectively control the suite of predators that are a threat to wild Kakï. Ferrets, feral cats and other predators are known to kill most eggs and chicks in the wild. Weeds in riverbeds exacerbate the problem by providing cover for predators and making it more difficult for Kakï to detect their presence. A range of research projects are currently underway to address these issues. With directed management and research the outlook for Kakï is very good, and the long–term goal of re–establishing this special bird in rivers and wetlands throughout its former range is becoming increasingly likely.
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40 cm., 220g., adults entirely black, pinkish red legs, black bill, red eye; juveniles are black and white.
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d’Urville, Dumont, Voyage au Pole Sud et dans Oceanie sur Les Corvettes L’Astrolabe et La Zelee – Atlas d’Histoire Naturelle, published 1841–54.
Gould, John, Birds of Australia, 1840–48.
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Saturday, 24 May 2014; ver2009v1