Story: Wading birds
Page 3 – Stilts
The elegant stilts have slender necks and long legs to enable feeding in deep water. In flight their legs trail well beyond their tail.
Since the 1950s, the black stilt or kakī (Himantopus novaezelandiae) has been on the brink of extinction. By 1981 there were only 23 adults in the wild, but conservation efforts have gradually increased the number (90 adults in 2004), lending hope for their survival.
The adult is greenish-black with a long black bill and very long pink legs. It measures 40 centimetres from bill-tip to tail (not including legs), and weighs 220 grams. It is a protected endangered endemic species.
Since its ancestors arrived from Australia tens of thousands of years ago, the kakī has adapted to a colder environment, with only avian predators. In the 19th century the birds were still widespread, but today are found only in the South Island’s Mackenzie Basin. They breed and feed along the shores of streams and lakes.
A shrinking population
There are several reasons for their decline:
- They have few defences against the cats and ferrets that arrived in the 19th century. They do not have the protection of nesting in colonies, nor the distraction displays of their Australian relatives to lure predators away from eggs or chicks.
- Since the 1950s hydro-electric schemes and weed invasion have reduced their Mackenzie Basin habitat.
- The more recently arrived Australian pied stilt, which deals better with predators, hybridises with the kakī, resulting in fewer ‘pure’ black stilts.
The Department of Conservation raises chicks in captivity in three aviaries, and releases them into the wild. Predators are trapped, to safeguard birds in the wild. Project River Recovery was launched in 1991 in partnership with Meridian Energy, restoring some of the Mackenzie Basin habitat by controlling weeds and predators, and digging ponds. This has also benefited other native plants and animals.
Breeding and feeding
They nest in solitary pairs in braided river beds or near wetlands and lay three to five blotched, green eggs from September to December. Both sexes incubate, and the young can fly at six weeks. They live up to 15 years. Foods are aquatic invertebrates, molluscs and fish.
After breeding, kakī do not generally join the northern exodus of inland wading birds. Most remain in the Mackenzie Basin, enduring the sometimes freezing temperatures before breeding begins again in spring.
Slim and graceful, pied stilts or poaka (Himantopus himantopus) can be seen in their thousands at major estuaries and lakes during autumn and winter, before they fly to their breeding grounds in late winter–early spring. They are black on the crown, nape, back and wings, and white elsewhere. They weigh 190 grams and measure 35 centimetres.
A self-introduced species that arrived relatively recently (perhaps around 1800) from Australia, the pied stilt has flourished in its new home – a favourable food supply was released when lowland forests and scrublands were converted to pasture. By 1993 there were around 30,000 birds.
Pied stilts are masterful at distracting enemies from the nest:
[T]hey try to divert attention to themselves by simulating injury, shamming broken legs or wings in a most realistic manner. I have often watched one flying along, when suddenly it would give a loud cry of pain, and flutter to the ground in a lopsided manner as if one wing was broken. There it would flop along for a yard or so, and then lie down, flapping its wings and calling as if in agony. Perhaps it may stagger to its feet again, and then collapse with a drawn out cry of anguish and a last faint flick of the wings, and lie still. 1
Pied stilts breed on South Island riverbeds and around New Zealand’s coast. They breed in colonies of up to 100 nests, which are mounds near water. They lay two to five greenish eggs from August (at coastal sites) or October (inland). Feeding on invertebrates and molluscs, they plunge and snatch underwater, or probe and scythe in wet mud.