Oystercatchers are stocky birds with bright eye-rings and long colourful bills. Their diet is much more varied than their name implies. There are three species in New Zealand, all of which are endemic.
South Island pied oystercatcher
The South Island pied oystercatcher (Haematopus finschi), sometimes simply called SIPO, is the most common oystercatcher in New Zealand, numbering around 112,000 birds in 1994. Its Māori name is tōrea. It has a black head and upper surfaces, and a white belly. A white notch in front of the folded wing distinguishes it from the pied morph (colouring) of the variable oystercatcher. The pied oystercatcher has a red bill, orange eye-ring and short pink legs. It measures 46 centimetres and weighs 550 grams.
In late winter, South Island pied oystercatchers migrate from beaches and estuaries to inland rivers or farmland, mainly in the South Island, where they breed from August. Nests are a shallow scrape on open riverbeds or farmland. They lay one to three brown, blotched eggs, the parents sharing incubation. Chicks can fly at six weeks.
From December, after raising their young for the year, they return to feeding grounds in the North or South Island, where large flocks gather on sand spits and estuaries, or near a river mouth. Their chief ports of call include Farewell Spit, the Firth of Thames, and Kaipara and Manukau harbours.
On the coast, they probe into mud or wet sand, or picking from the surface, they feed on molluscs, estuarine worms and small fish. Inland, they feed on worms and grubs.
South Island pied oystercatchers start breeding from the age of four or five, and they live up to 27 years.
The variable oystercatcher (Haematopus unicolor, tōrea or tōreapango) is found on rocky and sandy beaches. It is rarer than the South Island pied oystercatcher, with a population of about 5,000 birds.
Also known as the black oystercatcher, it varies from black-and-white to pure black, with the black morph more common further south. It has a red bill and red-orange eye-ring, and pink legs. Larger than the South Island pied oystercatcher, it measures 48 centimetres and weighs 725 grams.
Birds of a different feather
The variable oystercatcher has different colour morphs: some birds are all black, some have a smudged black-and-white belly, and some a pure white belly. This third type can be hard to distinguish from the pied oystercatcher, also black-and-white. The thing to look for on the variable oystercatcher is the more blurred boundary between black and white across the chest. There is also no white line between the chest and the folded wing, and the white bar on the upper wing is indistinct.
These birds remain around the coast to breed. The diet, therefore, is largely marine, including mussels, oysters, limpets and crabs. After heavy rain they will invade coastal fields for a meal of worms and insect larvae.
Nests are a shallow scrape above spring-tide level, and two or three eggs are laid from September to December. Both parents incubate, and chicks are able to fly at six weeks.
Once in serious decline due to hunting, the variable oystercatcher has been protected since 1906. They live for up to 27 years.
Chatham Island oystercatcher
With a population of about 300 birds in 2006, the endemic Chatham Island oystercatcher (Haematopus chathamensis) is endangered. However, in the 1980s and 1990s there were only 100.
This species is confined to the Chatham, Pitt, Rangatira and Māngere islands. They measure 48 centimetres and weigh 600 grams. Cats, the flightless weka, and skuas are the main predators, with the added danger of occasional high seas swamping the nests.
Since a conservation programme in the late 1990s to trap the predators and restore habitat, the bird has made a swift comeback. However, given their restricted habitat, it is unlikely the species will ever be numerous.
These birds live on the coast all year, feeding on molluscs, crabs, invertebrates, and marine worms. Starting in October–December or later, they nest in a shallow scrape often under coastal vegetation for protection from skuas. They lay one to three olive-brown spotted eggs. Both adults incubate, females mainly during daylight. Chicks can fly at seven weeks old. They usually live about eight years, but can live to 19.
Giving nature a nudge
To help Chatham Island oystercatchers successfully breed, conservation staff sometimes place old tyres filled with sand on the beach. This makes an ideal platform to lay eggs, safe from high seas. As soon as the bird lays its eggs, staff move the tyre even further away from the threatening waves.