Oystercatchers
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.
Pied oystercatcher
The pied oystercatcher or torea is the most common oystercatcher in New Zealand, numbering around 112,000 birds in 1994. The New Zealand subspecies (Haematopus ostralegus finschi) is the South Island pied oystercatcher or SIPO. It has a black head and upper surfaces, and a white belly. A white Y pattern between the chest and the folded wing distinguishes it from the pied phase of the variable oystercatcher. The pied oystercatcher has a red bill, orange eye-ring and short pink legs, measures 46 centimetres and weighs 550 grams.
Breeding
In early spring, 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 winter 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.
Pied oystercatchers start breeding from the age of four or five, and they live up to 27 years.
Variable oystercatcher
The variable oystercatcher (Haematopus unicolor, torea or toreapango) is found on rocky and sandy beaches. It is rare – there were around 3,500 birds in 1994, and they are found only in New Zealand.
Also known as the black oystercatcher, it varies from black and white to pure black, which is more common further south. It has a red bill and red-orange eye-ring, and pink legs. Larger than the pied oystercatcher, it measures 48 centimetres and weighs 725 grams.
Birds of a different feather
The variable oystercatcher has different colour phases: 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.
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 (but up to five) 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 is now protected. They live for up to 27 years.
Chatham Island oystercatcher
With a population of only 220 birds in 2004, the endemic Chatham Island oystercatcher (Haematopus chathamensis) is endangered. However, in the 1980s and 1990s there were only 100. With assistance from conservation managers, it is hoped that numbers will soon reach 500.
This species is confined to the Chatham Islands and South East and Pitt 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 breed, conservation staff 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.
