Oystercatchers (Family Haematopodidae)
South Island oystercatcher, Lake Linden, 1993. Photographer R. Smith. Crown Copyright, Department of Conservation
David Thompson and Peter Moore
General Description
Oystercatchers belong to the family Haematopodidae and these distinctive birds are found throughout the world. The group is relatively uniform in structure and plumage and hence the relationships between species are unresolved. There is a single genus, Haematopus, and 11 species.
Oystercatchers are black or pied birds with long, straight, reddish-orange bills, and they have loud, shrill calls and elaborate "piping" displays which they use to defend their territories. They are typically coastal, living especially in rocky areas, but also on sandy beaches and mudflats, and inland areas, such as braided rivers and farmland. Most species are sedentary, but some migrate and flock when not breeding. They feed on molluscs and crustaceans, including hard-shelled prey such as barnacles, chitons, and limpets, which they chisel or hammer off rocks with their sturdy and tapered bills. Soft prey include polychaete and oligochaete worms and insects.
Oystercatchers are solitary breeders and have long-lasting pair bonds. Nests are spaced out in defended territories and are crude scrapes, which may be lined with nearby material. Oystercatcher clutches have two to four eggs, incubation lasts 25-28 days, and chicks become mobile as soon as their down dries, allowing them to fledge in five to six weeks.
Status
Three species of oystercatcher breed in New Zealand, and all are endemic. The Chatham Island oystercatcher (CIO), H. chathamensis, is classified as "endangered" according to the IUCN classification. This is because of a very small population (less than 250 birds) on the Chatham Islands group. However, a recent increase in the population has accelerated in the late 1990s-early 2000s with intensive predator control at two managed sites in northern Chatham Island. Birds start to breed at two years, which is early for oystercatcher species. Two other species on mainland New Zealand are not currently considered of conservation concern. They were in serious decline in the mid-1800s-early 1900s, apparently a result of hunting, but since their protection in the 1940s, have increased dramatically. The variable oystercatcher (VO), H. unicolor, population approximately doubled in the 1970s-1990s to 4000 birds. There are three colour types, black, pied or intermediate, hence their name. The South Island oystercatcher (SIO), H. finschi, has increased from 49,000 to 85,000 birds in the 1970s-1990s.
Key Locations
The CIO breeds only on the Chatham Islands group, where it is found on Chatham Island, and Pitt, South East, and Mangere islands, in rocky and sandy habitats. The VO is found on coasts of the main islands, and is most abundant at the north and south ends of each island, but also on Stewart Island, and nearby islands. The SIO breeds mainly in inland areas east of the Southern Alps and has large over-wintering populations of up to 10,000 birds at Kaipara and Manukau harbours, the Firth of Thames, and between Nelson and Farewell Spit.
Typical Habitats
The coastal species breed in a variety of habitats ranging from open sand or pasture, sparse vegetation or turfs, rocks, headlands, caves, or overhangs. Generally the sites give incubating birds good views for territorial defence or escape from disturbance predators. Nests are usually in or close to the feeding areas. These also vary widely, from rocky tidal platforms to beaches, stream mouths, estuaries and mudflats, and farmland. SIO nest on stony islands and edges of braided riverbeds, farmland, fringes of lakes and subalpine bogs, but after breeding they migrate to estuaries and sandy beaches.
Summary of Threats
All species suffer losses from introduced predators. The key introduced predator of CIO is the feral cat, which is abundant and preys on eggs, chicks and adults. Mustellids are absent on the Chathams but are important predators of the mainland species. Trampling by farm stock is an issue in unfenced coastal areas, however, pastures have probably favoured the expansion of SIO through increased feeding and breeding opportunities. Although the wholesale shooting of birds on estuaries ceased in the early 1900s, and this has encouraged a population increase, there are now other pressures (eg, recreational vehicles and dogs). Habitat modification has reduced nesting opportunities. Eggs on the coast are vulnerable to high seas, and this has been exacerbated by the elimination of sparse native dune vegetation on gently sloping dunes which favoured oystercatcher nesting in the past. Introduced marram forms dense thickets on steeply sloped dunes, which force birds, especially CIO, to nest closer to the high tide mark. Ironically, the conservation efforts to revegetate South East Island may have reduced the nesting potential for CIO, causing a local decrease in the population there. Spread of lupin and other weeds on braided rivers eliminates breeding areas of SIO.
All species are vulnerable to any effects on the quality of coastal, estuarine and river feeding habitat, for example, through farm and city runoff or oil spills. Global warming may also have adverse impacts on the biota of these areas.
State of Information
Distribution and population information is good for all species. Ecology and breeding information is good, less so for VO. No genetic work has been done to establish relationships between the New Zealand species and other members of the group.
Significance for Maori
Known to Maori as torea, these birds were praised for their ability to dig up and prise open large quantities of bivalve molluscs, and were often personified as people who were digging or weeding the gardens.
Key References
Baker, A J. 1975. Morphological variation, hybridization and systematics of New Zealand oystercatchers (Charadriiformes: Haematopodidae). Journal of Zoology (London) 175: 357-390.
Birdlife International 2003. Birdlife's online world bird database: the site version 2.0 Cambridge, UK: Birdlife International. www.birdlife.org
Heather, B and Robertson, H. 1996. The field guide to the birds of New Zealand. Penguin, Auckland.
Marchant, S and Higgins, P J. 1993. Handbook of Australian, New Zealand and Antarctic birds, Vol 2. Raptors to Lapwings. Melbourne, Oxford University Press.
Moore, P, O'Connor, S, Hedley, G and R Goomes. 2001. Chatham Island oystercatcher - report of 1999/2000 field season. Science & Research Internal Report 189.
Orbel, M. 2003. Birds of Aotearoa. A Natural and Cultural History. Reed Publishing. 198pp.
Taylor, G A. 2000. Action plan for seabird conservation in New Zealand. Part A. Threatened Seabirds. Threatened Species Occasional Publication No. 16. Department of Conservation, Wellington, New Zealand. 233pp.
Taylor, G A. 2000. Action plan for seabird conservation in New Zealand. Part B. Non-threatened Species. Threatened Species Occasional Publication No. 17. Department of Conservation, Wellington New Zealand. 435pp
Table 7: Oystercatchers (Family Haematopodidae) in New Zealand
| Taxon | Common name | Breeding Species | Endemic Species |
|---|---|---|---|
| Haematopus chathamensis | Chatham Island oystercatcher | 1 | 1 |
| Haematopus finschi | South Island oystercatcher | 1 | 1 |
| Haematopus unicolor | Variable oystercatcher | 1 | 1 |
| Total | 3 | 3 |