Variable Oystercatcher

The Variable Oystercatcher, known scientifically as Haematopus unicolor, is a striking wader endemic to the shores of New Zealand. Its name reflects the variability of its plumage, which can range from all black to pied, with mottled individuals known colloquially as "smudgies." These birds exhibit polymorphism, with northern populations typically displaying more white than their southern counterparts. All individuals from Stewart Island, however, are black. They possess pink legs, an orange eye ring, and a bill that is orange-red, needle-like in shape, and darkens during the breeding season. Males average around 678 grams, while females are slightly larger at approximately 724 grams. Their robust build is complemented by a short, sturdy body and a thick neck, with a length ranging from 42 to 47 cm from beak to tail.

Identification Tips

The Variable Oystercatcher is distinguishable from the South Island Pied Oystercatcher (SIPO) by its larger size and the less defined boundary between its black and white plumage. The underwing of the Variable Oystercatcher features a mottled band, and its white rump patch is merely a band across the base of the tail, unlike the SIPO's wide wedge shape. When pied, the Variable Oystercatcher's plumage may appear less sharply contrasted than that of the SIPO.

Habitat

This species is strictly coastal, never venturing more than 30 km from the shoreline. It favors sandy beaches over gravel or boulder-strewn areas and is often found nesting between rocks or on sand dunes. After rainfall, these birds may venture into pastures but remain predominantly coastal dwellers.

Distribution

The Variable Oystercatcher is found along most coastlines of New Zealand's North, South, and Stewart Islands, as well as some offshore islands. They are less common on the western coasts but can be found in higher densities in specific regions such as Northland and the Coromandel Peninsula.

Behaviour

These birds are typically seen in pairs and lead a sedentary lifestyle with little to no migration. They are known to be territorial, especially during the breeding season, and may exhibit aggressive behavior to defend their territory.

Song & Calls

In flight, the Variable Oystercatcher emits a high-pitched 'kleep kleep' sound, which can be heard over the sound of the waves.

Feeding

The Variable Oystercatcher feeds both day and night, avoiding the high tide period. It primarily consumes molluscs, crustaceans, worms, and small invertebrates, using its bill to stab and twist open bivalves or hammer them open. After heavy rains, they may seek earthworms inland.

Breeding

Breeding takes place on coastal sand dunes, with the male performing a territorial display involving 'bowing' movements and piping calls. The species is monogamous during the breeding season, with pairs defending their territory. They lay stone-colored eggs with brown patches, usually in clutches of 2-3, which both parents incubate. Chicks are camouflaged and fledge in about 6 weeks.

Conservation Status

The Variable Oystercatcher is classified as Least Concern, with an estimated population of 4,000–5,000 individuals. It is considered to be in acceptable health and is showing a population increase. The species is listed as "At Risk, Recovering" nationally, with a "Regionally Vulnerable" status in the Wellington region.

Predators, Parasites, and Diseases

Historically hunted for food, the Variable Oystercatcher now faces predation from mammals such as possums, cats, and dogs, as well as threats from human activities and habitat loss. It is also susceptible to parasites like cestodes and trematodes, but these do not significantly harm the birds. Disease is not a major concern for the species, with avian pox documented but not causing significant mortality.