Variable oystercatcher facts for kids
Quick facts for kids Variable oystercatcher |
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| Mottled variant | |
| Conservation status | |
| Scientific classification | |
| Genus: |
Haematopus
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| Species: |
unicolor
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The variable oystercatcher (Haematopus unicolor) is a special type of bird found only in New Zealand. It's a wader, which means it's a bird that often walks in shallow water to find food. This bird belongs to the oystercatcher family. In the Māori language, it's called torea-pango. People also sometimes call them 'red bills' because of their bright beaks.
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About the Variable Oystercatcher
The name "variable" describes how these birds look. Their feathers on the front can be black and white (pied), a mix of black and white (mottled), or completely black. This means they are polymorphic, having different natural forms. The amount of white on their bodies can depend on where they live; birds from the north usually have more white than those from the south. For example, all variable oystercatchers on Stewart Island are black.
These birds have pink legs, orange rings around their eyes, and bright orange-red beaks. Their beaks are long and thin, like a needle, and turn a deeper red during the breeding season. Male oystercatchers weigh about 678 grams, and females are a bit heavier at around 724 grams. They are usually 42 to 47 centimeters long from their beak to their tail. They have a strong, short body and a thick neck.
You can tell variable oystercatchers apart from the South Island pied oystercatcher (SIPO) because variables are slightly larger. SIPO birds weigh around 550 grams. If a variable oystercatcher is completely black, it's easy to identify. But if it's black and white, it can look similar to a SIPO. However, variable oystercatchers have less clear lines between their black and white feathers. They also have a mottled (mixed color) band on the front edges of their underwings. Their white patch on their lower back is smaller, just a band across the base of the tail, unlike the SIPO's wider, wedge-shaped patch. When they have a mottled look, they are sometimes called "smudgies." Even though males and females look alike, females are usually a little bigger.
Where Variable Oystercatchers Live
Haematopus unicolor is found only in New Zealand. This is because these birds tend to stay in one place and do not migrate (travel long distances). This keeps all their groups within the same island home.
You can often see them in pairs along the coast all around New Zealand. They live along most of the North, South, and Stewart Island coastlines, and on some smaller islands nearby. They are less common on the western coastlines but are found in larger numbers in areas like Northland, Coromandel Peninsula, Bay of Plenty, Greater Wellington, Nelson/Marlborough, and Fiordland.
Preferred Homes and Habitats
Variable oystercatchers like many different types of coastal areas. They usually stay within 30 kilometers of the coast. They prefer sandy beaches for breeding and nesting, often far from muddy harbors.
Sometimes, after heavy rain, you might see them in grassy fields, but they mostly stay around coastal beaches, estuaries (where rivers meet the sea), and shorelines. They like sandy areas and tend to avoid beaches with lots of gravel or large rocks. For their nests, they make a small dip in the sand or shingle, sometimes lining it with seaweed. They usually build these nests on the shore, between rocks, or in sand dunes.
Life Cycle and Reproduction
Variable oystercatchers do not travel to special places to mate. Instead, they breed on the coastal sand dunes where they live most of the year.
When a male oystercatcher finds a possible mate, he will perform a special display. This show helps to impress the female and scare away other males. During this display, the bird will dip and tilt its head while making loud "piping" calls. They also use these movements to mark their territory outside of the mating season, as adult birds prefer to live alone.
Once a female chooses a male, they stay together for the rest of the mating season. They might even stay together for several years in a row. While breeding, the pair will protect their territory, sometimes very aggressively.
Stone-colored eggs, usually 2 or 3 at a time, are laid from September to December. Both parents take turns sitting on the nest to keep the eggs warm until the chicks hatch. Nests are simple scrapes in the sand, often hidden by some plants. Both parents also take turns guarding the nest from animals that might try to eat the eggs or chicks.
The chicks hatch and learn to fly between February and March. This period, called fledging, lasts about 20 to 50 days, but can be longer. During this time, the adult birds might also start to lose their old feathers and grow new ones. This usually happens between December and July.
At about 6 weeks old, the chicks can fly. They start looking for their own food within their parents' territory. By early August, the young birds leave their parents and join other young oystercatchers in a loose group. These young birds stay together until they are about 2 years old. Then, they go off to find their own territories and mates.
After breeding, variable oystercatchers might be seen in or near groups of black and white South Island pied oystercatcher (SIPO), which also have bright orange beaks. Variable oystercatchers are thought to become adults at around 3 years old. Most start breeding when they are between 3 and 6 years old. We don't know the average age of the species, but some banded birds have lived as long as 32 years in New Zealand.
When they fly, they make a high-pitched "kleep kleep" sound. They usually lay 2 to 3 eggs, but sometimes up to 5. The eggs are typically stone-colored with small brown spots. Eggs hatch in 25 to 32 days. The chicks are very well camouflaged (hidden by their color) and can fly in about 6 weeks. These birds can live for about 27 years.
Diet and Foraging
Variable oystercatchers look for food both during the day and at night. They usually don't feed for two hours before or after high tide. They start feeding again as the tide goes out. They mostly find food by looking for it. But when it's dark, or if food is hidden in the sand, they will poke their beaks randomly into the ground to find it.
Their diet includes many different types of shellfish (like clams), crabs, worms, small insects, and sometimes small fish. They mainly eat bivalves (shellfish with two shells). They open these shells by stabbing and twisting them with their beaks. Some birds have even been seen hammering the shells open. After heavy rain, they sometimes go inland to search for earthworms.
Challenges and Threats
In the past, up until 1922, variable oystercatchers were hunted by people for food. This caused their numbers to drop a lot. Adult birds can be hunted by animals like possums, cats, and dogs.
Animals that prey on their nests and chicks include kelp gulls, silver gulls, swamp harriers, Australian magpies, skuas, weasels, dogs, cats, and possibly rats.
Human activities can also disturb variable oystercatchers, which can damage their nests. Losing coastal sand dunes, which are important breeding spots, is a big problem for these birds. Fishing nets and oil spills also pose dangers to the species.
Additionally, some variable oystercatchers have parasites, like certain types of tapeworms. One specific tapeworm, Taenia increscens, is found only in variable oystercatchers. Recently, a tapeworm was found in a bird in Tasman Bay, which was the first time a wild bird was known to have that specific tapeworm. These parasites usually don't harm the birds much; they just take a small amount of the bird's food. Diseases are also not a major cause of death for these birds. Avian pox has been seen in them, but it doesn't seem to be a big problem and rarely causes death.
Conservation Status
Across New Zealand, there are currently estimated to be about 4,000 to 5,000 variable oystercatchers in total. Even though this number seems low, the species is considered to be of "least concern" for its survival. This means experts believe it is in good health overall.
While there are no specific conservation programs just for variable oystercatchers, other laws that protect threatened coastal birds also help these oystercatchers. The number of variable oystercatchers has grown over the past few generations, and it is expected to keep increasing.
In New Zealand, H. unicolor has a national conservation status of "At Risk, Recovering." However, in the Wellington region, it is considered "Regionally Vulnerable," meaning it faces more challenges in that specific area.
Images for kids
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Mottled variant
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Black variant
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Black variant oystercatcher chicks
See also
In Spanish: Ostrero variable para niños
