OYSTERCATCHERS: HaematopodidaeVARIABLE OYSTERCATCHER (Haematopus unicolor): SPECIES ACCOUNT
Oystercatchers vary in length from 15.8 to 19.8 inches (40 to 49 centimeters) and in weight from 0.9 to 1.5 pounds (400 to 700 grams). Some oystercatcher species have dark feathers throughout the body while others are dark with white feathers on the lower breast, belly, and parts of the wings and tail. All-dark oystercatcher species tend to be somewhat larger than black-and-white oystercatchers. One species, the variable oystercatcher, has individuals with both coloration patterns as well as individuals that are somewhere between the two. Oystercatchers have bright red or orange bills with a blade-like or dagger-like shape. The eye and a narrow ring around the eye are red in Old World oystercatcher species. In New World species, the eyes are yellow while the eye rings are either yellow or orange-red. The legs are pink and the feet are stout, with toes that are partially webbed. Oystercatchers have short necks, long, pointed wings, and short tails. Females are larger than males in oystercatchers, and also have longer wings and bills.
Oystercatchers are found in coastal habitats worldwide, including North America, Europe, Africa, east Asia, Australia, and New Zealand. They also inhabit lakeshore areas in New Zealand, temperate (mild) Europe and Asia, and northern Africa.
Oystercatchers occupy diverse types of shoreline habitat. These include beaches of rock, sand, pebble, and shell. Some species can be found in marshes or coastal lagoons. A small number of species live on agricultural land or pastures.
Oystercatchers eat many different types of marine invertebrates, including mollusks, crabs, chitons (KYE-tunz; a type of mollusk), sea urchins, and snails. They also occasionally eat fish. Inland oystercatcher populations focus on arthropods such as insects and spiders. Oystercatchers use their sensitive bills to search for food in shallow water or soft mud. They are effective hunters that are able to defeat their prey using a variety of techniques. With mollusks, oystercatchers sometimes stab their narrow bills into a slightly open shell. They may also pound mollusks against sharp rocks to crack them open.
BEHAVIOR AND REPRODUCTION
Most species of oystercatchers are migratory, moving from breeding areas during the breeding season to nonbreeding grounds in the winter. Many individuals return to the same locations from one year to the next. All species defend territories from other members of the species during the breeding season, and some defend territories year-round. In oystercatchers that are not territorial during the winter, such as the African black oystercatcher, individuals gather in large numbers for better protection against predators, animals that hunt them for food. This behavior also helps individuals stay warm in cold climates. Oystercatchers sometimes also gather in flocks to forage, or search for food. Foraging flocks in coastal species tend to have no more than fifty individuals, but in inland oystercatchers, groups of as many as a thousand individuals are sometimes observed. The oystercatcher call is commonly described as a trill followed by a loud peep.
HELPING CHICKS SURVIVE
Oystercatchers have a difficult time successfully raising young. Many eggs are washed away by storms before they even hatch, and chicks, when they do hatch, are often taken by predators. Because of the danger of predators, oystercatcher chicks become fully mobile within a day of hatching, and are able to run and hide from danger. Parents also feed chicks for a long period of time, helping them grow quickly in order to better escape predators.
Oystercatchers breed during the summer in most parts of the world. All species are monogamous (muh-NAH-guh-mus), that is, a single male breeds with a single female during the breeding season. In many cases, individuals also keep the same mate from year to year. Courtship in oystercatchers is sometimes called "piping" because it involves a male and female singing a single "piped" note together while walking, running, or flying next to each other, making frequent synchronized turns. Nearby pairs often perform the piping routine at the same time. The piping routine is also used to alert other members of the species to the boundaries of a pair's territory.
Females lay between one and four eggs at a time, usually two or three. Nests are simple hollows on the ground, either unlined or lined. Both parents help incubate, or sit on, the eggs. Eggs hatch after between twenty-four and thirty-nine days. Chicks are colored gray-brown to blend into their environments. They are able to leave the nest within a day of hatching. However, parents continue to feed the chicks for at least sixty days after hatching. Most oystercatcher pairs are only able to raise one offspring successfully during each breeding season. Storms can wash away eggs, and chicks are frequently lost to predators.
OYSTERCATCHERS AND PEOPLE
It is sometimes claimed that oystercatchers help deplete oyster beds used by humans, but there is no evidence to back up these claims.
Of the seven species of oystercatchers in existence, one is considered Endangered, facing a very high risk of extinction, and one is considered Near Threatened, in danger of becoming threatened. Chatham Island oystercatchers are Endangered. There are only 100 to 150 individuals left in their natural habitat on four small islands in New Zealand. Chatham Island oystercatcher populations did increase in number during the 1990s as a result of predator removal from critical habitat areas and artificial incubation of eggs. African black oystercatchers are considered Near Threatened. Populations number about 4,800 total. African black oystercatchers have been affected primarily by human disturbance, particularly off-road vehicles and other coastal human recreation.
Physical characteristics: The variable oystercatcher is about 18.5 to 19.3 inches (47 to 49 centimeters) in length. Males weigh about 1.5 pounds (678 grams) while females are a little heavier at 1.6 pounds (724 grams). The variable oystercatcher is the only species that includes all black individuals as well as black-and-white colored individuals. Some individuals have a coloration that is intermediate between the two primary types. They are known as "smudgies." The eye, eye ring, and bill are all red in this species.
Geographic range: The variable oystercatcher is found exclusively on the coasts and islands of New Zealand.
Habitat: Variable oystercatchers occupy rocky and sandy seashore areas.
Diet: Variable oystercatchers eat primarily marine invertebrates such as bivalves, crabs, snails, and polychaetes (PAHL-ee-keets; marine worms).
Behavior and reproduction: Variable oystercatchers are territorial, but occasionally form flocks. There is frequent breeding between differently colored variable oystercatchers. The breeding season occurs in December and January. Nests are built on beaches and sand dunes. Females typically lay three eggs which hatch after twenty-five to thirty-two days.
Variable oystercatchers and people: No significant interactions between variable oystercatchers and people are known.
Conservation status: Variable oystercatchers are not officially considered threatened at this time. However, the total population is only about 3,900 individuals. Variable oystercatchers have been affected by human disturbance and predation by introduced mammals. ∎
FOR MORE INFORMATION
BirdLife International. Threatened Birds of the World. Barcelona: Lynx Edicions, 2000.
del Hoyo, J., A. Elliott, and J. Sargatal, eds. Handbook of the Birds of the World. Vol. 3, Hoatzin to Auks. Barcelona: Lynx Edicions, 1996.
Perrins, Christopher, ed. Firefly Encyclopedia of Birds. Buffalo, NY: Firefly Books, 2003.
"Family Haematopodidae (Oystercatchers)." Animal Diversity Web. http://animaldiversity.ummz.umich.edu/site/accounts/classification/Haematopodidae.html#Haematopodidae (accessed on April 22, 2004).
"Haematopodidae (Oystercatchers)." The Internet Bird Collection. http://www.hbw.com/ibc/phtml/familia.phtml?idFamilia=55 (accessed on April 22, 2004).
"Oystercatchers." Bird Families of the World, Cornell University. http://www.es.cornell.edu/winkler/botw/haematopodidae.html (accessed on April 22, 2004).