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American Oystercatcher

Description

oyster catcherThe American oystercatcher is one of two species of oystercatchers that breed in North America. Oystercatchers are large, conspicuous shorebirds (43-53 cm or 17-21 in) common to seacoasts in temperate to tropical parts of the world. The head and neck are black, and the wings and back are dark brown with distinct white patches that are visible when the bird is in flight. The breast and belly are white, the bill is bright red, and the legs and feet are a pinkish color.

Habitat and Biology

The American oystercatcher breeds along seacoasts from Baja, California, and Massachusetts southward. Wintering grounds are from North Carolina south to the West Indies and Brazil. In South Carolina, oystercatchers inhabit sandy or pebbly beaches, mudflats, and the borders of salt marshes.

Oystercatchers begin to breed in early to late April. During this time, they exhibit aggressive behavior towards neighboring pairs, often engaging in loud vocalization displays. Once the oystercatcher finds a mate, they form a long-term pair bond. Nesting in this species does not occur in large colonies as in other shorebirds. Two to four creamy white eggs with dark brown and lavender markings are laid in shallow depressions on isolated beaches. Eggs are usually laid over a 1 to 2-day period. The males generally incubate during the day, while the females incubate at night. Male investment of incubation tends to increase during the duration of incubation, lasting about 24 to 25 days. Oystercatcher young depend almost entirely on their parents for food, an uncommon characteristic among shorebird families. The females take care of brooding the chicks, giving the male time for territorial defense and provisioning the chicks. Some starvation is observed during this time due to the establishment of sibling hierarchies. During winter, oystercatchers change their solitary habits and gather in large flocks. The species' common name derives from its peculiar dietary habits. When the bird finds a gaping oyster, it inserts its long bill inside it, cutting the adductor muscle; the valves can no longer shut, and the oyster is easily obtained. American oystercatchers also feed on other bivalves, such as clams and mussels, snails, barnacles, fiddler crabs, aquatic insects, and sea worms.

Species Significance

Historically, oystercatchers were hunted for both culling and recreational purposes, causing a near extinction along the Atlantic coast. Their breeding success worldwide has been low. This reflects mortality rates during the egg stage, rather than the mortality of dependent chicks. Predators and storms are the main cause of egg loss from the nest. However, the population decrease may also be attributed to the exploitation of shellfish resources by man, coastal development, and off-road vehicles destroying natural habitats. Their numbers have recently increased due to the implementation of protection programs. Oystercatchers are now common in areas where they were absent a few years ago.

References

Bull, J. L. and J. Farrand, Jr. 1995. National Audubon Society Field Guide to North American Birds. Eastern Region. The Audubon Society field guide series. Alfred A. Knopf Inc., New York, NY.

Goss-Custard, J. D. (ed.). 1996. The oystercatcher: From individuals to populations. Oxford University Press, Oxford, U.K.

Nol, E., A. J. Baker, and M. D. Cadman. 1984. Clutch initiation dates, clutch size, and egg size of the American oystercatcher in Virginia. The Auk 101:855-867.

Sprunt, A., Jr. and E. B. Chamberlain. 1970. South Carolina bird life. University of South Carolina Press, Columbia, SC.



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