Oystercatchers

(Haematopodidae)

Class Aves

Order Charadriidae

Suborder Recurvirostrinae

Family Haematopodidae

Thumbnail description
Medium to large-sized, stocky waders with distinctive dark and light plumage, blunt-tipped dagger-like reddish bills, red to yellow eyes, and pink legs

Size
15.8–19.8 in (40–49 cm); 0.88–1.54 lb (400–700 g)

Number of genera, species
1 genus; 7 species

Habitat
Rocky and sandy shores, marshes, tidal mudflats, estuaries

Conservation status
Endangered: 1 species; Near Threatened: 1 species

Distribution
North America, Europe, Africa, East Asia, Australia, New Zealand

Evolution and systematics

The number of species within the genus Haematopus (oystercatchers) has been in dispute since its designation. Five species and seventeen subspecies were recognized through the 1970s. As of 2001, this list had been expanded to include as many as 14 species; 11, however, are generally accepted according to Sibley and Monroe. One of these, the Canary Islands oystercatcher (Haematopus meadewaldoi), has not been reported since the 1940s and is considered extinct.

The fossil record for oystercatchers is spotty. Morphological differences between New and Old World taxa, along with a distribution heavily tilted toward the Southern Hemisphere, suggest that the group originated in the paleocontinent of Gondwana and was split with the departure of the South American landmass. Two early Pliocene specimens have been reported in North America: the oldest fossil species, H. sulcatus, from the Bone Valley Formation (Palmetto Fauna), Florida, and a second record of Haematopus sp. from the Yorktown Formation at Lee Creek, North Carolina.

Physical characteristics

The similarities in appearance among oystercatcher species help explain the family's disputed taxonomy. Apart from differences in eye color between Old and New World taxa, all black oystercatcher taxa have completely dark plumage. Pied taxa in both regions have dark upperparts, head, neck, tail, and upper breast, white lower breast, belly, and uppertail coverts, and white bars on the upper wing. Variable oystercatchers (H. unicolor) are unique among waders in their polymorphism. Slightly fewer than three-quarters of variable oystercatchers are black and another 20% are pied. The rest fall somewhere in between and are known colloquially as "smudgies." Pied morphs tend to be smaller than their black counterparts, but in this aspect variable oystercatchers are once again unique; black morphs of this species are on average lighter than are pied morphs.

Oystercatcher females are heavier and have longer wings and bill than males. Otherwise, wing length is very similar among species. Immature oystercatchers have buffy margins on their dark feathers and duller colors on the eye rings, legs, and bill.

Elongated and thickest near the tip, the distinctive bill of an oystercatcher is often described as blade-like or dagger-like, an image intensified by its red or orange color. Haematopus, meaning "blood eye" in Greek, denotes the scarlet eye and eye ring found on Old World oystercatchers. New World taxa have yellow irises and orange-red or yellow eye rings.

Distribution

Oystercatchers inhabit coasts worldwide and lake shores inland in the Palearctic and New Zealand. Nine species occur in the Southern Hemisphere; none of these migrate significantly, although their ranges do overlap. Two species occur in Australia, New Zealand, and western South America, and three coincide in parts of southern South America. In both cases, black or polymorphic species specialize on rocky shores, whereas pied species stake out softer substrates or forage inland.

Oystercatcher ranges vary widely. American oystercatchers (H. palliatus) are found along the coasts of North and South America from Patagonia to the Gulf of California and Massachusetts, as well as the West Indies. Their Old World counterpart, Eurasian oystercatchers (H. ostralegus), range from western Europe, Scandinavia, western Russia (including the Black, Caspian, and Aral seas), and North Korea to winter habitats on the coasts of East Africa, Arabia, India, and eastern China. In contrast, Chatham Islands oystercatchers (H. chathamensis) are restricted to the Chatham Islands east of New Zealand.

Habitat

Oystercatchers primarily inhabit shorelines of every type, from rocky shores to beaches of sand, pebble, and shell. Salt marshes, estuaries, and coastal lagoons are also suitable habitat. A few species occur inland in areas of low vegetation or on agricultural land and pastures. Most oystercatchers found inland are soft-substrate specialists, drawn by freshwater bodies of all sizes. Two races of Eurasian oystercatchers breed inland in the Palearctic, some around the Black and Caspian Seas. South of the equator, inland breeders include Magellanic oystercatchers (H. leucopodis), the South Island race of the Eurasian oystercatcher (H. o. finschi), and, infrequently, the Australian pied oystercatcher (H. longirostris).

Habitat switching, particularly between the breeding and nonbreeding season, is the norm rather than the exception among oystercatchers. Pied taxa often return to rocky coasts in the winter, as in the case of Magellanic oystercatchers and American black oystercatchers (H. bachmani). Among all-black species, blackish oystercatchers (H. ater) exhibit similar behavior, whereas American oystercatchers seek out mudflats in winter. Eurasian oystercatchers, American black oystercatchers, and sooty oystercatchers (H. fuliginosus) tend to winter on softer substrates such as those associated with estuaries.

Behavior

Oystercatchers demonstrate strong fidelity to both mates and breeding sites. Migratory species such as Eurasian oystercatchers return to the same locations from year to year. Young return to breed close to where they were hatched, often from hundreds of miles away. All oystercatchers defend breeding territories, and some species exhibit year-round territoriality.

Other species, such as African black oystercatchers (H. moquini), form high-tide roosts to defend against predators and keep warm in cold climates. Foraging flocks most often have fewer than 50 members (black taxa seldom gather in groups of more than 10), but groups of over 1,000 inland breeders, such as Australian pied oystercatchers and some races of Eurasian oystercatchers, occasionally gather.

Only Eurasian oystercatchers are truly migratory, with three Palearctic races that fly as far as 30°s in winter. These birds may double their body mass in preparation for the journey. In their northern extents of their ranges, American oystercatchers and American black oystercatchers also move south in winter.

Oystercatcher calls are simple, sharp, and loud peeps, often starting out with a rapid, brief trill that becomes progressively longer.

Feeding ecology and diet

Oystercatchers depend on a wide range of marine invertebrates for food. Bivalve mollusks of several species are dominant

prey items, but oystercatchers also eat crabs, chitons, sea urchins, whelks, snails, and an occasional fish. Variety is key; African black oystercatchers are known to eat at least 52 species. Arthropods are the main food source inland.

Oystercatchers exhibit an impressive range of techniques to overcome the often substantial defenses of their prey. When an oystercatcher finds a feeding mussel with its shell slightly open, the oystercatcher quickly stabs its bill inside to sever the muscle connecting the valves before cleaning out the flesh inside. (Oystercatchers have been known to drown with incoming tides after their bills became caught by shell-fish.) The bird's narrow bill fits through small openings, and a concentration of nerve endings near the tip help locate prey in muddy waters.

American oystercatchers infrequently hammer mussels against rocks to crack the shell, and American black oystercatchers will pry limpets off rocks to eat. Eurasian oystercatchers use their long bill to extract lugworms (Arenicola marina) from their U-shaped tubes in intertidal flats. Regardless of technique, oystercatchers can often catch prey faster than they can digest it.

Reproductive biology

All oystercatchers are predominantly monogamous and breed in summer. During the "piping" courtship display, two birds utter a single piped note while walking, running, or flying closely parallel, turning often. This display may be joined by nearby pairs for a piping "tournament" and is also used as a mate greeting or territorial display. Breeding Magellanic oystercatchers cock the tail skyward to reveal pure white undertail coverts.

Clutches can be one to four eggs but are most often two or three; rarely, Eurasian oystercatchers produce five eggs. Oystercatcher nests are scrapes on the ground that may be lined or unlined. First eggs are often undertended and lost (up to 40% among Eurasian oystercatchers), and parents incubate alternately and continuously for 24–39 days. The eggs are spotted gray with bluish or buffy tints, and blend in well on pebbly surfaces. Oystercatcher chicks are the same dull gray-brown as their surroundings and unique in being fully mobile within a day of hatching. Old World taxa have crowns marked conspicuously with black, while New World taxa (and the Magellanic oystercatchers) do not. Oystercatcher parents feed their chicks, who can run and hide from danger, until well after fledging, which is at least 60 days after hatching in the case of American oystercatchers. This strategy minimizes the risk of predation while maximizing the high growth rates of parent-fed young. Nevertheless, average rearing success is usually less than one chick per pair per year. Storms and predators pose the greatest risks to oystercatcher eggs and chicks, respectively.

Conservation status

As a whole, oystercatchers are doing well; as of 2001, only three species numbered less than 5,000 individuals. Introduced predators and human disturbance both take a significant toll on eggs and chicks. The total population of African

black oystercatchers was estimated at 4,800 birds in the early 1980s, earning the species Lower risk/Near Threatened status. Coastal recreation, including off-road vehicles, disturbs or destroys nests or causes parents to flee, leaving eggs vulnerable to overheating or natural predation. Populations on near-shore islands, however, have stabilized or increased due to improved management. Chatham Island oystercatchers number only 100–150 individuals and are classified as Endangered. Limited to four small islands in New Zealand, the species appears to have increased significantly in the 1990s, thanks to conservation efforts that include predator removal and artificial incubation. Fluctuating population levels, however, ensure the species' situation remains precarious.

Significance to humans

Aside from unsubstantiated reports of oystercatchers preying on commercial oyster beds and frequent comments on the birds' somewhat comical appearance, oystercatchers have no particular significance to humans.

Species accounts

List of Species

American oystercatcher

Haematopus palliatus

taxonomy

Haematopus palliatus Temminck, 1820, Venezuela. Two subspecies.

other common names

English: American pied oystercatcher; French: Huîtrier d'Amérique; German: Braunmantel-austernfischer; Spanish: Ostrero pio Americano.

physical characteristics

15.75–17.32 in (40–44 cm); male averages 1.25 lb (567 g), female 1.41 lb (638 g). Black head, neck, upper breast, tail, flight feathers; white belly and lower breast; orange-red bill and eye ring; yellow eye. Only pied oystercatcher with brownish dorsal plumage. Juveniles have dark eyes, inconspicuous eye ring, dark tip on bill, and the upperparts are fringed with buff.

distribution

Coastal Americas from Gulf of California to Chile, southern Argentina to Massachusetts, West Indies. H. p. galapagensis occurs only in Galapagos Islands.

habitat

Sandy, shell, and pebble beaches, salt marshes, rocky shores.

behavior

Territorial, sometimes moves to mudflats in winter.

feeding ecology and diet

Takes snails, oysters, crabs, mussels, and clams using a variety of techniques. On rocky shores in Panama feeds almost entirely on mollusks.

reproductive biology

Breeds only at the coast. Known to hybridize with blackish oystercatchers in South America and American black oystercatchers in western Mexico and Gulf of California (the latter resulting in disputed race H. p. frazari). Chick plumage consists of drab upperparts, white underparts, and dark stripes on sides and back. Breeding occurs during a two-month breeding season over range, ranging from February to October.

conservation status

With a total population of about 5,000 birds, generally not considered globally threatened, but sometimes considered Near Threatened.

significance to humans

None known.

African black oystercatcher

Haematopus moquini

taxonomy

Haematopus moquini Bonaparte, 1856, Cape of Good Hope. Monotypic.

other common names

English: African oystercatcher, black oystercatcher; French: Huîtrier de moquin; German: Schwarzer austernfischer; Spanish: Ostrero negro Africano.

physical characteristics

16.54–17.72 in (42–45 cm); 1.28–1.67 lb (582–757 g), females 1.42–1.76 lb (646–800 g). Dark overall with vermilion bill and eye ring, red eye, and pink legs. Females have noticeably longer bills.

distribution

Coastal southern Africa from northern Namibia to Cape of Good Hope and east to Natal.

habitat

Sandy and rocky shores, offshore islands, occasionally estuaries and coastal lagoons.

behavior

Territorial, relying on camouflage on dark rocky substrates. Sedentary adults rarely disperse as far as juveniles; most often less than 100 mi (160 km) in any case.

feeding ecology and diet

Eats limpets, mussels, whelks, and polychaetes in rocky areas, wider range of prey on sandy substrates but favors sand mussels.

reproductive biology

Usually breeds on offshore islands and sandy beaches, laying one to two eggs between October and April. Eggs are greenish or buff with dark brown spots. Eggs and young are vulnerable to terrestrial mammalian predators, although young are well camouflaged. The chick plumage is gray with black stripes on back and sides.

conservation status

Considered Near Threatened as of 2001, with a total population of about 5,000 birds. Major threats are introduced mammalian predators on island populations, followed by human disturbance on sandy beaches.

significance to humans

None known.

Variable oystercatcher

Haematopus unicolor

taxonomy

Haematopus unicolor J.R. Forster 1844, New Zealand. Pied morph occasionally considered separate species (H. reischeki) or race.

other common names

English: New Zealand black oystercatcher, New Zealand sooty oystercatcher, northern oystercatcher; French: Huîtrier variable; German: Neuseeländischer austernfischer; Spanish: Ostrero Variable.

physical characteristics

18.50–19.29 in (47–49 cm); male averages 1.49 lb (678 g), female 1.59 lb (724 g). Only oystercatcher species with black and pied morph. Dominant morph is black overall with red eye, bill, and eye ring; pied morph has white breast, belly, back, and small wingbar. Frequent intermediate morphs are larger overall and are called "smudgies."

distribution

Coast and islands of New Zealand.

habitat

Rocky and sandy shores.

behavior

Territorial and sedentary, occasionally flock in harbor and estuaries.

feeding ecology and diet

Feeds on sandy beaches and rocky shores. Varied diet includes crabs, gastropods, bivalves, and polychaetes.

reproductive biology

Frequent interbreeding between morphs. Breeds from December through January (occasionally as early as September) on dunes and sandy beaches. Clutches are most often three eggs incubated for 25–32 days. Chicks of black morph have dark underparts and crown, while those of pied morph have white breasts and grayish-brown upperparts.

conservation status

Not considered threatened, even though total population is estimated at 3,900 birds. Threats include human disturbance and mammalian predation, but several populations were increasing in 1980s and 1990s, especially on North Island where over two-thirds of variable oystercatchers reside.

significance to humans

None known.

Resources

Books

BirdLife International. Threatened Birds of the World. Barcelona: Lynx Edicions, 2000.

Hayman, P., J. Marchant, and T. Prater. Shorebirds: An Identification Guide to the Waders of the World. London: Croom Helm, 1985.

Hockey, P.A.R. "Family Haematopodidae (Oystercatchers)." In Handbook of the Birds of the World. Vol. 3, Hoatzin to Auks, edited by J. del Hoyo, A. Elliott, and J. Sargatal. Barcelona: Lynx Edicions, 1996.

Marchant, S., and P.J. Higgins, eds. Handbook of Australian, New Zealand, and Antarctic Birds. Vol. 2, Raptors to Lapwings. Melbourne: Oxford University Press, 1993.

Nol, E., and R.C. Humphrey. "American Oystercatcher (Haematopus palliatus)." In The Birds of North America. Vol. 3, edited by A.F. Poole, and F.B. Gill. Philadelphia: Academy of Natural Sciences and American Ornithologist's Union, 1994.

Periodicals

Hockey, P.A.R. "Aspects of the Breeding Biology of the African Black Oystercatcher." Ostrich 54 (1983): 26–35.

Hockey, P.A.R. "The Distribution, Population Size, Movements, and Conservation of the African Black Oystercatcher Haematopus moquini." Biological Conservation 25 (1983): 233–262.

Julian Smith, MS