Black Oystercatcher

By Archives •  Updated: 07/05/22 •  7 min read

The Black Oystercatcher (Haematopus bachmani) is a distinctive Pacific Coast shorebird that resides from Baja California to the western Aleutian Islands. Its nesting habitat is the rocky islands and islets along the Pacific Coast of North America.

Some oystercatchers choose to remain near their nests all year round but others gather into flocks in bays sheltered from the wind and storms. The black oystercatcher is the only representative of the oystercatcher family (Haematopodidae) over most of its range, overlapping slightly with the American oystercatcher (H. palliatus) on the coast of Baja California.

Oystercatchers often are heard before they are seen. Their loud whistling wheep-wheep is shrill and carries above the sound of the surf. They also utter a softer more rapid repeated hew-hew-hew-hew call when they are becoming alarmed.

Population

Black Oystercatcher (Haematopus bachmani)

Black Oystercatcher (Haematopus bachmani) Credit: Ingrid V Taylar CC-BY

Current world population is estimated to be between 6,900 and 10,800 individuals (Andres and Falxa 1995). The distribution is nearly continuous across the range with about half of all oystercatchers occurring in Alaska, slightly less than half in British Columbia, a few hundred in Washington State, and a few hundred in Oregon, California and Baja California.

The species is scarce along the sandy outer coasts of Washington and Oregon and it possibly interbreeds with the American Oystercatcher in Baja California (Nysewander 1977, Paulson 1991, Andreas and Falxa 1995). The population estimates are based on data collected by many biologists using a variety of methods and across several years.

In British Columbia, the estimate is based upon the number of oystercatchers counted during censuses of seabirds (Rodway 1991). Vermeer et al. (1989) visited over 200 potential nesting islands in the Strait of Georgia, British Columbia, and tallied only 67 pairs of oystercatchers.

Hazlitt (1999) made multiple visits to a sample of the same nesting islands in the southern Gulf Islands to show that a single visit detected only 68% of the number of oystercatchers that were present. These results suggest that the tally by seabird biologists likely underestimated the true number of oystercatchers in British Columbia.

Feeding Habits

Oystercatchers will eat oysters when given an opportunity (Butler and Kirbyson 1979) but most eat limpets, clams, snails, and chitons. They stab partly opened mussels and clams, pry limpets from the rocks, or hammer a hole in the shells of oysters (Butler and Kirbyson 1979).

Oystercatchers are dependent on a steady supply of small intertidal invertebrates as food. The predatory impact of oystercatchers plays a role in determining the presence and abundance of their prey (Wootton 1992).

Black Oystercatcher Breeding Behavior

Oystercatchers in the Georgia Basin nest on small rocky islets, spits, and islands with shallow sloping intertidal shores or nearby reefs where they can find food. The breeding season is characterized by strong territorial behavior toward other oystercatchers around nests and nearby foraging sites.

Nests are located in the territory and just above the high tide line on bare rock, in shells, gravel, sand, or tufts of grass, and among logs. Most nests are shallow scrapes in shell fragments or gravel but some are built in grass or on bare rock.

Typically two or three egg clutches are laid in a clutch in May and June – 310 clutches in British Columbia had a mean of 2.04 eggs (SD 0.66; Hartwick 1974). Both parents incubate the eggs and most eggs hatch 26-28 days late in late June and July. Chicks are brooded by the parents nearly continually in the first few days after hatching.

Young oystercatchers are precocious which allows them to accompany their parents into the intertidal portion of beaches in search of food. Those pairs that nest on shallow sloping islands escort the young to the beach where they are fed.

Pairs nesting on steep sloping beaches are unable to escort their young so the parents must transport the food to them (Hazlitt et al. 2002). As a consequence, pairs nesting on steep sloped islands raise fewer young on average than pairs on shallow sloped islands.

Young oystercatchers are capable of flight beginning about late July or when they are about 40 days old. Survival to 1-2 years was not affected by the weight of fledglings just before they could fly (Groves 1984). Age at first breeding is not known and strong territorial defense of nesting sites likely delays some otherwise sexually mature oystercatchers from finding a suitable site to nest. It shows very strong fidel