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Black Oystercatcher Haematopus bachmani

Black Oystercatcher

The Black Oystercatcher is a conspicuous Pacific Coast endemic shorebird that resides from Baja California to 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. Andres and Falxa (1995) wrote a comprehensive review of the biology of the species.

 

Population size

The current world population estimate is thought to be between 6900 and 10800 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.

 

Breeding biology

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 behaviour 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.

 

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 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). 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 defence of nesting sites likely delays some otherwise sexually mature oystercatchers from finding a suitable site to nest. It shows very strong fidelity to nesting territories (Hazlitt and Butler 2001).

 

Oystercatcher chicks hatch with downy salt and pepper coloured feathers that they wear for the first few weeks until the juvenal feathers emerge. Their legs and bills are dark brown to black in colour and the eye is dark. Juvenals have dark brown almost black feathers fringed with buff on the mantle and wing. The iris is brown and the legs are dark brown or yellowish. In their first winter, oystercatchers resemble a paler version of the parent. The bill is reddish or orange with a dark brown tip. It will carry this plumage until it is about 12-13 months of age when it will attain the full adult breeding plumage. Adults moult their feathers in late summer (Paulson 1991). Oystercatchers probably begin to breed in their third summer at the earliest (Paulson 1991).

 

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.

 

Post-breeding Biology

Considerably little is known about the post-breeding biology of the oystercatcher. Some oystercatchers frequent small islets and islands and spend time on shores not used during the breeding season. Marked immature oystercatchers have been sighted about 60 kilometres from where they were born but not much is known about dispersal. Flocks in Alaska and British Columbia gather in bays sheltered from winter storms to eat mussels (Hartwick and Blaylock 1989, Andres 1998). Alaskan oystercatchers return to nesting area in March and depart in September (Andres 1998).  Some examples of large flocks are 65 in Tofino in May 1931, 96 in Victoria in November 1962, 60 at Sidney in October 1965, 106 on Cleland Island in July 1970, and 74 on Malcolm Island in 1976 (Campbell et al. 1990).

 

References

 

Ainley, D. G. and T. J. Lewis. 1974. The biology of Fallaron Island marine bird populations – 1854-1972. Condor 76:432-446.

 

Andres, B. A., and G. A. Falxa. 1995. Black Oystercatcher (Haematopus bachmani). In The Birds of North America, No. 155 (A. Poole and F. Gill, eds.). The Birds of North America, Inc., Philadelphia, PA.

 

Andres, B. A. 1998. Oystercatcher. Restoration Notebook. Exxon Valdez Oil Spill Trustee Council. (on line).

 

Butler, R. W. and J. W. Kirbyson 1979. Oyster predation by the Black Oystercatcher in British Columbia. Condor 81: 433-435.


Campbell, R.W., N. K. Dawe, I. McTaggart-Cowan, J. M. Cooper, G. W. Kaiser, and M. C.

E. McNall. 1990. The birds of British Columbia. Volume 2. Royal British Columbia Museum, Victoria.

 

Groves, S. 1984. Chick growth, sibling rivalry and chick production in American Black

Oystercatchers. Auk 101:525-531.

 

Hartwick, E. B. 1974. Breeding ecology of black oystercatchers (Haematopus bachmani Audubon).

Syesis 7: 83-92.

 

Hartwick, E. B. and W. Blaylock. 1979. Winter ecology of a Black Oystercatcher population. Studies in Avian Biology 2:207-215.

 

Hazlitt, S. L. 1999. Territory quality and parental behaviour of the Black Oystercatcher in

the Strait of Georgia, British Columbia. Unpubl. MSc thesis, Simon Fraser University, B.C.

Hazlitt, S.L. 2002. Territory quality and reproductive success of Black Oystercatchers in British Columbia. Wilson Bulletin 113:404-409.

Hazlitt, S.L. and R.W. Butler. 2001. Site fidelity and reproductive success of Black Oystercatchers in British Columbia. Waterbirds 24:203-207.

Hazlitt, S.L., R.C. Ydenberg and D.B. Lank. 2002. Territory structure, parental provisioning and chick growth in the Black Oystercatcher (Haematopus bachmani). Ardea 90:219-227.

Nysewander, D. 1977. Reproductive success of the Black Oystercatcher in Washington State. MSc thesis, University of Washington, Seattle.

Rodway, M.S. 1991. Status and conservation of breeding seabirds of BritishColumbia. Pp. 43-102 in Croxall, J.P. (ed.) Seabird status and conservation: a supplement. ICBP Technical Publication No. 11.

Vermeer, K., K. H. Morgan, and G. E. J. Smith. 1989. Population and nesting habitat of

American Black Oystercatchers in the Strait of Georgia. Pp. 118-122 in K. Vermeer

and R. W. Butler (eds.). The ecology and status of marine and shoreline birds in the

Strait of Georgia, British Columbia. Canadian Wildlife Service Special Publication, Ottawa.

 

Wootton, J. T. 1992. Indirect effects, prey susceptibility, and habitat selection: impacts of

birds on limpets and algae. Ecology 73:981-991.

 

Black Oystercatcher Project

To Tlingit shaman inhabiting the northwest shores of North America, the oystercatcher inhabiting the border world between water and land was in parallel with the shaman's role between the human and spirit worlds. The oystercatcher is depicted on rattles used by Tlingit shaman.

The aim of the PWLF in collaboration with Parks Canada’s Gulf Islands National Park Reserve is to investigate whether the oystercatcher is a suitable species to measure the impact of human disturbance on the ecology of rock islands. Oystercatchers play an important role in rocky shore intertidal communities as predators of small marine invertebrates. They are largely confined to nest on small rocky islets away from most predators. Oystercatchers on islands near urban centres are frequently disturbed by kayakers and boaters.  Oil spills can harm oystercatchers.

 

The objective of our study is to establish a means to measure human impacts on oystercatchers. The first step is to understand the causes of nesting variation under natural conditions. On the exposed outer coast of British Columbia, storms that wash out nests is an important natural event. On the inner coast where large waves from storms are less of a problem, the causes are attributable to whether oystercatchers are in good or poor nesting territories. Good territories have low shelving slopes or reefs with invertebrate prey where the young can follow the parents. Poor territories are steep sloped with few invertebrates and where parents must fly food to their young. Once we have clarified the natural causes of nesting variation, we can remove the effects and go on to measure human impacts.

Current PWLF Projects

 

 
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