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Black Oystercatcher
Haematopus bachmani
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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