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Black Oystercatcher
Haematopus bachmani
Black Oystercatcher
Foraging, Feeding & Hunting Behaviour
Black
Oystercatchers prey on marine
invertebrates found on rocky shores, gravel beaches and mudflats
along the seashore. The chisel-shaped bill is used to pry limpets,
chitons and snails from rocks, sever muscles in clams and muscles,
and chip holes in hard shells. Mussels are eaten by inserting the
bill into a gape between the shells, severing the muscle, and
tearing out the flesh. Black Oystercatchers rarely live alongside
oysters but they are known to chip openings into shells and remove
the flesh in the same fashion as they eat mussels. They also
scavenge pieces of oyster from shells discarded by oyster farmers.
Little is known about their foraging habits on gravel and sandy
beaches when these habitats are frequented outside the breeding
season. Foraging time is dictated by the tides since all their food
is found on the beaches.
Black Oystercatcher
Flight
Patterns
Black
Oystercatchers fly with powerful and steady wingbeats often in
straight and steady flight. They often fly in small groups and
rarely fly at high altitude.
Aggressive, Defensive & Territorial
Displays of the Black Oystercatcher
Displays used by oystercatchers have been described for the breeding
season. Threats often begin with a piping call when a territorial
bird first sights the approach of another oystercatcher. The neck is
outstretched and the bill is lowered slightly. This rigid upright
stance is interrupted by a forward lowering of the head and bill as
the threat gains intensity. This display is often met with similar
intensity by neighbouring pairs at the boundary of the territory.
Oystercatchers that fly toward a territory are usually met in flight
and escorted far away by territorial pairs. The territorial
oystercatchers will sometimes slow the wing beat to enhance the
display.
Courtship & Breeding Behaviour of the
Black Oystercatcher
The
breeding season begins in May in the south and June in the north,
and extends into August and September. Oystercatchers produce 1
brood per year but will relay a clutch if the first
attempt fails early in the season. Many oystercatchers nest with the
same mates each year on the same territory and often in the same
nest. Finding an empty nesting territory is often difficult for
oystercatchers because very few islands have sufficient food, safety
from land predators, and suitable nest sites, and oystercatchers are
long-lived birds. The result is that a surplus of breeding age
oystercatchers to quickly fill any opening.
Mated
pairs work together to defend a territory from other oystercatchers
although males do most of the defending. A nest will be built in the
territory that includes an area about 10-50 m on either side of the
nest. Oystercatchers copulate following a long display of piping
calls, prancing about the territory and raising and lowering of the
head and bill. The male holds his neck erect with the bill pointed
down while the female crouches and gives churring calls. He climbs
on to her back, bends his legs and moves his tail until his cloaca
touches hers. He then leaps from her back and the pair stands, wag
their tails and begin to preen.
Nesting Habits of the Black
Oystercatcher
Most
oystercatchers breed in association with Glaucous-winged Gulls on
coastal rocky islets, jetties and breakwaters. Shorebird
biologists estimated the world’s breeding population to be about
10,000 pairs of which most pairs are in Alaska, followed by British
Columbia, Washington, Oregon, California and Baja California. The
nest is characterized by a few shells or rock fragments, or a
depression in sand and pebbles just above the high tide line. Eggs
are ivory with a faint green hue and chocolate coloured scrawl
markings. The average clutch size in Alaska and British Columbia was
about 2 eggs. Adults will pretend to have a broken wing or sit on a
nest where none is present when an intruder approaches a nest. They
will also utter ear-piercing shrieks and fly in front of intruders
who get close to their young.
Incubation
requires about 26-28 days. Eggs hatch into downy chicks with salt
and pepper markings, dark brown irises and black legs. They are fed
by both parents a diet of marine invertebrates caught along the
shore near the nest or on neighbouring islands. As the chicks age,
their downy feathers are replaced with blackish or dark brown flight
feathers. The bills of young oystercatchers are characteristically
reddish orange with a dark tip. It will take 6 months or more to
attain the red bill of the adult. The first flight takes place about
40 days after hatching.
Vocalizations and Calls of the Black
Oystercatcher
Among
the many vocalizations given by oystercatchers, the call most often
heard signals their threatening intentions. The piping whistled
pew, pew pew call is given when they are anxious or wish to
threaten other oystercatchers. The shrill call rings out over
nesting islands day and night. Oystercatchers also utter a subdued
chirping call when they are preparing to mate.
Video - Oystercatcher call
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