A Sighting at the Shore
by Lynn Morgenstern
O
n a typical Kiawah beach walk, when one
is expecting to pass a phalanx of indistinguishable,
monochromatic, buff and beige shorebirds, it can come
as a surprise to see a bird that so clearly stands out from
the crowd: the American oystercatcher (Haematopus
palliatus). With its black head, brown back and wings, and
white stomach and chest, this bird would almost look like a
species of sea gull were it not for its large, bright orange bill
and its orange-encircled, yellow eyes, which give it a wildeyed, somewhat comical appearance. (Juveniles differ only
in the duller brown color at the tip of their bill and brown
eyes.) Oystercatchers are, in fact, the heaviest American
shorebirds, weighing 1.4 pounds and measuring between
16 and 17½ inches in length with a wingspan of up to 32½
inches; and a beach is a likely place to find them.
Oystercatchers frequent sand and shell beaches,
intertidal mudflats, shell rakes, salt marshes and islands made
of dredge spoil. While many of the oystercatchers seen on
Kiawah are year-round residents, during colder months, the
area also hosts migrants from coastal areas north of New
Jersey and sometimes as far south as the north coast of
South Carolina. [The South Carolina Department of Natural
Resources (SCDNR) reports that it found a bird on Kiawah
that had been banded in McClellanville.] For oystercatcher
migrants, the trip to South Carolina begins in the fall and
continues through early March. Of particular note, according
to the 2007 American Oystercatcher Conservation Plan the
South Carolina coast is the “heart of the oystercatcher’s
winter range.”1 This is because over one-third of the
Atlantic and Gulf coast population of oystercatchers winter
here. The oystercatchers are very social during this time,
often gathering in flocks of over 100 birds.
In the spring, after migrants return home,
the resident population begins breeding and nesting.
Oystercatchers typically mate for life and engage in
courtship behavior, such as walking or flying side-by-side
while emitting particular calls. Typically, it is the male
oystercatcher that creates the nest, a mere depression
scraped into the sand. The female will lay two to four eggs
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sometime between early April and late June. These eggs
will hatch within 24-27 days. Both parents care for the
young, and, unlike other shorebirds, oystercatcher chicks
require parental care for at least an additional month after
they fledge. During the two month period after hatching,
the parents feed their young and teach them how to obtain
food on their own. Many researchers believe that, in the
first year, young oystercatchers winter with their parents
before feeding entirely on their own.
Feeding is highly specialized, since oystercatchers
are either “stabbers” or “hammerers.” Stabbers use their
large, heavy bill, frequently described as flattened like a
chisel, to attack a bivalve, such as an oyster or mussel, just
as it opens its two shells to take in water. The oystercatcher
rams its bill between the shells, forcing the tip of its bill
straight to the adducter muscle in the rear which holds the
two shells together. The bird uses the tip of its bill to sever
the muscle, causing the bivalve to fall open and expose the
tasty meat inside. Hammerers use their bills to pound the
shell of their prey until it breaks open. In a test of nature
versus nurture, scientists moved a hammerer’s eggs into
the nest of stabber and vice versa. The result was that
the stabber still raised stabbers and the hammerer chicks
also behaved like their adoptive parents, demonstrating
that each feeding approach was a learned behavior.2 In
addition to bivalves, oystercatchers eat other small marine
invertebrates, such as worms and crabs.
Clearly, the habitat necessary to maintain
populations of oystercatchers is a limited one, since, each
year, less and less pristine coastal environment is available,
not only for feeding, but also for nesting and roosting
as well. Oystercatchers return to the same nesting sites
year after year and are very territorial during the breeding
process. Thus, the loss of nesting sites places stress on
breeding pairs and hatchlings. While internationally the
American oystercatcher is not considered to be in serious
danger, the oystercatcher is designated as a species
of “extremely high priority” in North America. The
Conservation Action Plan, previously cited, points to the