An adult American oystercatcher |
A juvenile beside Herring gulls |
This bird species is interesting enough to have attracted admirers, researchers, and advocates into a flock called the American Oystercatcher Working Group (AOWG). Their website is the only reference I've found to apply the wonderful descriptor 'pied'. It calls to mind patchy-patterned mustangs running wild on Chincoteague Island in Virginia which is in the central part of the oystercatcher's range.
Oystercatchers typically gravitate to sandy or gravelly beaches where they can probe for submerged food at the tide line. When it locates a shellfish with open valves, an oystercatcher quickly inserts its bill to sever the adductor chain that holds the halves together. It then extracts and consumes the soft parts.
Less
commonly oystercatchers visit rocky shores such as Halibut Point. They pick
individual mussels from a clump, hammer them to break through the shell, once
again severing the adductor muscle to open the halves and consume the soft
parts of the shellfish.
Their large size and white wing band make oystercatchers conspicuous in flight. They are also very vocal when alerted to danger, so you may hear them before you see them. Most likely they will see you first.
The species was hunted
to near extinction in the 19th century for plumage and eggs. It has recovered
significantly since the passage of the Migratory Bird Treaty Act in 1918 and
has begun returning to its former range from refuges in the mid-Atlantic
states. Oystercatchers reached coastal Massachusetts in 1969 and are occasionally
seen as far north as Nova Scotia.
Adult (L) and juvenile (R) |
The photograph confirms
that oystercatchers are successfully breeding in Massachusetts. As the
juveniles reach full size they closely resemble adults, with slightly duller plumage and
grayer bills. Their eyes have not yet developed the bright orbital rings.
The AOWG offers some
interesting observations about the birds' survival adaptations:
-Their counter-shaded plumage blends in
surprisingly well in feeding habitat, particularly mussel and oyster beds, as
well as on breeding habitat.
-The young can be heard calling from within the egg
two days before they hatch.
-When eggs are present, at the approach of
predators or humans, the tending adult slips off nest, usually unseen, while
the intruder is still some distance away. It walks rapidly away some distance
before taking flight. The bird then exhibits distraction behavior, circling back
over the intruder in “butterfly” flight giving distress calls. It often adopts a
mock sleeping attitude or mock brooding in an exposed location. In this posture
it may allow predatory birds such as gulls to approach and rarely even touch it.
Once displaced, the oystercatcher will run some distance, then resume mock
brooding posture again.
- Precocial chicks are able to stand upright and run short distances
within hours of hatching. They respond to parent alarm calls by running for
cover, then lying immobile. Often they will not move until picked up. As
fledglings they can escape gulls and peregrine falcons by diving under water,
propelling themselves with their wings.
By late summer the oystercatchers begin their return to wintering
grounds on the southern shoreline of the United States. They are a bellwether
species of healthy coastal environments. We can hope that they will find our
region increasingly appealing.
The oystercatchers have been nesting on Thacher Island. Two nesting pairs have been observed on the island for the past two years, with 1-2 chicks per pair. Their eggs, laid in shallow depressions in the rocks, are almost impossible to see. In fact, the adults themselves are almost impossible to see when they are at rest on the rocks, which is surprising given that their most recognizable feature is that big orange beak. What is recognizable is their call, which is a lovely tin-whistle trill.
ReplyDeleteWow,Martin! I think Kim Smith posted seeing the big O this summer.
ReplyDeleteI saw my 1st. bunch in Chinkateague back in the 70's, & occasionally in the back of Crane's beach more recently. They are stunning birds.
And thanks for for all the background.