Oystercatchers abound in Southeast

Birds liven up our shoreline, but they don't catch oysters

Posted: Sunday, July 07, 2002

Wheee-whee-whee-whee! Some time when you're trolling, drifting or paddling through Southeast's inland waters you may be startled by a series of loud, high-pitched, whistle-like calls.

Look carefully along the shoreline, especially on small, rocky islands and you will see the sound is coming from a large black shorebird about the size of a crow with a long, straight, orange-red bill. Even from some distance you may be able to see its legs and feet are pinkish, and its bright yellow eye is surrounded by a red ring.

It's a black oystercatcher.

We see oystercatchers quite often in Southeast Alaska, though their population here is not large. They are most noticeable at low tide, when they patter officiously along the mid-tidal level, foraging for - not oysters - but mussels, limpets, chitons and clams. They may also eat crabs, sea urchins, barnacles, polychaete (segmented) worms and occasionally small fish.

The oystercatcher's bill is a remarkable tool. Up to 3 1/2 inches long, it is flattened laterally at the tip like a chisel.

The birds can use it to dislodge limpets and chitons from rocks, then flip them over and extract the soft tissue beneath the shell. They can jab it between the open shells of mussels and clams (open because the bivalves are feeding), sever the adductor muscle, then eat the soft meat inside. They can use it to turn over sea urchins or crabs, then extract the meat through the soft underside.

Young oystercatchers apparently need a fair amount of time to develop these specialized feeding techniques. Even when they are nearly 2 months old, chicks may depend on their parents for more than half their food, and most chicks don't feed well enough to leave their parents during their first winter. One study showed that immature birds took more than three years to develop a complete repertoire of efficient foraging skills.

Oystercatchers nest in the open on rocky beaches just above high tide line and away from shoreline vegetation. They create nests by tossing pebbles, rock flakes and shell fragments with a sideward and backward flip of the bill, forming a small bowl-shaped depression. Males do most of the nest building, though females help too. Pairs, which are monogamous, may use the same nest bowl for several years in a row.

Human disturbance can cause oystercatchers to abandon a nest, so do not approach closely, and please do not bring your dog ashore.

Black oystercatchers are among a small number of shorebirds on the Alaska Watch List, a listing that aims to highlight declining and vulnerable bird populations before they become seriously threatened. Oystercatchers are being watched in Southeast Alaska because they are not very abundant, and they are considered vulnerable to continual human disturbance and habitat alteration.

Oystercatchers also are vulnerable to marine oil spills. During the Exxon Valdez oil spill 20 percent of the oystercatchers in the spill zone died, and breeding activity was disrupted by oiled shorelines and cleanup activities. No one knows if hydrocarbon concentrations in oiled mussel beds will have long-term effects on oystercatchers, but that is a concern because mussels make up 35 to 42 percent of the oystercatcher diet in Alaska.

Many oystercatchers live in Southeast Alaska year-round. Some migrate to British Columbia before returning to add one more colorful presence to our shoreline during spring and summer.

Marge Hermans and Bob Armstrong are authors of numerous magazine articles and nature guidebooks for Alaska. Contact Juneau Audubon Society at ckent@alaska.net. Monthly meetings resume in September.

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