While looking for burrowing owls down at the Berkeley Marina a few weeks ago, I was surprised to run into a pair of black oystercatchers working the riprap along Cesar Chavez Park. Maybe I shouldn’t have been. I’ve always associated these birds with the wave-bashed rocks of the outer coast, but I’ve since read that in Washington State, at least, oystercatchers are beginning to colonize more sheltered shores. Maybe that’s happening in San Francisco Bay as well.
Anyway, they were hard to miss: stocky duck-sized shorebirds with brownish-black plumage, chisel-tipped vermillion beaks, sturdy dull-pink legs, and baleful yellow eyes. I last saw them flying north together, calling to each other. I’m assuming a pair because oystercatchers, unlike some shorebirds—the promiscuous ruff and the polyandrous phalaropes, for instance—mate for life. And that can be a long haul; banded oystercatchers have lived for 16 years in the wild. At least life partnership is the norm, although divorces have been recorded.
If you spend much time around oystercatchers, you’ll eventually see what ornithologists call the Piping Display. They seem to break into it at moments of high emotion: courting a mate, maintaining a pair bond, defending a boundary. Hunching over with bill downward, they give a series of pennywhistle notes while repeatedly bowing. Sometimes they rotate in tight circles, still piping.
About that name: yes, I know it’s less than appropriate. As the 19th century ornithologist Elliott Coues said, “Oysters do not run fast.” Some have tried to salvage it by saying the birds “catch” oysters unaware, but I wouldn’t want to assume that much about an oyster’s level of awareness.
Black oystercatchers, which inhabit the Pacific Coast from Alaska to Baja California, don’t seem to care much for oysters even when they’re available. They’d much rather eat mussels. (The bird’s Atlantic counterpart, the black-and-white American oystercatcher, has in fact been observed feeding in oyster beds.) Less favored items include limpets, whelks, sea urchins, marine worms, and crabs.
We tend to reserve the concept of predator for creatures that chase their victims down in dramatic fashion, or lunge at them from ambush—not one whose prey is rooted to a rock. But the oystercatcher is as predatory as the wolf or the weasel, in its own way. And it has a technique for each kind of prey. Oystercatchers forage for mussels in the intertidal zone, watching for those whose shells are gaping the way they should be after being steamed with white wine, butter, and celery (if you follow the Belgian tradition). They insert those long bills into the gap and snip the adductor, the mussel’s muscle that closes the shell. Then they remove and gulp down the contents.
Limpets are dislodged from the rocks where they’re attached with a quick jab of the beak at the point where the shell meets the rock, flipped over, wedged into a crevice, and eaten. The birds punch holes in sea urchin shells to get at the bits that are served in sushi bars. On occasion they probe for bivalves buried in sand or mud.
The requisite skill doesn’t come naturally. Young oystercatchers have to learn their trade. Newly independent chicks make do with limpets and worms until they’ve mastered their mussel-opening technique, and it can take them over 3 years to learn how to deal with a sea urchin.
It’s even more complicated for young Eurasian oystercatchers (there are 10 species scattered around the world’s coasts, 11 if the Canarian black oystercatcher is still with us). The Eurasian birds are specialists, either stabbers or hammerers. Stabbers use the jab-and-snip approach of the black oystercatcher; hammerers pry a bivalve loose from its moorings, then break one of its shells with a volley of short, sharp blows. The commitment to one craft or another, which fledglings pick up from their parents, will affect the shape of the bird’s beak: hammerers have blunt-tipped bills, stabbers pointed.
There may also be a gender component to feeding strategy. Among black oystercatchers, at least, females are larger than males and have longer bills. Bill-length dimorphism in shorebirds often signals dietary differences; it’s not clear whether this holds true for the oystercatchers, though. There’s a dissertation topic for somebody.
Back to the burrowing owls: looks like I was in error about the burrowing owl in the BART station. Although it was reported as such in North American Birds, the New York Times-cum-Sporting News of birding, I have it on good authority that the bird in question was actually a saw-whet owl. Thanks to Andrew Smith for correcting the record.ã