Election Section

Long before Labor Day, the shorebirds began moving south. I’ve been seeing good numbers since early August: black-bellied plovers still in their dapper breeding plumage, least and western sandpipers working the tidelines, red knots, dowitchers, curlews. Among the migrant throngs, in singles and small clumps, are a couple of personal favorites, the small chunky sandpiper relatives called turnstones. 

There are two species, the wide-ranging ruddy turnstone and the strictly-east-Pacific black turnstone. These odd birds have been shunted back and forth between the sandpiper and plover families and even assigned a family of their own; current thinking places them among the sandpipers, close to the knots. Black turnstones are in fact mostly black with white streaking on the face, white bellies, and blackish legs; ruddies have black-and-white heads, red-brown wings, and orange legs. In flight, both turnstones have a striking black-and-white pattern, with white back, wingstripes, and tail.  

The name is descriptive. Both turnstone species forage by looking under things—stones, shells, seaweed, all kinds of beachwrack and jetsam—and flipping them over with their short, slightly upturned bills. (Turnstones are not quite as anatomically specialized as another shorebird, the wrybill, a plover whose beak curves to the right. If I ever get to New Zealand, I intend to look up the wrybill.) Under the stones or whatever are tiny crustaceans called amphipods and isopods, worms, and snails. At Bodega Bay, black turnstones have been observed flipping over the edge of algal mats and using their bills and heads to push the algae away in a snowplowing motion. They like clams, too, and follow clam diggers across the mudflats, scavenging their leftovers. 

But turnstones have more than one card to play. Both species are pretty opportunistic in their foraging methods and adventurous in their tastes. At some seasons, the diet of black turnstones consists largely of herring roe. They use those stout bills to hammer open barnacles and mussels and pry limpets off rocks. They’ll also head-butt clumps of seaweed to flush out kelp flies and other arthropods. Bradford Torrey described this technique in 1913: “…they drew back a little and made a run at [the seaweed] as men do in using a battering ram.” In southwestern Alaska, they follow streams inland to feed on the carcasses of spawned-out salmon. 

Ruddy turnstones have an even more diverse diet, with seasonal variations. During their breeding season in the far north, they switch from seafood to vegetarian fare, mainly the seeds of rushes and sedges; later, to insects and spiders. Ruddies don’t mind carrion, either, or the meat scraps they find around human homes and hunting camps. The population that migrates up the Atlantic coast in the spring gorges on horseshoe crab eggs at Delaware Bay, a key shorebird stopover threatened by overexploitation of the adult crabs for fishbait, fertilizer, and medical uses.  

What ruddy turnstones are most notorious for, though, is egg predation. When their migrations coincide with the breeding seasons of other seabirds, they can wreak havoc in nesting colonies. Almost 80 years ago, ornithologist Alexander Wetmore watched turnstones attacking the eggs of sooty and gray-backed terns on remote Laysan Island. As his party of scientists and sailors walked through the tern colony the turnstones followed, going after the nests when the terns rose to protest the intrusion: “The turnstones ran quickly about driving their bills into the eggs without the slightest hesitation, breaking open the side widely and feeding eagerly on the contents, sometimes two or three gathering for an instant to demolish one egg and then with this one half-consumed running on to attack another.” 

In 1977, Robert Loftin and Steve Sutton watched a gang of ruddy turnstones wipe out a royal tern colony in Florida’s Nassau Sound. 

Although they would defend their nests against larger predators like gulls, the terns seemed nonplussed by the turnstone assault. They eventually abandoned the colony. Other reports of nest depredation come from colonies of sooty terns in the Dry Tortugas, common terns off Long Island and near Toronto, and multiple seabird species in Finland. 

Black turnstones have been caught in the act too, but only on their Alaskan breeding grounds. Pairs of turnstones drive incubating phalaropes and longspurs off their nests, then puncture the eggs. But the black turnstone’s oddest dietary quirk has been documented here in California where many winter. Burney Le Boeuf of UC Santa Cruz, who has studied the northern elephant seal colony at Año Nuevo for years, has seen the birds picking at open cuts and sores on the seals’ bodies, feeding on their blood. 

Vampire birds? As odd as that seems, the blood-drinking habit has evolved several times among birds. The closest parallel is a small songbird called the tussockbird that feeds on the blood of southern elephant seals in the Falkland Islands. The red-billed and yellow-billed oxpeckers of Africa, aberrant starlings that usually pluck ticks from the bodies of large mammals, sometimes eliminate the middleman. And on Wolf and Darwin Islands in the Galapagos, the sharp-beaked ground finch uses its sharp beak to peck the wings and tails of the large and notoriously dim seabirds called boobies, and drinks the blood that flows from the wounds. 

The natural world is full of extreme specialists—insects that feed on the nectar of a single species of flower, parasites that live not only on a single host species, but a specific body part of that species. In his ever-timely essay entitled “Nothing in biology makes sense except in the light of evolution,” Theodosius Dobzhansky mentioned a fungus that grows only on the rear portion of the wing covers of one species of beetle, itself confined to a couple of caves in the south of France. But resources are always unpredictable, and in the long run it often pays to be a generalist. Creatures like the black and ruddy turnstones, willing to eat anything from seal blood to garbage, may be around long after more specialized species have died out.›