On Sunday, a birding group from Mass Audubon Wellfleet Bay was sorting through migrant shorebirds on Morris Island in Chatham. The usual suspects were in place – Semipalmated Sandpipers newly arrived from Brazil; Dunlins, Sanderlings, and Ruddy Turnstones all in their breeding finery, plus shrieking Willets defending their nearby nests.
The numbers were modest, as is typical for spring – most shorebirds avoid this part of the world on their northbound journey. But among the dozens of expected birds was one that did not compute. It was the size and shape of a Dunlin, with that same long, down curved bill, but with red where the black belly should be. The leaders, David Clapp and Joel Wagner, quickly realized this was a rare visitor from “the Continent” – a Curlew Sandpiper.
Curlew Sandpipers breed in a relatively small area of Arctic Siberia, then make an impressive migration to Africa and Australia for the winter. This species used to be almost annual in spring on Cape Cod, but shows up much less often these days - it’s anyone’s guess why. And how does a bird that’s trying to get to Siberia from Africa end up on Cape Cod, anyway? That’s also up for debate, but the prevailing theory is that a few Curlew Sandpipers overshoot their fall migration to Africa, putting them over the tropical Atlantic and eventually in South America, where they settle in for the winter with other shorebirds. Come spring, these birds head north with the other North American shorebirds, ending up in places like Chatham. No one knows if and where these lost birds end up breeding, but it’s unlikely they find their way back to Eurasia from here.
This kind of vagrancy among long-distance migrants is often a dead end for the individuals – they won’t get to breed and pass on their genes, and that’s why this sort of vagrancy is rare. But this behavior also allows birds to colonize new areas if lightning strikes twice and they ever find a mate. Curlew Sandpipers have bred in Alaska as a result of overshooting their normal migration. And Clay-colored Sparrows and Blue Grosbeaks, both rare spring migrants in Massachusetts, have managed to find mates and breed on the Upper Cape in recent years. Obviously these colonizing birds can’t be picky about mates. It’s sort of a Steven Stills situation - love the one you’re with.
You may not find that next rare record that has the birders squealing their tires on their way to the mudflats, but nevertheless, now is the time to go look for spring migrant shorebirds in Massachusetts. We’re in the brief window when these Arctic bound birds are passing through while arrayed in their rarely seen breeding plumages. Since we mostly see shorebirds on their southbound migration, we don’t get to see their smart breeding attire, settling instead for their somber, gray winter tones. But in May, a Ruddy Turnstone is truly ruddy, normally flat-gray Sanderlings are a handsome rufous, and Black-bellied Plovers, have, well, a black belly. You’re still on your own with the peeps, the small, barely distinguishable shorebird species like Semipalmated and Least Sandpipers, as they are just as maddeningly, hair-pullingly difficult in spring. Take it from me - it’s how I got my current hairdo.