You’d think the colonization of the Vineyard by a large, noisy bird species would be an obvious process. But the gradual establishment of a second species of crow on the Island — the fish crow, Corvus ossifragus — has been masked by the resemblance of this species to the American crow, which has been here all along. Unless you pay close attention, you might easily be unaware of the change.
Fish crows were rare here as recently as a decade ago, but their wintertime numbers have steadily grown. The change is most evident along the shoreline from Vineyard Haven center around East Chop to downtown Oak Bluffs, where a flock of fish crows present in recent winters has multiplied dramatically in size this season. The birds move constantly, and the flock often divides, so it’s hard to pin a number on the phenomenon: My guess would be that from 200 to 400 fish crows are active in this area on a typical day. The birds are talkative and sociable, often traveling in a raucous, untidy flock.
I haven’t been birding up-Island for many weeks now, and so I have no sense of the fish crow’s current status farther west. It’s certainly a species to look for along the Vineyard Sound shoreline, around Lake Tashmoo, and in Menemsha, where human food sources augment natural ones in a way that crows find attractive.
Our two crow species are virtually identical in plumage and uniformly black; they overlap in most body measurements. But the fish crow averages smaller, shorter-legged, and significantly thinner-billed than the American crow, and more subtly, its wingtips appear slightly more pointed. The easiest way to distinguish the two species is by their calls: American crows give the quintessentially crow-like “Caw!” note, while the fish crow’s call is softer and more nasal — something like “cwuck” or “cuh-uk.” Happily, both species of crow are talkative, and it’s usually apparent whether you’re viewing a flock of fish crows, American crows, or a mix.
The habits of these two species are quite similar, though as its common name suggests, the fish crow associates more closely with water than the American crow does. (Its scientific species name, “ossifragus,” means something like “bone-crusher,” and probably originates with the fish crow’s habit of scavenging carrion along shorelines.) The Vineyard Haven fish crows frequently feed along the wrack line, and they pick over shells that gulls have fed on. (American crows use these food sources, too, but much less regularly than the smaller species does.) Both crows are opportunistic feeders, and will eat anything edible they can find, from seeds to insects to dumpster contents. During the summer, both species are notorious for preying on the eggs and nestlings of other birds — a natural behavior, but one that can offend human sensibilities or even represent a conservation concern, if their prey includes threatened birds like piping plovers.
Fish crows tend to be more gregarious than American crows, rarely turning up as isolated individuals. The two species flock together routinely, though, and while they don’t seem to interbreed with much regularity (or the species would no longer be distinct), crows often don’t pay much attention to the difference.
Formerly a bird of the Mississippi-Ohio river drainage and the coast of the southeastern U.S., fish crows expanded their range considerably during the second half of the 20th century. Once a rare bird in Massachusetts, they were regularly breeding in limited areas near Boston and in the Connecticut River Valley by the time I began birding seriously around 1970; within a couple of decades they had expanded onto Cape Cod, and so their arrival in numbers on the Vineyard was probably inevitable.
Oddly, though, fish crows have yet to be documented breeding on the Vineyard, despite the fact that American crows are common nesters on the Island. But for decades now, American crows from the mainland have migrated to the Vineyard for the winter, joining our breeding crows in forming nocturnal roosts that sometimes number in the thousands of birds. Many of these crows can be seen flying to the mainland to forage during the day, or flying back in the evening toward their Island roosts. Apparently fish crows, as they grew more common on Cape Cod, simply adopted the migratory pattern of American crows and blended into the winter roosts on the Island.
Currently, the commuting crows seem to consist of a combination of the two species, but many fish crows have evidently simplified their lives by skipping the commute and spending their winter days here, as well. It would be surprising if this pattern of winter occupancy didn’t turn into breeding some year in the very near future, and indeed, fish crows may well be nesting here undetected already.
Often regarded as unappealing birds, crows are, in my opinion, underrated. They’re highly intelligent birds with elaborate social structures and very flexible behavior. The addition of a second species to the Island’s avian fauna strikes me as an interesting development, and I’m following this ongoing process with considerable interest.