Wild Side: Nature riffs like a jazz musician

The overwintering “goldeneye” ducks may look alike, but they are different birds.

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I’ve always had a fondness for the little clusters of closely related species that evolution can produce. Sometimes it’s a whole genus, like those infuriatingly similar Empidonax flycatchers; sometimes it’s just a species pair, like the two goldeneye ducks that winter annually in Vineyard waters. In any case, these instances seem like nature feeling smug for having a good idea and then riffing on that notion like a jazz musician.

Those goldeneyes, for instance, share an overall appearance, and many of the basics of their life histories (nesting in tree cavities, for example). But seen well, they are unmistakably different birds. Both species occur around the Vineyard in winter, but these closely related ducks differ dramatically in their distribution and abundance.

The more numerous of the two, the common goldeneye, nests clear across Canada, and in portions of the northernmost U.S. In winter, this hardy duck inhabits oceanic coastlines throughout the East and West Coasts, extending northward to Newfoundland in the East and the Aleutian Islands in the West. The breeding and wintering ranges in the Old World are similarly extensive; this is one common and widespread duck, with the North American population alone estimated at about 1 million by researchers.

While the species may be most prevalent in winter on coastal waters, wintering birds can be found on rivers, lakes, and ponds across the lower 48 states, and the breeding habits of this bird focus resolutely on freshwater habitats.

The distribution of Barrow’s goldeneye, in contrast, is much more restricted. This bird is almost entirely a North American species (a small population breeds in southern Greenland, and Iceland hosts some wintering birds). But the range is broken into two widely separated populations that appear to have little if any contact with each other.

The bulk of the species nests in the Pacific Northwest, west of the Rockies, and ranging from Washington State to southern Alaska. The province of British Columbia hosts the vast majority of breeders, and estimates of this western population range as high as a quarter-million individuals. The disjunct eastern population, in contrast, numbers only about 4,000, and packs into a small nesting area on the northern side of the St. Lawrence River estuary. It is from this tiny population that our wintering birds originate. Unlike its sibling species, Barrow’s goldeneye is strongly coastal in winter, and we are near the southern limit of its usual wintering range.

Given the difference in status between these two species, it is no surprise that the common goldeneye is a routine part of our winter avifauna, while Barrow’s goldeneye is rare enough so that birders will happily make a special trip to see this species when it turns up.

Numbers from the Vineyard Christmas Bird Count (CBC) illustrate the difference in local abundance. Common goldeneye numbers peaked in 1986 at 2,479. While numbers appear to have declined steadily since then, echoing an apparent but unexplained rangewide decrease, this species still remains a common one around the Vineyard in winter. Barrow’s goldeneye, on the other hand, is missed on more CBCs than it is found, and numbers in years when the species does occur, it’s invariably in the low single digits. (The highest count, in 1994, was four). It’s fair to say that, on average, less than 1 percent of the goldeneyes wintering around the Vineyard are Barrow’s goldeneyes.

Seeing a Barrow’s goldeneye in winter is facilitated a bit by one convenient habitat: Individual Barrow’s goldeneyes tend to return to the same location year after year, lingering there for much of the winter. In recent years, a fine-looking drake has hung out with a small group of common goldeneyes in outer Vineyard Haven Harbor, near the drawbridge. (This winter’s first report, by Rob Culbert on Jan. 9, was right on schedule.) In years past, a female was consistently present along the shoreline of West Chop, and prior to that, back around the turn of the century, a different female was a regular for several years below the bluffs of East Chop.

While similar in overall appearance, these two close relatives are easy to distinguish in the field. Barrow’s features a steep forehead, versus the more gradual slope seen on common. Drake Barrow’s goldeneyes show more black on the back than their cousins, and a prominent white spot on the face is round on common, but clearly comma-shaped on Barrow’s. At close range and in good light (don’t count on this!), Barrow’s drakes have a purplish gloss on their heads, while common goldeneyes show green iridescence. On females, aside from head shape, bill color is most helpful: Nearly all yellow in Barrow’s, mostly black on common.

Late migrants in fall and early migrants in spring, goldeneyes are with us from roughly mid-November into late March or early April. Look for them in shallow, sheltered waters, including bays and brackish ponds, where they feed by diving on a range of mollusks and other bottom-dwelling invertebrates. But act soon: The winter is passing quickly.