Martha’s Vineyard is a great place for birding, with a high diversity of birds present at most times of the year, and a remarkable record for producing outrageous rarities. But nobody has ever accused our Island of being good for gull-watching.
The problem, I’ve always opined, is our location, tucked into the armpit of Cape Cod’s arm. Gulls following the coastline end up on the outer Cape or Nantucket, with the land mass of upper Cape Cod intercepting southbound birds that might otherwise hit our shores. But for whatever reason, many of the gulls that are uncommon in our region approach real rarity on the Vineyard, and truly rare species virtually never show up at all.
Certain conditions, though, can change our luck, and among the most promising types of gull weather is a good northerly blow. While moving a lot of birds southward along the coast, strong north winds also heap up debris on the easily accessed (and birded) shorelines of Vineyard Haven, Oak Bluffs, and Edgartown. Two weeks ago, these conditions delivered the goods.
North winds and rain on Saturday, March 11, got things started, with the winds at least continuing their zeal into the next day. Vast quantities of slipper shells washed up on the Oak Bluffs waterfront, massed in rattling shoals at the high tide line. Many of those shells were empty, but enough were occupied to represent a huge bounty for scavengers.
As I traversed the waterfront on that Sunday afternoon, the usual modest local gull flock had grown perhaps threefold by birds attracted to the shellfish. I was out for a run, and hence had little time and only my uncorrected vision to examine them, but two birds quickly stood out. One was an immature Iceland gull, and the other an adult or near-adult lesser black-backed gull, both in a gull flock feeding on the shore across from Waban Park.
Routine as nearby as Nantucket, these two gulls are scarce on the Vineyard; a typical winter brings a smattering of reports, but neither species is a bird you can count on finding here on any particular day. So after my run, I returned to the site with my camera and binoculars. The lesser black-backed was gone, along with about half the more common species I had seen, but the Iceland gull was still present.
The next day, I tried again. While a lot of the slipper shells had either washed back out to sea or been covered by sand, gull numbers were still high. The lesser black-backed gull was still absent, and instead of the immature Iceland, I found a beautifully marked adult of the same species. Rob Culbert reported the lesser black-backed from Ocean Park a couple of days later, and I finally caught up with that bird, which proved to be in third-winter plumage, again across from Waban Park, on Friday, March 17.
An untidy taxonomic complex, Iceland gull as it’s presently constituted breeds at high latitudes from Greenland west to the Pacific Ocean. Eastern populations are very pale gulls, with adults lacking any black at all in their wingtips, and are notably delicate and round-headed in structure. More Western populations, including a form called Kumlien’s gull, which was once regarded as its own species, are more robust, show some black in the wingtips, and are the form we typically see. The most Western Iceland gulls, a form called Thayer’s gull that has variously been considered a separate species or a subspecies of herring gull, is the darkest of the bunch, with extensive black in the wingtips.
Any of these forms, though, appears more gracile, longer-winged, and almost always a bit smaller than the herring gull that is our region’s most common gull species. Like most large gulls, Icelands pass through a series of distinct plumages as they mature, achieving their ghostly adult plumage around their fourth year.
While it’s more straightforward taxonomically, the aptly named lesser black-backed gull presents an intriguing puzzle. Formerly, the mainly European bird was very rare in North America. Many 20th century field guides to our region didn’t even include it. But over the past 30 years or so, the species has increased dramatically in the Eastern U.S. Presumably it is expanding its breeding range westward, though the locations of any major North American breeding sites remain a mystery.
The species is an elegant one, with long wings, graceful and powerful flight, and, as its name suggests, dark back and wings. Like Iceland gull, the “LBBG” is a four-year gull, progressing from a mottled appearance during its first year to uniform dark-gray wings and back in adult plumage. The shade of gray varies somewhat, but always stands out amid a flock of herring and ring-billed gulls.
In the right place, seeing two Icelands and a lesser black-back would take just moments. But by Vineyard standards, three decent gulls in one week in one place constitutes an unusually good show, and highlights the ability of gulls to concentrate around a rich resource.