Wild Side : Identifying gulls can make even expert birders wince
Photo by Matt Pelikan
If you pay attention to nature, you've probably heard of this winter's incursion of snowy owls into the United States: the unusually large southward push of this predator has been covered by the national media as well as by this column (December 22, 2011). Equally interesting to Vineyard birders has been a spate of recent sightings of two other white ghosts from the far north: Iceland and glaucous gulls. Neither is ever common here, though they occur more or less annually. But given recent reports and the point in the season, the next week or so offer an unusually good chance to spot one.
While they are distinct species, these two are so similar in appearance and habits that it makes sense to discuss them together. In size and shape, they resemble our most common gull, the herring gull: Icelands average a bit smaller than a herring gull, and glaucous gulls are generally larger. But in every plumage from youth to adulthood, these northern gulls are markedly paler than herring gulls (or indeed any other of our regularly occurring gull species).
In birder shorthand, the two species are collectively known as "white-winged gulls." First-winter birds range from nearly white, usually with flecks of darker pigmentation, to the color of heavily creamed coffee (a herring gull of that age is an honest brown). By adulthood, the wings and back of a glaucous or Iceland gull are pale gray, much lighter than the similar parts of a herring gull. (Note, though, the angle at which light hits a gull's feathers can make it hard to judge color accurately.) Perhaps most usefully, the northern species have little or no dark pigmentation in their wingtips, where adult herring gulls have pronounced black patches with white "windows."
The Iceland gull, breeding mainly in southern Greenland and subarctic eastern Canada, is a variable species. In the Greenland portion of its range, an adult's wingtips are pure white, while as you move farther west, the wingtips average progressively more gray. Biologists are uncertain where to draw the western limit for this species, which somewhere along the way morphs into the very closely related Thayer's gull. Such genetic untidiness is the rule rather than the exception for gulls, to the dismay of birders hoping for simple identification chores!
A truly circumpolar bird, glaucous gulls are believed to be uniform across their range. This species, nesting even father north than its smaller cousin, can generally be recognized by its heavier build, flatter head shape, and, especially, longer and more robust bill. Also, all or nearly all of our adult Iceland gulls (which originate from the Canadian population) show at least a little dark in their wingtips, which are invariably pure white in glaucous gulls.
Look for either of these species any place gulls congregate, which generally means either a pile of debris or a shoreline where a strong wind is washing up weed and uprooted shellfish. One glaucous gull has been seen repeatedly on a pile of scallop shells along Lagoon Pond Road in Vineyard Haven. Sightings of this species have also come from along the Beach Road and the South Shore. An Iceland gull has been seen several times along the Oak Bluffs waterfront: your best odds of finding it here come when the wind has made it east of north, driving masses of weed up onto the beach below the sea wall. The distinctive coloration makes either species stand out among our more common herring, ring-billed, and great black-backed gulls.
What I love most about these birds, though, is not their ethereal plumage but their wildness. Visitors from remote, desolate shores, the ones we see here have traveled hundreds or thousands of miles, meandering southward in search of food. In flight, they show an efficiency suitable to their long-distance wanderings: their wings are stiffer, more blade-like, than those of a herring gull, and the wingbeat, which is shallow and comes mainly from the shoulder, suggests ample power in reserve. These birds are comfortable flying in winds that ground a herring gull, and Iceland and glaucous gulls often patrol a long stretch of coastline rather than landing and feeding in one small area. They can be pugnacious, too: though smaller than a herring gull, an Iceland gulls acts like it is larger, often bullying food away from its more common relative.
By the end of March, these birds and any of their colleagues that have made it to the south of us will likely have headed back north, and these species will be gone from the Vineyard until early next winter. They will spend the intervening months taking advantage of the long days of high-latitude summer, mating and raising their young. A dream of mine is to travel north to watch them on the barren shorelines of their homeland.