Wild Side : Migrating brant spend the winter in Ocean Park
File photo by Tim Johnson
All winter long, Ocean Park in Oak Bluffs hosts an odd juxtaposition of two vastly different populations of geese. The larger birds, sporting the familiar white cheek patch, pale breast, and white rump, are Canada geese, members of the Island's feral, non-migratory population of this species. Familiar to the point of annoyance, these Canada geese barely qualify as wild birds.
Their smaller companions, darker and marked with a white "necklace" across black neck, though, are at the other end of the spectrum. These are brant, wary winter visitors from distant breeding grounds. And while their apparent comfort in the midtown setting of Ocean Park may suggest otherwise, these are among the wildest birds you could name.
The habit of grazing on lawn grass is a relatively recent innovation for brant, and indeed this may be a behavior that's distinctive of our wintering population in particular. Because this small goose was a favorite target of gunners in the 19th and early 20th centuries, we have relatively complete records of the history of brant in the Bay State, and it's interesting to see how our birds fit the overall picture.
Transient brant, that is, birds passing through the Vineyard on their journey north or south, are rarely reported. Once or twice, I've seen small southbound flocks pass Gay Head in the fall. But the presence of a good-sized group, ranging from about 40 to as many as 150 some years, has been an Oak Bluffs specialty for as long as anyone remembers.
The presence of wintering brant on Martha's Vineyard was noted, for instance, in a 1925 species account by Arthur Cleveland Bent. At that time, the Island represented an extreme northern outpost for brant in the winter, with most of the population wintering on the mid-Atlantic coast. Since then, probably reflecting global warming, the winter distribution of brant has shifted northward, with large flocks now occurring north to Boston Harbor and the Massachusetts north shore.
While I have no actual proof, I suspect that the Vineyard brant represent a relatively stable sub-population, the same birds and their descendants returning to winter in a traditional spot year after year. (Color-banding a few individuals and waiting to see if they show up the next year would confirm or deny this assumption.) The fairly stable flock size, the consistent arrival time (around the first of November) and departure date (early May), plus the fact that these birds arrive already displaying their unusual penchant for grazing on lawn grass, all argue for continuity. But over the years, things have changed dramatically for these birds.
Most notably, since Bent's account was written, the coverage of eelgrass has declined dramatically, victim of declining water quality and a mysterious blight that struck in the 1930s. Originally, eelgrass was the staple food of brant in the winter, and the birds spent hours around each low tide feeding on exposed eelgrass. Today, relatively little eelgrass persists around the Vineyard in water shallow enough to allow the brant to feed; in a tribute to the flexibility of these wily little geese, our flock simply switched its diet over to a different kind of grass.
Brant nest in a ring of desolate tundra all around the arctic circle; few nest any farther south than the 70th parallel. The North American population concentrates in north-central Canada, north of Hudson Bay. While the migration route of these birds takes them overland across portions of Quebec and the Maritime Provinces, these flights are usually rapid and nonstop; overall, migrating and wintering brant are largely coastal in their behavior. Even locally, when some of the Oak Bluffs flock occasionally flies to Vineyard Haven or West Chop to feed, they invariably follow the shoreline rather than cutting across the land.
Departing on a south wind in early May, our birds probably fly swiftly to staging areas in Nova Scotia, with, perhaps a stop or two in Cape Cod or Maine waters. With a still-air speed of about 35 miles per hour and the benefit of a stiff tailwind, that leg of their migration may only take these birds a day or two. From there, they will await ice-out in the far north, finally nesting and laying their eggs in mid or late June. Beginning in late September, the reverse journey follows a similar pattern of several long, nonstop legs; while a vanguard of a few individuals may arrive first, the full number of the winter flock usually arrives in a very short window, echoing their equally sudden disappearance in spring.
Chunky and powerful despite their modest size, the brant is a species highly evolved for long journeys and the exploitation of a brief but fertile season at high latitudes. It's an amusing contrast to see these quintessentially wild birds mixing in with the semi-tame, resident Canada geese on Ocean Park. But it's a also a reminder of the resourcefulness of wild animals, and the ways in which our little Island is connected, through the journeys of wildlife, with distant and utterly different parts of the world.