By the numberless thousands they descend. The birds arrive as a great host, flying from the northeast, following a sinuous path on invisible, atmospheric currents. The flock appears as a river of birds, curving through the air, with birds pouring forth in a flow that seems unceasing.

The great flocks of migrating tree swallows have arrived upon the plains of Quansoo and elsewhere on the shores of Martha’s Vineyard. By sunset at the end of a gray Labor Day, some hundreds of members of a flock of swallows had alighted on the branches of a black cherry tree and on the upper boughs of a neighboring eastern red cedar.

The swallows appeared restless. The birds would roost in the branches, all of them facing south, seemingly situated for the night. Yet after a moment or two, the birds would take flight en masse, wheel about in a choreographed spin, and then alight again. On the cherries, the swallows appeared to favor branches that terminated in dead, leafless twigs over those branches that bore leaves to the distal ends.

From a distance, the flocks of swallows appeared very much like swarms of bees. Tumbling, wheeling, circling, the swarms of swallows soared over the plains. Some pairs of swallows, separated from the flocks, dashed over the meadows, flying low, and skirting the tassels of switch grass as they snatched insects in flight. A few individual birds hovered in the air above, one perhaps 50 feet high, another 100 feet high, perhaps acting as sentinels for the rest of the flock.

Of the plants, the bayberry attracts the swallows. Along the margins of Black Point Pond, the bayberry shrubs now bear their waxy gray fruit in profusion. These bayberries can be gathered up, and when boiled in a large pot, the wax will separate from the fruit. The wax can then be skimmed off, allowed to cool, and used to make a bayberry candle. As someone who has attempted this, I can attest that one will have a very dark winter should one choose to rely on bayberry candles as a source of light. Fortunately for the swallows, they rely on bayberries not for illumination, but rather for sustenance. They find the bayberries a plentiful and valuable food source. The swallows stop at Quansoo or Katama or on the headlands of Cedar Tree Neck. On the bayberries they feast, before rising in a cyclonic swarm to cross the ocean on the next stretch of their migration.

These great hosts of swallows are, after all, migrating. What we witness here in September is a great wonder of nature, a scene of throngs of animals engaged in an annual migration. The flights of swallows do not equal the long lost flights of the passenger pigeon, so numerous that the flying birds darkened the sky and the roosting birds snapped limbs from trees, but the swallows do call such a migration to mind. The swarming swallows, the nonresident Canada geese flying in V-formation, the striped bass following cold waters back to Island beaches, the plovers scurrying from waves that lap the opening of the Tisbury Great Pond — all of these migrants pass the Island as summer turns to fall.

We recognize this change of the seasons. We, too, migrate, and change along with the changes in the light and the weather. The sassafras turns a speckled orange, and passengers by the thousands walk the gangways in Vineyard Haven and in Oak Bluffs and board the ferries, bound for the mainland. The sumac turns a bright red, and the school bus pulls up by the mailboxes. The seasons are changing and, sometimes, we take a moment to mark the changes in our own lives.

On the plains, the raindrops of a cloudy afternoon still cling to blades of grass. The little bluestem has turned a ruddy purple. Hazelnut bursts with fruit, its brown-tinged clusters of nuts splitting open. Goldenrod droops its yellow blossoms over the edges of the dirt road. The surf sounds in the distance, and above, and all around, a thousand tree swallows fly and dart and swarm and roost. The swallows are bound for a distant land, but for one September night, here they sleep.

Adam Moore is executive director of the Sheriff’s Meadow Foundation. This piece was published on the Sheriff’s Meadow website and is reprinted with permission.