Joe Wetmore and I just returned from several days in the Provincetown, MA
area. On Monday, while we were hiking to High Head Beach (North Truro)
along the Cape Cod National Seashore, we witnessed what seems to be a
fairly lightly documented phenomenon in that area: the massing of American
tree swallows on their migration south. While the locals we later talked to
mentioned that they frequently see a lot of tree swallows along the Cape in
the fall, what we serendipitously encountered was really intriguing.

On our walk, as we crested the dunes and could see the ocean, we noticed
large clouds of birds swirling overhead. The white bellies, calls, and
flight patterns were a fast clue that these were tree swallows, these birds
were surprisingly round. Well, fat. The birds all landed on the beach in a
group, not far from the surf line, each one perched on the highest ridge of
sand in the vicinity. The flock numbered about 3000. All sitting on the
sand, facing south. Occasionally, they would startle, and most take to the
air, only to settle down again.

A naturalist on our whale watching trip later the next day congratulated us
for seeing these birds, since he knew of few birders in the area who talk
about these migration massings. When I checked eBird later that night, the
records there resonated...sitings of 80, maybe a few hundred there. Ebird
kicked my report back, in fact, asking me whether I'd actually seen 3000.
The whale guide indicated that a little bit south in Wellflleet, he sees an
estimated 100,000 there some years.

After doing a little reading, it made sense. The swallows are gorging
themselves silly on the lipid-rich bayberries that grow along the dunes,
fattening up to fuel their long flights to southern wintering grounds.
Bayberries are their second preferred food after insects. The following day
at Race Point, we saw more flocks along the coast, looking from a distance
like black haze moving along the shoreline, then coming in waves to the
shrublands in back of the dunes, presumably to eat more.

While this was just dumb luck to have seen what we did, I bet it would make
a great research project for some enterprising student. I just count myself
as fortunate, particularly when I thought the swallows living around the
Finger Lakes had been gone for over a month already.

Karen Edelstein


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