Voyage from Liverpool to Boston - Off South Coast of Irelnd.
1911.
August 2
(No 8)
[August 2, 1911]

Remarkable flight of Herring Gulls.
Set of their wings.

length of their gliding flights until the latter seemed, as I
have said, to be limited only by their wishes or mere caprices.
A corresponding progression and very noticeable if not also significant
change took place in the "set" of their wings. This is difficult to
describe but essentially it may be said to have consisted (1) in
the more general backward trend of the whole wing (2) in the
more decided crooking or bending of the wing at the carpal joint
(3) in the much more decided downward trend of the wing
quills and especially of the secondaries. The latter were so
deflected downward towards their tips at times as to give the wing
a curiously incurved or hollowed aspect anteriorly.
3. When the set wings, thus incurved, were struck by especially
firm gusts of wind one could see quite plainly and unmistakeably
that the tips of the secondaries were sprung or bent upwards by the wind
while the forward edge of the wing remained, of course, perfectly rigid.
It was primarily this observation which first suggested to my mind the
thought that the wind might seem thus to drive the bird against it.