Jerry and fellow Tweetsters,

On June 1, Jerry Blinn wrote about the difference in behavior between Barn and
Cliff Swallows while gathering mud; the wing quivering behavior by the Cliffs.
I don't have any specific information, but would like to add the following
thought.
Jerry already mentioned the difference between gregarious Cliff Swallows
(colony nesters) and loner Barn Swallows.
Could the wing quivering behavior have evolved as a signal to other Cliff
Swallows? I.e. "over here for good mud!"
Adult Bald Eagles have contrasting body, head&tail colors. An eagle on the
ground signifies "food" to other eagles. Cliff Swallows are not nearly as
contrasty in color. Wing quivering could have evolved as an alternative
strategy to attract attention (only when desirable).
Note also that in Bent Coues is quoted describing how the (probable) female
waits for the mate at the nest under construction, ecstatically quivering her
wings upon his approach (with redoubled cries of joy no less). I have never
seen this particular part of the nest building behavior, but if it is correct,
I feel it adds to the theory of the quivering having a signal function (i.e.,
"over here with that mud!").

Martin Muller, Seattle
martinmuller at msn.com