Subject: Re: re quivering swallows
Date: Jun 2 21:05:15 1996
From: Don Baccus - donb at Rational.COM


>Adult Bald Eagles have contrasting body, head&tail colors. An eagle on the
>ground signifies "food" to other eagles.

So, an immy eagle on the ground signifies "no food"? If "food's here!"
were the selection factor driving the contrasting plummage I'd think
juvies would share it.

>Cliff Swallows are not nearly as contrasty in color. Wing quivering could have >evolved as an alternative strategy to attract attention (only when desirable).

They nest in areas where mud ain't all that available, and black mud and
water vs. pale dirt seems to be an obvious advertisment without the hassle
of burning energy in wing-flapping. When the mudhole is small, cliff
swallows will excavate it in large numbers (I've seen groupings of
dozens at once, from colonies numbering in the hundreds) and perhaps
the "keep clean" theory makes sense. As the excavate, the mud spot
becomes a quarry, deepening. The "lonely" barn swallow, being less
gregarious, and poaching mud more widely given their nesting needs,
perhaps don't make "micro-quarries" to the same extent.

Thus, the behavior may be an adaptation resulting from gregarious
behavior, rather than driving it.

>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).

Well, any male, perhaps, rather than her mate, given the intense rivalry
which appears to go on in these colonies.

- Don Baccus, Portland OR <donb at rational.com>
Nature photos, on-line guides, at http:://www.xxxpdx.com/~dhogaza