The day before yesterday I wrote:

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

Don replied:

>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.

Sorry for the delayed reply, I'm on digest mode.

First of all I should have said that an "adult" eagle on the ground "often"
signifies food. After all, eagles taking a bath for instance, are also at
ground level. But to get back to the point I was trying to make; It is my
understanding that immature plumage possibly evolved to signify lack of
experience in a younger bird. Whether as a sexual partner, food provider or
any other number of activities eagles gain experience in. I've seen immature
Bald Eagles on the ground a lot, especially in the first months after
fledging, and if their presence in that location were to attract other eagles
looking for food, those other eagles would waste a lot of time.

I don't think that an immature eagle on the ground signifies "no food" per se,

but that it sends a different message to other eagles than an adult on the
ground.

About the quivering Cliff Swallows Don wrote:

>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.

My experience with mud-gathering Cliff Swallows is limited to Umtanum Canyon
(eastern Washington) where, like Don describes, out of colonies of hundreds,
dozens of swallows gather along the bank of the river. The "mud hole" is not
an obvious darker hole contrasting with paler soil around it. Perhaps my
observations in this single locality influence my interpretation too much.

Tonight I did what I should have done last night. I pulled out the slides I
have of these mud-gathering Cliff Swallows and the ones I have of
mud-gathering Barn Swallows.

A few thoughts based on closer study of the slides:
Many Cliff Swallows, while bending down for mud also cock their tails way up.
Especially this last point makes me re-think my initial remarks about lack of
contrast in plumage in Cliff Swallows. I assume that the rump patch
(contrasting color) serves a purpose. Does the tail movement show & hide the
rump patch? Or is it indeed simply a ways to keep it clean? But see below. One

slide shows a Cliff Swallow taking off with its tail touching the mud.

If the wing quivering has a function in keeping feathers clean, then why
doesn't the barn swallow with much longer tail feathers exhibit this same
behavior (same point Jerry Blinn made in his original posting)?

Perhaps the placement/anatomy of the legs & feet and the total length of the
legs and possibly distribution of weight is different enough in the two
species. According to Godfrey in The Birds of Canada, tarsus length for (adult

male) Cliff Swallows is 12-13 mm with a 12.3 mm average. For (adult male) Barn

Swallows 10.5-11.5 mm with an 11.3 average. That doesn't strike me as a
significant difference in tarsus length. Turner & Rose in Swallows and Martins

an identification handbook give similar tarsus measurements. In addition they
give weights. A mean of 21.6 grams for Cliff Swallows. A mean of 18.9 grams
for Barn Swallows. Perhaps the heavier weight of the Cliff Swallow makes them
more prone to sinking into the mud after all.
One interesting note is that Turner & Rose describe the mud-gathering behavior

of the Cliff Swallow as a social activity, during which males attempt to
forcibly mate with females. Do you suppose the wing quivering is a way to ward

off forced copulation? But then one would have to assume that most, if not all

birds seen gathering mud are females, for almost all birds gathering mud
quiver their wings (at least in my experience and slides). Although the male
starts the nest construction, both male and female finish it (Turner & Rose).
Interestingly the bibliography in Turner & Rose gives the following entry:
Butler, R. W. (1982b) Wing-fluttering by mud-gathering Cliff Swallows:
avoidance of 'rape' attempts? Auk 99: 758-61.

Does anyone on tweeters have this Auk on his or her shelves? If not, I'll
visit the library soon to see what exactly Butler wrote.

Fascinating stuff, this.

Martin Muller, Seattle
martinmuller at msn.com