[EBB Sightings] Unusual bird behavior

In Redwood on Friday, I was walking the lower stream
trail for photographs at the east end. 
I stopped by a stand of willows and other trees and
listened to mostly warblers. I could see them
back-lighted and thought I would go off-path into a
small clearing to get to good light. 
When I started out carefully picking a path through
some Forget-Me-Nots I scared up a Robin and a Spotted
Towhee who had been frozen and silent not two feet off
the path.  They flew up low into a tree in front of
me. I thought what an odd-couple, but carefully
checked for a nest anywhere not knowing if I was
somehow blundering around. 
I didn't see anything. The Robin squawked a bit and
flew off, but the ST kept chipping and chipping. Soon
it was joined by another smaller one ( mate?) low in
the same tree in front of me who joined in with the
chipping. I kept thinking "nest", but their attention
was not directed towards scaring me off. 
Then the strange things happened. Five warblers flew
in and began hopping from branch to branch in the same
tree. Then a Bewick's Wren flew in and hopped around
eye-level on another branch. Then, a Hermit Thrush
investigated...and then a Junco. The Towhees were the
only ones vocalizing. 
Finally after about five minutes, they all dispersed
and I ducked through branches to reach a small glade.
I found a place to stand and waited. No activity, so I
just waited and pished a bit. There was a little
interest from the warblers but nothing photogenic. So,
I continued standing there. 
I decided that if I moved a little to the right a
perfect branch with sunlight on it would be in view
and I could hope a warbler might use it. I looked at
my feet to try to make the adjustment without snapping
twigs, and wow! One foot away was a coiled Garter
Snake taking in some sun.
I then realized that I had probably scared the snake
into movement and caused the ruckus when I first
started out. I think the towhee and robin were keeping
an eye on it initially. 
And, after it settled down to sun, they did too. 
What was amazing was that what sounded like any other
towhee call seemed to be recognized as "SNAKE!" (or
predator) by so many other species...warblers,
Bewick's, Hermit, and Junco.
Has anyone else ever observed something like this?