It's all about seeing and being seen.... Dennis and all you Tweeters, are
there any theories out there that the dipping behavior might enable birds to
see better what's beneath the reflective surface of a shimmering,
fast-flowing stream? Get a constantly changing series of different angles?

It would be interesting to consider, too, whether this behavior could
provide a kind of camouflage-by-motion, actually making it more difficult
for underwater creatures (whether potential predator or prey) to detect a
dipper when it dips.

Hal Opperman
halop at continuum.com
----------

Date: Thu, 31 Mar 1994 09:42:48 -0800
From: Dennis Paulson <dpaulson at ups.edu>

In answer to John Loegering's question, "why do dippers dip?"

My hypothesis is that many streamside birds have up-and-down
movements to communicate with conspecific individuals (mate, perhaps others
for territorial reasons). Streams are "busy," with a lot of horizontal
movement, and it would be easy to lose sight of a small bird working along
a stream. The vertical movement of a wagtail tail, a spotted sandpiper
rear, or a dipper's entire body, can be seen against that horizontally
moving background.

This is my own hypothesis and, as far as I know, hasn't been
published. There was a paper many years ago--I can't remember the reference
now--that tried to explain it as an intention movement to facilitate a
quick escape from an attacking predator. I can't buy that at all, but I
haven't seen anyone counter it in print.

Along with the dipping, of course, comes the rapid blinking of the
white eyelid, also conspicuous at a distance, and the two seem highly
correlated.

For the European Dipper, The Birds of the Western Palearctic
states: "In almost any situation, bird signals excitement, mild alarm,
threat, or mixture of these, by repeated Dipping and Blinking, rate of both
increasing when approaching nest, mate, or when disturbed by intruder."

If anyone has additional ideas or knowledge, I'd love to hear them.

I think I read that "ouzel" is supposed to be an American Indian
name, but I assume that this can't be, as there are European thrushes named
ouzels!

The Ring Ouzel is a large black thrush with a white ring around the
neck--certainly named before our dipper was discovered.

Dennis Paulson, U. of Puget Sound