I'm afraid this may be a bit of a damper on the interesting discussion that
John Loegering has started about why Dippers dip, but it's an important
damper. The question raises some important issues about adaptation and
about giving rational explanations. As long as people have
thought rationally about evolution in a Darwinian sense, with natural
selection as a key agent, it has been natural to think that an organism's
features are designed by evolution to optimize the organism's
ability to do something--often, to solve some problem of life, such
as getting enough food or finding a mate. In general, optimization
theory is quite rational, but it has an important pitfall: that we may
be telling a good yarn rather than providing an explanation. In Krebs
and Davies's wonderful book _An Introduction to Behavioural Ecology_
(Blackwells, 2nd edition, 1987), they say (p. 73), "One temptation when
presenting functional explanations in biology is to invent clever stories
which are difficult to test. For example we might suggest that
flamingoes are pink so as to blend in with the setting sun, so that lions
find them difficult to see in the evening when out hunting. You may
think this is an unlikely idea! But for all we know, the proposal that
brown moths are so coloured to blend in with the tree trunks on which
they rest may be equally unlikely. We need to perform experiments to test
our functional hypotheses."

The temptation is always to assume that every feature of an organism is
in some way adaptive and that we should be able to explain it
functionally. But our view of adaptation was changed forever (or should
have been changed) by a classic paper by Gould and Lewontin, "The
spandrels of San Marco and the Panglossian paradigm: a critique of the
adaptationist programme," (most easily found in "Conceptual Issues in
Biology," edited by Elliott Sober [MIT Press, Cambridge, 1984]). Even
though we always try to find functional explanations--and _should_ try,
clearly--we must accept that many features of organisms may be quite
accidental and have no functional value at all. (Flamingoes get their
pink pigment from the shrimp they eat; presumably white flamingoes eating
different food would be just as well adapted as pink ones are.)

Why do Dippers dip? Dennis Paulson's explanation is quite rational; it
stems from comparative observations, noting a behavior common to birds
that feed alongside streams. Maybe it's right. But how can we test it?
An explanation that can't be tested remains a plausible, perhaps
fascinating, story, but it isn't quite a scientific hypothesis unless
there's a way to falsify it. And John Loegering isn't going to get a
thesis out of the Dipper unless he can come up with an explanation he can
test. Ah, the joys of grad school! Good luck, John!

BTW, about the name "ouzel": my Webster's says that it comes from Middle
English *ousel*, Old English *osle*, meaning blackbird; and in some way
this is akin to Latin *merulus* and to Middle French *merle*, also
meaning blackbird.

Burt Guttman guttmanb at elwha.evergreen.edu
The Evergreen State College Voice: 206-866-6000, x. 6755
Olympia, WA 98505 FAX: 206-866-6794