> Loons
>and Grebes are in different orders, whereas all of the perching birds
>are in a single order. Are loons and grebes really more different from
>each other than swallows are from finches or ravens or shrikes?

In a word, Yes. Quite a lot more different from each other, in anatomy, DNA
hybridization results etc. - they are probably not closely related at all.
The Sibley-Monroe classification, though it includes both loons and grebes
in a huge Order Ciconiiformes that also includes seabirds, shorebirds,
herons, birds of prey etc., associates grebes with tropicbirds and boobies
and loons with tubenoses, penguins and frigatebirds. Whether you buy this
or not I think most ornithologists would not consider loons and grebes to be
very close.

Are
>the ranks supposed to indicate the evolutionary time of splitting, or
>the genetic difference? They can't successfully convey both.

The Sibley-Monroe classification assumes that you can do just that , as
(they argue) the background mutation rate of DNA provides a sort of
molecular "clock". I know this has been criticized but I am not
knowledgeable enough to analyze this further.

>Consider the case of the Western Flycatcher, where birders thought
>there was one species, but the birds thought otherwise. If we don't
>change the way we refer to these birds, we miss a point that is
>apparently very important to the birds themselves.

There is a considerable difference between biological species such as these
flycatchers, which most biologists would, I think, accept as real entities
having some meaning in nature, and the other heirarchical categories such as
genus or family.
--
Ronald I. Orenstein Phone: (905) 820-7886 (home)
International Wildlife Coalition Fax/Modem: (905) 569-0116 (home)
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