Michael,

Maybe so, but we always reason probabilistically. There may well be other
species of kingbirds that occur along the Amazon that look just like these
but that nobody has considered. We don't normally check every Heermann's
Gull to be sure it's not a Gray Gull. But I agree, we should be alert to all
the possiblities. However, the fact that 100% of identifiable specimens and
100% of calling birds have been Tropicals and not Couch's, plus the
biogeographical facts all point to Tropical Kingbird as at least one order
of magnitude more likely than Couch's. So we leave the rest as
Toopical/Couch's for the record, but with a presumption that they are far
more likely to be Tropical than Couch's on the basis of the sample that has
been identifiable. I recall reading that article also and concluding that
the "field marks" were really not adequate to make the discrimination. In
the Yucatan both are common and conspicuously vocal, so I never felt the
need to try to distinguish them by probably broadly overlapping tendencies.

Gene.

At 11:57 PM 10/21/97 -0700, you wrote:
>Hi Tweets,
>
>Gene Hunn writes:
>
>>It is my understanding that it is really impossible to tell Couch's from
>>Tropicals in the field (and often impossible in the hand).
>
>I believe there was an article on the separable marks in Birding a couple of
>years ago.
>
>>The calls,
>>however, are quite distinct.
>
>Thank heavens!
>
>>Of the dozen or so Washington State records,
>>several have been heard vocalizing, and all of these have been Tropicals.
>
>Leading to the circular assumption that...
>
>>There are no Couch's Kingbird records, to the best of my knowledge anywhere
>>in the western half of the continent.
>
>No one looks for Couch's 'cause they're told that these birds are 'all'
>Tropical Kingbirds. Maybe they are, I wouldn't know, but if the alternative
>to Tropical is dismissed out of hand, there's not much sense in looking, is
>there? And nobody else *knows* either. Hasn't *anybody* studied the
>difference on the breeding grounds to apply to these Sep-Nov birds?
>
>So, if an observer doesn't get the calls, and doesn't get the separable
>marks--whatever they are, all I can remember is that Couch's ordinarily has
>a perceptibly larger bill and one of them has a darker auricular; I remember
>thinking there was more difference between them than there is between some
>empids that we *can* identify--where is the justification for calling them
>'Tropical' Kingbird rather than 'Tyrannus sp.'?
>
>If you can't tell, you don't know, therefore can't enter the record simply
>as an assumed ID for two obvious reasons: it screws up the integrity of the
>data by distorting the pattern of whatever the *actual* distribution may
>turn out to be, and ignores that the opposite assumption is equally valid,
>that some of these birds are missed Couch's Kingbirds--after all, they have
>a post-breeding dispersal as well, don't they?.
>
>A third reason is that accepting an ID-by-assumption undermines the
>integrity of Rarity Committee standards wherein a field description not only
>must at minimum establish the identification beyond reasonable doubt but has
>also to eliminate completely all similar species.
>
>Michael Price We aren't flying...we're falling with style!
>Vancouver BC Canada -Buzz Lightyear, Toy Story
>mprice at mindlink.net
>
>
>