Hi Tweets,

Gene Hunn writes:

>Maybe so, but we always reason probabilistically.

Heh, I can just hear the words of Mr. Chapman, my ever-hopeful high school
History teacher to whom I was a constant despair: Michael, never leave a
generalisation just *sitting* there without its qualifier. I sometimes
reason probabilistically as well, Gene--and pay for it as I get plucked
clean by someone with three jacks. '-) Sure, sometimes it's the reasonable
thing to do in the circumstances. But not when there's the possibility of
two extremely similar species with post-breeding dispersals, only one of
whose is at all defined.

>There may well be other
>species of kingbirds that occur along the Amazon that look just like these
>but that nobody has considered.

True, and I guess it behooves us to have some passing knowledge of these
birds too, so that if a bird from far, far away does appear, such as
Toronto's Variegated Flycatcher, we're not totally unprepared for the
possibility.

>We don't normally check every Heermann's
>Gull to be sure it's not a Gray Gull.

Oh, dear; they're *not* Gray Gulls? Well, *that* explains their unusual
distribution in North America. '-)

>(snip) 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.

I'm not trying to be stubborn here, Gene, just clear: I don't know how big
the total sample size is, nor what proportion of known birds there are
within it, so I don't know if that degree of likelihood is so.

>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.

Yeah, agreed: it's more like seeing a silent Alder/Willow Flycatcher migrant
in habitat atypical for either; most of us would have no hesitation calling
it an Empid sp., not saying, well, most here are Willow, therefore... If
you don't know the diagnostic point(s), such as voice, you can't call it. If
they don't open their mouths, they're not even Tropical/Couch's, but
'Tyrannus sp.'

>I recall reading that article also and concluding that
>the "field marks" were really not adequate to make the discrimination.

Could you elaborate, just in case a well-described Tropical/Couch's-type
report comes across my desk? If I'm using something that's discreditable,
then I need to know that so I can assess these rarity reports fairly.

>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.

Aaauuugh, that "probably" hedge! You're dismissing these marks but you don't
*know*! Heh, this should be the intro to an episode of Mission Impossible:
your mission, Gene--should you wish to accept it-- is to go back to the the
Yucatan...

Twist his rubber arm... '-)


Michael Price We aren't flying...we're falling with style!
Vancouver BC Canada -Buzz Lightyear, Toy Story
mprice at mindlink.net