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Yes, I saw those photos, but none of them show notching as deep as that
portrayed in plate 4, #11 (White-rumped) in Turner & Rose.  The photos
showing the clearest views of White-rumped are the third and fifth in the
series.  These views match the figures in the guides I mentioned in my post
(and not the illustration in T & R).  Also recall that the text of T & R
does not match their illustration, but does match illustrations and
descriptions of the other guides I cited before.  Which part of T & R is
accurate...?

Or are you suggesting that the photo of Mangrove Swallow on the web page you
mentioned is representative of that species?  That photo shows a short,
square (unforked) tail (molt?), which does not match the descriptions or
illustrations in field guides (or the Viera swallow, for that matter).  And
the photo I mentioned in Dunning shows a nearly square tail in a
White-rumped as well.

Most characters vary to some degree among conspecific individuals.
Moreover, assessing the degree (depth) of forking in the tail in the field
or from photos is complicated by viewing angle, and by the degree to which
the feathers of the tail are spread out (or "clamped together")... compare
the top two photos of the Viera bird on this page:

http://hometown.aol.com/jpuschock/masw5.html

Moderately forked or not at all?  (And is the degree of forking in the upper
right photo significantly different from that in the fifth photo of
White-rumped on the Philadelphia page you linked above?)

As the lateral rectrices are pulled more and more medially (long axes of
rectrices become closer to parallel) , the angle of the fork/notch becomes
more and more acute, and looks progressively deeper; this effect is
exaggerated by lateral foreshortening in some viewing angles.

If the average tail of an White-rumped really is more strongly forked than
the average tail of a Mangrove, it is not apparent from evidence I have
seen. (And the two people who pulled specimens out [so far] to compare these
species apparently did not notice a big difference in the tails.)  And for
reasons mentioned above, even if there is a difference, unless there is only
a small degree of overlap between the two species in this trait it would be
tricky to use in the field (or from photos).  Be that as it may, I will be
delighted if someone shows that this character really can reliably be used
to distinguish these species (and ID the Viera bird)... perhaps the authors
of the guides I consulted overlooked this (or thought the ID was
straightforward enough without it).

David Wright
Miami Shores

PS: I'm betting on the Viera bird being a Mangrove, but not because of its
tail.

on 11/27/02 2:28 PM, John H Boyd III at [log in to unmask] wrote:

> I think you should examine the photos from the VIREO collection at
> http://www.acnatsci.org/~wechsler/lightbox/ID-FRONT/SWALLOWS.html.  These
> seem to support Turner & Rose.
>
>> Degree of forking/notching of the tail has been cited as a character that is
>> useful for distinguishing Mangrove and White-rumped swallows.  Apparently
>> this notion is based on the illustration of White-rumped in Turner and Rose
>> (1989; Swallows and martins), where it is shown with a deeply forked tail.
>> The text descriptions in that book, however, describe both White-rumped and
>> Mangrove as having "slightly forked" tails.  Ridgely and Tudor (1989; Birds
>> of South America. Vol. 1, oscine passerines) do not mention the tail of
>> White-rumped being different those of other *Tachycineta*, and it is
>> illustrated as being only modestly forked.  Narosky and Yzurieta (1989;
>> Birds of Argentina and Uruguay) say of *Tachycineta*, including
>> White-rumped, "tails barely forked," and their illustration matches that
>> description.  Finally, the photo of White-rumped in Dunning (1987; South
>> American birds: a photographic guide) shows very little (if any) notching of
>> the tail.  Also notable in this photo are the tertials, which show only a
>> slight hint of white tips.
>>
>> Degree of tail forking thus does not appear to differ significantly between
>> the two species.
>>
>> David Wright
>> Miami Shores
>>
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> John H. Boyd III                               [log in to unmask]
> Dept. of Economics                             Phone: 305-348-3287
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