Hi Tweets

Stuart MacKay writes:

>With the sunshine this was a stunning bird: bright chestnut crown,
>creamy, yellow supercilium and one feature not noted in the field guides
>- bright chestnut tertials - apparently the whole feather not simply
>edging.
(snip)
>- that sharp-tail is a must see.
>Definitely the most beautiful shorebird I've ever seen.

I'll hoist one to that! They're stunning.

Stuart, I've been using that tertial pattern difference on the brighter
Sharp-tailed Sandpipers (SHSA) as a point of comparison for so long it just
never occurred that it might not be in the books. As soon as I read your
remark, I went through all my field guides and shelf books and, by gum,
you're right, not even the workhorse 'Guide to Identification and Aging of
Holarctic Waders' (Prater et al)--there's only one that does: Dennis
Paulson's Shorebirds of the Pacific Northwest, wherein he writes: "broader
and slightly paler tertial fringes in SHARP-TAILED, producing a very
brightly marked back (bright PECTORALS overlap with less bright
SHARP-TAILED), often the best way to pick out a SHARP-TAILED in a flock of
PECTORALS when all are foraging with their heads down."

While I've never seen a SHSA with the *entire* tertial bright rufous, the
black feather center of the longest tertial is usually reduced to a long
thin black oval within very broad bright fringes; the fringe is the main
component of the pattern. Though some of the dullest juv SHSA individuals
can have thinner, duller fringes, they seem always to be wider than any
Pectoral Sandpipers (PESA), in which the feather center, not the fringe, is
the larger component of the feather pattern. It may be possible to
generalise that this is a consistent ID mark in the complex of fieldmarks
used to separate the two species.

Reading on in Dennis' species account on SHSA, where he says in the 'Notes':
"Contrary to Farrand (Audubon Society Master Guide to Birding, 1983)...That
book also calls the Sharp-tailed a geographic replacement for the Pectoral
in Siberia; in fact, their breeding ranges overlap entirely. Presumably the
two species diverged in isolation on the two continents, then the Pectoral
reinvaded Siberia as a breeding species and now breeds even west of the
westernmost Sharp-tailed."

I wonder about this. When two species derived of a common ancestor reunite
(the interglacial period began at the same time for both), isn't there
usually a massive wave of hybrids (Nature anticipates a soap-opera plotline:
but, John, I remarried because you've been missing for so many years! Mary,
how could you! etc. '-), then replacement of one by the more aggressive
other? If they're divergent, why aren't we seeing this? I read somewhere
that gulls and shorebirds are fairly closely related---and looking at the
juv gull plumages, particularly those of the small hooded gulls, I can
surely believe this--but if this is so, why are shorebirds so stably
speciated, so resistant to hybridism, while gulls continually establish new
frontiers to the term 'parentage'?

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