May 1997 Field Journal 7.29 Curlew Sandpiper
Technical Details:
Date Observed: 7/29/97
Observer:
Mark Eaton
1524 36th Avenue
San Francisco, CA 94122
Location:
Stevens Creek Mitigation Pond [Santa Clara], a.k.a the
first pond west of Crittendon Marsh, north of
Moffett Field in Mountain View. When observed, the
bird was at least 100 yards if not further from the
observation point.
Time Observed:
Roughly 6:30 PM through 7:30 PM
Lighting:
Nearly ideal. Cloudless sky and the bird was viewed
from the west, front-lit by the setting sun. Some
possible warming of colors due to natural chromatic
shifts of the setting sun.
Optics:
Nikon Fieldscope ED 60mm, 20-45x zoom eyepieceBelow are my Field Notes, edited only for grammar and clarity. No
field guides were consulted at this point, though conversations were
held with other birders.A shorebird sligthly but distinctly larger than a Western Sandpiper.
Bill noticeabley decurved over the outer 3/4 of the bill,
straigthening at the head. Black spots on the undertail coverts;
belly and undertail coverts otherwise pure white. Pale supercilium;
chin pale when viewed in profile, becoming less pale (more like the
surrounding plumage) when as the viewing angle became more head-on.
Breast splotched with a striking color midway between pale salmon and
rufous; otherwise pure white. Crown finely streaked with light brown.
Back and upperwings pure black with white feather edgings, giving a
scaly appearance. Black legs and dark eye. Primaries extend beyond
tail, obscuring the view of the upper tail and rump. Back of neck
showing very fine dark necklace, extending about 1/2 way down sides of
neck. Pale edgings on primaries.Other notes from memory:
"Very pale wing linings, sharply contrasting with upperwings.
Generally impression is a over-sized peep with a strikingly colored
breast and a relatively long, decurved bill, though perhaps not as
decurved as one might expect. Posture similar to a peep, not nearly
as chunky or as large as a Dowitcher.Discussion:
This is a shorebird intermediate in size between a Dowitcher and a
peep. The blotchy coloration on the breast would tend to indicate a
bird molting out of alternate plumage. The coloration effectively
limits the choices to Red Knot, Sanderling, CUSA, and if we're even
more ambitious, Rufous-necked Stint and Spoonbill Sandpiper. SPSA can
be eliminated immediately due to it's bill shape and RNST can be
eliminated as it has a white breast. REKN can be eliminated by size
and bill shape. Finally, bill shape and the posture, particularly in
the neck area, eliminates SAND from the running.So, we are left with a CUSA. How does this compare with information
found in guides? The NGS guide, 2nd edition, shows a molting fall
adult bird in addition to a breeding bird. The observed bird would
appear to fall somewhere inbetween, with all dark wings, but still
retaining a fair amount of the coloration on the breast. Also, the
observed bird had a slightly less decurved bill than shown in the NGS
guide. Peterson's western guide, 3rd edition, shows the bill more
correctly, but no intermediate plumages between alternate and basic
plumages.Kaufmann's "Lives of NA Birds" has a nice picture of an alternate
plumage bird, including the black spots on the undertail coverts. As
well the feather edgings are nicely shown. This bird did not have any
coloration on the upperwings and had lost much of the coloration on
the head and parts of the breast. Audubon's "Master Guide to Birding"
has another good picture in alternate plumage, though the bill on this
bird had curvature extending farther towards the head, though the
total amount of decurvature was about the same as in the photograph.
Again, there was less coloration on the head and none on the upper
wings, tending to confirm the molting hypothesis.Home
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