ML611912184

Age

Not specified

Sex

Not specified

Observation details

***mega; first record for Atlantic Ocean; First spotted by Frank Gallo; studied closely by all leaders: Frank Gallo, Paul Guris (trip leader), Andrew Guthrie, Richard Guthrie, Shaibal Mitra, and Angus Wilson; also by many participants on the pelagic. Copiously documented via multiple sets of photos and analyses. The following represent my actual field impressions, some discussion of several distinctions between these and later analyses that were based more directly on photos, and some discussion of the the subspecies identity and route of vagrancy for this singular record. In some respects, our live field impressions provided better insights into the bird’s actual appearance than did the photos, particularly regarding mantle tone. Original notes: As soon as the bird’s pink legs were noted, I carefully checked several field-observable characters against those expected for Lesser Black-backed Gull: 1. Overall structure: the bird did NOT show the rakish, long- and slim-winged outline of Lesser Black-backed Gull. 2. Iris color: despite being an immaculate adult, the bird’s irides were decidedly NOT as clear and pale as in Lesser Black-backed Gull. 3. Bill color: the red gonys spot was clearly smaller than in Lesser Black-backed Gull (but note that I didn’t discern the small dark mark on the lower mandible in the field). Other important characters were also noted in the field, including some that were easy to judge: 4. Foot color: bright pink—much brighter than in Herring or Great black-backed Gull. 5. White trailing edge of wing/tertial crescent: very broad, as in Western or Slaty-backed Gulls. —and some that were more subtle: 6. Wingtip pattern: this was a point where field impressions were decidedly inferior to subsequent photo analysis, but I made a conscious point of noting the bird’s extensive black wingtips and noting that these were counter-indicative of Slaty-backed Gull. 7. Mantle color: under careful, conscious scrutiny, the bird appeared darker to me than a graellsii Lesser Black-backed Gull. The various photos show a huge range in exposures, but it was and remains my opinion that the bird’s mantle was toward the darker end of variation in Western Gull. It is my hope that these notes contribute to documenting the actual appearance of this bird, especially in terms of nuances of shade that were not reliably pinned down by the photos. If one accepts the unanimous opinion of the field observers—that this bird’s mantle was darker than that of a typical graellsii Lesser Black-backed Gull—then serious consideration ought to be given to the subspecies wymani for this bird. Details of the bird’s wingtip pattern, especially the solid black subterminal mark on p5 and the broken mark on p4, are also more typical of wymani than of occidentalis. Although it could be argued that occidentalis, as a longer-distance migrant, is a better candidate for long-distance vagrancy than is wymani, it is not clear to me that this model of vagrancy (analogous to that of Glaucous-winged Gull) is appropriate in this instance—especially given the paucity of records of occidentalis at even moderate distances inland from its coastal distribution. In contrast, the prior occurrence of Western Gull in Texas suggests that a low latitude crossing to the Gulf of Mexico is a plausible model of Western Gull vagrancy to the Atlantic Basin, and one perhaps more likely to involve wymani than occidentalis.

Technical information

Model

Canon EOS 10D

ISO

200

Focal length

400 mm

Flash

Flash did not fire

f-stop

f/5.6

Shutter speed

1/1000 sec

Dimensions

3072 pixels x 2048 pixels

Original file size

1.44 MB