Thayer's Gull (thayeri)

(last update: January 22, 2013)

Thayer's Gull - Plate 4.

From: Identification and Variation of Winter Adult Thayer’s Gulls with Comments on Taxonomy, by Steve N.G. Howell & Martin T. Elliott, IN: Alula 4/2001.

Plate 4. "Adult" thayeri-like primary patterns of birds filmed or photographed in Europe (primaries drawn artificially spread to show inner webs, and grey tones not reproduced accurately beyond subjective relative comparisons among examples shown).

© Martin T. Elliott.

I. Adult Larus sp., Killybegs, Co. Donegal, Ireland, February 1999 (from MTE video). Wing-tip pattern very like thayeri but appeared dark grey in the field, not black enough for thayeri; looked comparatively large and long-billed, and possibly a thayeri x kumlieni intergrade. Note that the full extent of P9 medial band was not discernable.
II. 4th winter (possibly advanced 3rd winter) presumed kumlieni. Hayle Estuary, Cornwall, March 2001 (from MTE video). Upperparts in field estimated at Kodak 4.5-5.0, being slightly darker than argenteus present. Note the virtual lack of dark extending into a medial band on P9-P10, relatively narrow dark subterminal bands and dark outer web streaks on P7-P8, and broken subterminal band on P6. Structurally this bird looked typical of an Iceland Gull.
III. 3rd winter (possibly retarded 4th winter) presumed kumlieni. Plymouth, Devon, April 1998 (from M. Ahmad photos). Comparatively large and long-billed, recalling I in structure; in this plumage it would be difficult to disprove as thayeri. However, P9 is probably too extensively pale, lacking a distinct medial band (which, in same-age thayeri, is usually broad and isolates a mirror, or P9 is mostly dark distally; see Plate 3, I), and the faint markings on P5 (barely visible in the field) would be unusual at this age.
IV. 4th winter type L. a. argentatus. Alkerton, Oxfordshire, December l998 (from MTE video). Similar to thayeri but darker grey above (estimated > Kodak 6.0) and P7-P8 with more extensive black subterminally and on inner webs, and reduced white tongues. It would also be unusual for a thayeri this "immature" to show a broken dark outer web to P9.
V. Adult (4th winter or older) L. a. argentatus, presumed female. Alkerton, Oxfordshire, December 1998 (from MTE video). An extremely thayeri-like pattern, and unusual in its unbroken black outer web to P9. This individual appeared too dark grey for thayeri, and was structurally typical of argentatus; nonetheless, small female individuals could cause identification problems.
VI. Adult (4th winter or older) L. a. argentatus, presumed male. Alkerton, Oxfordshire, December l998 (from MTE video). A typical "northern" type with relatively dark grey upperparts, reduced black on P6-P8, and, compared with thayeri, black restricted on the outer webs of P7-P9 while being too extensive on the inner webs.
VII. Adult (4th winter or older) L. a. argentatus. Parkentin, Germany. September 1996 (from
MTE photos). Again, very similar in pattern to thayeri, and upperparts estimated at Kodak 5.0-.5. Apart from obvious structural differences this individual showed more extensive subterminal black on P6-P8 than is typical for thayeri; as this bird was in moult, P6 pattern was interpolated.