ML613282930

Age and sex

Adult, Unknown sex - 1

Behaviors

Flying

Media notes

Adult

Observation details

[European] Common Gull v. Short-billed Gull Identification Reference - "Identification of the Larus canus Complex" Adriaens and Gibbins | "Mew Gull is now two species! How to identify Common Gull and Short-billed Gull" Sibley | "Gulls: A Guide to Identification (second edition)" Grant | "Seabirds: The New Identification Guide" Harrison. Age of Picton Marina Bird - Adult, by absence of black on alula and primary coverts. Plumage - Winter/basic, by dark head markings. Size - Slightly smaller than Ring-billed Gull. Inconclusive for identification. Common Gull is slightly smaller than Ring-billed Gull and slightly larger than Short-billed Gull. Adriaens & Gibbins (hereafter A/G) note (page 7) that "There are average differences in size and shape between the … taxa that may be helpful in the field at times, although there is a lot of variation and overlap. Interpreting what are often subtle differences in the field may require extensive experience with all four taxa. It should also be kept in mind that there is a notable size difference between males and females, sometimes even more so than between the taxa." With this uncertainty, and my own minimal comparative experience with the two species, I draw no conclusions from the Picton bird’s size. Structure - Slightly more delicate than Ring-billed Gull. Inconclusive for identification. Common Gull is described as more delicate than Ring-billed Gull, but having a relatively blockier head than the “cuter” Short-billed. With minimal comparative experience with the two species I draw no conclusions from the Picton bird’s structure, except to note that its forehead to crown angle is not totally dissimilar to the nearby Ring-billed Gulls. Mantle - Slightly darker than Ring-billed Gull. Inconclusive for identification. Sibley notes mantle colour is "palest on European Common Gull (close to Ring-billed Gull)" and "Short-billed Gull is ... quite dark gray on average, usually distinctly darker than Ring-billed Gull. But mantle color is variable and not particularly reliable for separating these taxa.”. A/G state (page 7) "There is a lot of overlap between the taxa in the tone of this [mantle] grey (figure 2), so it is not a very useful character ..." Head Pattern/Flanks - Head pale with grey/brown specks/streaks on the crown and behind the eye, with larger dots on the nape and neck. Flanks unmarked. Indicative of Common Gull. A/G state (page 8) that Common Gull in winter "looks variably streaked, especially on the crown, nape and ear-coverts, with any pattern on the neck often rather smudgy brown. The pattern may extend onto the breast.” They note further that Short-billed “… are the most distinctive. Adults have an extensive brown wash across the neck in winter, which ... tends to be smoothly textured rather than heavily blotched. The brown wash often extends onto the flanks.”. The clean-flanked and pale-headed (lightly streaked and blotched) appearance of the Picton bird is indicative of Common Gull. Bill - Dull yellow/green (more yellowish at tip) with muted but complete dark band. Indicative of Common Gull. The base bill colour of winter Common and Short-billed Gull are similar (A/G page 17). ~75% of Common have a complete dark band, with 25% showing a broken band extending across both mandibles (A/G Diagram Two). 65% of Short-billed have no band or a band on one mandible only. The complete but muted dark band on the bill of the Picton bird is indicative of Common Gull. Eye Colour - Dark. Suggestive of Common Gull ~ 85% of Common Gulls have a dark iris. ~ 60% of Short-billed Gulls have pale eyes (A/G Diagram 1). The Picton bird had dark eyes, which points towards Common Gull. Primaries (Black V versus Black Triangle) - Black triangle. Indicative of Common Gull. Sibley notes that the black on the wings tips of Common Gull presents as a large black triangle, whereas the same black wing tip pattern on Short-billed Gull is described as a V, with the grey basal areas and a white “string of pearls” (Harrison page 133) at the base of the outer primaries protruding deeply into the black tip (see images 32 and 33 A/G page 22). The wing tips on the Picton bird presented as a black triangle, indicative of Common Gull. Primaries (Colour Below Tertial Tips on Standing Bird) - Visible primaries below tertial tips black. Indicative of Common Gull. The exposed primaries on a standing Common Gull are black from just below the tertials to the end of the wing, no grey is visible. Conversely, "On a standing [Short-billed Gull] [the reduced black in the primaries] often leave a very extensive grey basal area of the wing-tip visible just below the tertials, which may extend clearly beyond the tertial-tips; this impression is unlike in the other three taxa…" . (A/G page18)(see image 29 on page 22). On the Picton bird the exposed primaries below the tertials are black, not grey, indicating Common Gull. Primaries (Inner) - White tips on inner primaries distinctly narrower than white tips on secondaries. Indicative of Common Gull A/G state (page 19) that on Common Gull "the inner primaries generally have only narrow white tips, clearly much narrower than the white trailing edge to the secondaries, whereas "What also makes the primary pattern of [Short-billed] distinct from the others is that the inner primaries usually have broad white tips (nearly as deep as the white tips to the secondaries)." The white tips on the inner primaries of the Picton bird are strikingly narrower than those on the secondaries, indicating Common Gull. Primaries (Individual) p9 - Black on outer web reaches primary coverts. Indicative of Common Gull. On Common Gull the black outer web of p9 often reaches the primary coverts, whereas on Short-billed Gull it does not (Sibley). The black on p9 on the Picton bird reaches the primary coverts, indicative of Common Gull. p8 - More than 2/3rds black, no white at tongue tip, no white mirror. Indicative of Common Gull. Sibley indicates that on Common Gull the black on the outer web of p8 covers most of the length of the feather, whereas on Short-billed 1/2 or less of the feather is black. The outer web of p8 on the Picton bird is 2/3rds or greater black, indicative of Common Gull. A/G state (page 16) that ~80% of Short-billed Gull show a broad white spot at the p8 tongue tip, whereas ~85% of Common Gull show no white here. The Picton bird showed no white, indicative of Common Gull. Note: ~25% of Common Gulls and 0% of Short-billed Gulls have a white mirror on p8. The presence on the Picton bird of a white mirror would eliminate Short-billed but its absence is indeterminative. p7 - More than 1/2 black, indicative of Common Gull. Sibley states the black on the outer web of p7 on Common Gull covers at least half length of feather, whereas on Short-billed Gull the black usually covers less than half of the feather. p7 on the Picton bird is well more than half black, indicative of Common Gull. p5 - Narrowly incomplete, asymmetrical black band. Indicative of Common Gull. Harrison states (page 131) that black typically extends to p5 on Common Gull, though usually as an incomplete black band (Sibley), with ~20% showing a complete, symmetrical black band and ~10% of birds showing no black markings at all (A/G page 19). Short-billed Gull usually (~90%) has a complete, symmetrical black band on p5. The Picton bird presents an asymmetrical black band split by a shaft of white. Indicative of Common Gull. See Macaulay Library ML144916811 p4 - No black. Indicative of Common Gull. Common Gull almost never (~90%) has black on p4, whereas slightly less than half of Short-billed Gull have some black on this feather (Sibley). The Picton bird had no black on p4, indicative of Common Gull.

Technical information

Model

Canon EOS 90D

Lens

EF600mm f/4L IS III USM

ISO

800

Focal length

600 mm

Flash

Flash did not fire

f-stop

f/5.6

Shutter speed

1/2500 sec

Dimensions

4000 pixels x 2667 pixels

Original file size

2.46 MB