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| preface to the descriptions: variability in gull plumages |  As an example of variability, these two feathers are both P6 from a Western Gull-- from the same Western Gull (one from each wing)! The one with more dark in the tip has a more typical pattern for P7, but, trust me, it really was P6. Photo by Steve Hampton, 2000. |
All of my gull descriptions at this website should be prefaced with WARNING: PLUMAGES MAY VARY . Yes, gulls, in addition to going through up to 11 semi-identifiable molt sequences between juvenile and a 5th year adult, and countless inbetween stages, are also quite variable from bird to bird, even when at exactly the same stage of molt (oh, and molt timing may vary from bird to bird too). And I'm not refering to the numerous hybrids here. The plumage descriptions should be taken as general, not precise. Almost all aspects are variable. When I say "variable" in the plumage descriptions, that means "highly variable".
Nevertheless, some things are more variable than others, and learning this is a good step, so that, when trying to identify a strange gull, you can focus on the important aspects and ignore the less important parts. Even so, your odds of finding a bird in a large gull flock that totally fails to match any of my descriptions is probably about the same as finding a pigeon at Trafalgar Square. That said, I hope the chart here is useful.
This applies to four-year gulls; for 3-year gulls, the general rules below apply, with first year for the first, second and third for the second year, and adult for the adult.
VARIABILITY CHART
| SIZE: males may be much larger than females, and runts are apparently possible, but in general a good field mark when comparing species of obviously differing sizes | ||||
| BILL SHAPE: males have larger bills than females, but in general a good field mark with little variation when comparing species with big differences-- once you get to know the shapes | ||||
| HEAD SHAPE: yikes, highly variable due to viewing angles and the way the feathers are sitting; be careful here | ||||
| WING EXTENTION: a good mark; watch out for worn primaries that make them shorter, or wings held at funny angles | ||||
| JUV/FIRST WINTER | SECOND WINTER | THIRD WINTER | ADULT WINTER | |
| BILL COLOR: | generally reliable, with variation rare in most species; more variable by spring | high variability | high variability | low variability, but changes may occur between summer and winter |
| LEG COLOR: | the shade of pink is highly variable | high variability | high variability | brighter in spring, but the pink vs. yellow question is reliable, with very few exceptions (but watch those lighting conditions) |
| IRIS/ORB RING: | dark-- and that's reliable | high variability | high variability, but usually like adult | reliable, with exceptions rare (in most species; e.g. high variability in Thayer's) |
| HEAD: | high variability | high variability | high variability | high variability |
| UNDERPARTS: | high variability | high variability | high variability | white |
|
PRIMARIES (folded): |
a good mark, but beware of wear and tear | a good mark, but beware of wear and tear | a good mark, but beware of wear and tear; A-spots highly variable | a good mark, but beware of wear and tear, especially on those A-spots |
|
PRIMARIES (in flight): |
a good mark, but beware of lighting conditions | some variability | high variability | can be a good mark; limited variability, generally noted in the descriptions; beware of worn primaries |
|
SECONDARIES (in flight): |
reliable | moderate variability | moderate variability | reliable |
| TERTIALS: | moderate to high variability, depending on species | high variability | high variability | fairly reliable, but the crescent size subject to feather wear |
| GREATER COVERTS: | high variability on many species; a potentially useful tract, but takes some experience | high variability | high variability | adult gray |
| LESSER & MED COVERTS: | moderate variability and subject to wear | high variability | high variability | adult gray |
| SCAPULARS: | moderate variability and subject to wear | high variability | high variability | adult gray; that white crescent may vary with feather wear and viewing angle |
| BACK: | moderate variability and subject to wear | high variability | generally adult gray; some variability | adult gray; for variability see the shades of mantle gray page |
| RUMP: | small variability | moderate variability | moderate variability | white |
| TAIL: | limited variability with exceptions rare, making it an excellent field mark for ruling out species | moderate variability | moderate variability | no variability |