American Herring Gull (smithsonianus)
(last update: October 12, 2011)
American Herring Gull 1cy October
The issue of Dutch Birding 26: 1-35, 2004 contained a very comprehensive paper on the identification of smithsonianus, titled: Identification of American Herring Gull in a western European context. It was written by Pat Lonergan & Killian Mullarney. The outstanding text is copied on this webpage, with links now added to various Canadian birds photographed throughout the months. When appropriate, more details from recent field research has been added as well. Full PDF download: HERE.
"we" in the text below refers to the original authors.
If any errors occur in this text, please let me know and mail to marsmuusseatgmaildotcom.
Identification of American Herring Gull in a western European context
|American Herring Gull (smithsonianus) 1st cycle (2CY), January 29 2012, Daytona beach- Florida, US. Picture: Mike Watson.|
|European Herring Gull (argentatus) 1st cycle (1CY), November 19 2013, Katwijk beach, The Netherlands. Picture: Mars Muusse. Dark on upperparts and lack of obvious notching on tertials.|
With more than 90% of the records of smithsonianus in Europe being made up of birds in first-winter plumage, this is certainly the best-represented plumage type on the European side of the Atlantic, At least in Ireland, where the vast majority of European Herring Gulls are of the paler argenteus type, first-winter smithsonianus can be rather conspicuous amongst a mid-winter gull flock, Smithsonianus appears to exhibit even more individual variation than argenteus of the same age but even so, we had difficulty finding birds in the eastern USA that would not attract some attention in a routine search of a gull flock on the European side of the Atlantic.
Many of the characters which help differentiate juvenile smithsonianus and European Herring Gulls, most notably those relating to the upper- and undertail-coverts, wings and tail, remain essentially unchanged in first-winters and therefore do not need to be repeated here. Additional characters on which to concentrate when confronted with a possible first-winter smithsonianus include:
Uniformity of underparts By mid-winter, many first-year smithsonianus are a little faded and less evenly dark than they would have been as juveniles but are still more uniform below than the great majority of European Herring Gulls. The latter generally have paler, more mottled or streaked underparts but can occasionally be more uniform (and consequently darker looking), thus resembling smithsonianus (plate 21 and 34).
Solid darkness on lower hindneck and upper mantle Typically, smithsonianus exhibits a more uniformly brownish lower hindneck and upper mantle that merge with the uniform brownish underparts.
Greyness of breast-sides and flanks As part of the post-juvenile moult of body-feathers, many first-winter smithsonianus acquire plain, contrastingly slategrey-coloured feathers on the breast-sides and flanks, gradually extending to the rest of the underparts. Possibly because of their usually more mottled underparts, European Herring Gulls undergoing the same moult show much more subtle contrast between the old (brownish) and new (more greyish) feathers.
|American Herring Gull (smithsonianus) 1st cycle (2CY), January 13 2012, Portland, Maine. Picture: Bill Bunn.|
|European Herring Gull (argenteus) 1st cycle (2CY) YUAC February 09 2013, Calais, NW France. Picture: Jean-Michel Sauvage. Cassic: streaked on neck, mottled on underparts, piano-key pattern on greater coverts, notched tertial fringes (worn here) and pale on undertail coverts.|
Pale-headed appearance Many smithsonianus acquire a pale head in late winter as a result of wear (Howell 2001) and due to their dark body this feature may draw attention to a smithsonianus among a flock of European Herring Gulls. The importance of this feature has been overstated a little as only a small proportion really is pale-headed and darker-bodied European birds are likely to also occasionally look pale-headed for precisely the same reasons. European Herring Gulls from the eastern Baltic area are often strikingly pale-headed in winter (Klaus Malling Olsen pers comm).
Scapular pattern The range of individual variation in first-winter scapular-markings exhibited by both smithsonianus and European Herring Gulls, and the degree of overlap, make it very difficult to identify any particular patterns that might be considered ’exclusive'. There are, however, certain characteristic patterns in smithsonianus that are not so usual in their European counterparts. It is important, here, to distinguish between often-retained juvenile scapulars (usually, the rearmost larger feathers), which are plain, brownish, somewhat worn and with pointed tips, and (freshly) moulted first-winter feathers, which have broader, more rounded tips. The most distinctive of these (again, usually seen among the larger rearmost and lower row(s) of feathers) are rather dark and plain, with or without a diffuse darker centre (plate 38). Due, perhaps, to a tendency in many smithsonianus for the post-juvenile moult of the scapulars (in which the juvenile scapulars are replaced with first-winter feathers) to be a rather protracted process, there is often more of a variety of scapular patterns in the one bird than is generally the case in European birds; the explanation for this is that the appearance of feathers in the same generation can change depending on the time of year they are moulted (Howell 2001). In most European Herring
Gulls, the pattern of the first-winter scapulars tends to be rather consistent, each individual feather exhibiting much the same markings as the next, the overall effect being of a series of regular transverse pale and dark bars. However, there are many exceptions to these general tendencies and, at best, certain scapular patterns should be regarded as offering little more than marginal supporting evidence in the identification of vagrant first-year smithsonianus in Europe.
Underwing-coverts The uniformity of the axillaries (especially) and underwing-coverts, and the general ’smokiness' with a lack of obvious patterning, can be striking in smithsonianus. In argentatus and argenteus, these areas tend to be paler in tone and more mottled in texture. The underwing-coverts of graellsii, however, can be very like smithsonianus but several other differences from smithsonianus (see above) usually preclude serious confusion.
Bill-colour There is a tendency for both smithsonianus and argentatus to develop a pale base to the bill quite early in their first winter, with the most extreme birds approaching first-year Glaucous Gull in this respect. In argenteus, the contrast in the bill pattern tends to be more subdued until later in the winter.