American Herring Gull (smithsonianus)

(last update: October 30, 2015)

American Herring Gull adult February

The issue of Dutch Birding 26: 151-179, 2004 contained a very comprehensive paper on the identification of adult smithsonianus in a European context, titled: Identification of adult American Herring Gull. It was written by Peter Adriaens & Bruce Mactavish. The outstanding text is copied on this webpage, with links now added to various Canadian and European birds placed on the ORG-website. When appropriate, more details from recent field research has been added as well. Full PDF download: HERE.

Identification of adult American Herring Gull
-Peter Adriaens & Bruce Mactavish-

BACK TO PART 1: INTRODUCTION & GENERAL COMMENTS

THIS PAGE IS PART 2: DETAILED PRIMARY DESCRIPTION

Less reliable but possibly helpful characters

HEAD STREAKING This character is really variable in herring gulls but may at times provide an additional clue. In general, adult NF smithsonianus have strong head streaking that reaches far down, well onto the breast. The streaks may be so strong, that they converge into solid brown blotches, especially on the lower hindneck, breast and around the eye. In such cases, the head pattern may be similar to that of nominate Glaucous Gull L hyperboreus hyperboreus, and contrast strongly with the pale grey upperparts. The breast-sides of such birds are often isolated from the fore-wing by a white wedge near the wing-bend (which recalls, with a little bit of imagination, the white wedge of Common Sandpiper Actitis hypoleucos and Spotted Sandpiper A macularius). ln some birds, the streaking or blotching is more prominent on the lower hindneck/breast than on the head itself. A complete necklace of strong streaks/blotches may be present on these pans. The heavy streaking often makes the pale eye stand out very clearly, enhancing the ’mean’ facial expression. There is sometimes a dark greyish or brownish smudge just in front of the eye, sometimes even surrounding the eye, which emphasizes the paleness of the iris. This is usually less pronounced in European Herring Gull. In argenteus, winter streaking is usually slightly thinner, and does not reach as far down, instead being mostly confined to the head and (upper) neck. There are quite a few exceptions, though.
Also, beware of subadult birds, which often show heavier and more extensive streaking than adults, for a longer period of time. NF smithsonianus appear to moult later than argenteus, and this may create an additional difference in head pattern in late winter. Adult argenteus start to acquire a pure white head from late December onwards; by mid-February, most adult birds are entirely white-headed. NF smithsonianus, on the other hand, start losing their head streaking only from late January on. In mid-February, 99% of all adults still retain head streaking. Only by late March have all adults acquired pure white heads. However, it should be noted that moult is not really an identification criterion that can be applied to a single bird, especially if it is a vagrant. For example, it is quite conceivable that a bird having arrived in Ireland in autumn, may start its spring moult earlier than usual due to the more temperate weather conditions than in Newfoundland. In addition, argenteus from Iceland moult later than those from Western Europe (Olsen & Larsson 2003).
Eastern Baltic Herring Gulls also show only thin and limited head streaking in winter (Visa Rauste pers comm) but in mid autumn (October-November) they usually have a distinctly dark-streaked head and neck (Jonsson 1998). In argentatus and intergrades, the winter pattern can be more extensive, and variation can be bewildering.

STRUCTURE This may provide another clue, although the differences are subtle and there is much variation. NF smithsonianus usually have a somewhat ’awkward’ structure, caused by the rather bulky body on short legs. The head shape is angular, with a rather flat crown. In these respects, they are similar to argentatus. The bill is often quite long and parallel-sided, with only a slight gonydeal angle. In argenteus, the head is usually more pear-shaped, and the bill is slightly shorter, with a more marked gonydeal angle. Eastern Baltic Herring Gulls can be more different still, as they have on average rather long legs and an elongated body with fairly long primary projection Mierauskas & Greimas 1992, Jonsson 1998). Note also that NF smithsonianus are fairly large on average, being for example slightly larger than birds of the Niagara population (Jonsson & Mactavish 2001). They may therefore stand out as slightly larger in a flock of argenteus (not argentatus), but there is some overlap.

BILL COLOUR In winter, this may be another element of limited help, as the bill is rather dull in adult NF smithsonianus, compared with adult argenteus. While the bill-tip is normally yellow, the basal two thirds are often clearly less brightly coloured, and may even be greenish, pinkish, or greyish without a yellowish hue. Many winter adults have dark subterminal bill markings, such as a greyish or blackish spot or bar above the gonys. The red gonys spot is often distinctly small, obviously not reaching up to the lower cutting edge, and is rather pale (more orange than red). Therefore, the bill pattern resembles that of argentatus although the gonys spot may be even smaller. In winter, adult argenteus usually retains a more yellowish bill throughout (although the basal two thirds may be paler yellow than the tip), dark subterminal markings are more often absent, and the gonys spot is larger (reaching up to or almost up to the cutting edges) and brighter. Beware of subadult birds, however. From mid-February onwards, the bills of NE smithsonianus rapidly turn bright yellow as head streaking disappears. However, the dark subterminal marks often remain into May at least, which only exceptionally occurs in European Herring Gulls. The orange gonys spot may increase in size and brightness, although it remains relatively small in quite a few birds.

LEG COLOUR Legs are nearly always pink (dull pink to brownish-pink in winter). There is a tendency for the legs to brighten up in mid-February to March and a vague yellowish tinge becomes apparent on a very few birds but is nothing like the yellow of, eg, a Lesser Black-backed Gull L fuscus graellsii. NE smithsonianus with distinctly yellowish legs are truly exceptional, while many Eastern Baltic Herring Gulls, some northern argentatus, and a few argenteus (especially in spring) show this colour. In argenteus, any yellow tinge to the legs often coincides with the development of a brighter yellow bill and pure white head in February-March, indicating that this yellow colour is a signal in breeding birds, and therefore not very likely to occur in smithsonianus vagrants. In Europe, a distinct yellowish tinge on the legs should be considered a sign that the bird is not a smithsonianus.

SIZE OF WHITE PRIMARY TIPS In many argentatus, and in some intergrades and Eastern Baltic Herring Gulls, the size of the white primary tips at rest is also slightly different, being quite large to very large, and creating more white than black in the folded wing-tip. In NF
smithsonianus, the white tips are typically smaller, being close or identical in size to those of argenteus, although there are some adult birds with larger white tips.

FLIGHT Even in flight, several useful clues will be visible in the field. Because the pale tongues are generally longer and broader than in argenteus, the primary pattern often gives a different impression. When seen from below, the outer hand usually appears ’hollowed out’, with the black colour concentrated on the outer and trailing edges, creating a distinct L-shape reminiscent of adult Pontic Gull (figure lb and 2b; plate 229). While a similar pattern is seen in many argentatus, intergrades and Eastern Baltic Herring Gulls, argenteus normally shows more black on the inner web of P8-P10, creating more of a solid black triangle on the underside of the wing-tip (figure 4b). Even from above, the pale tongue is often easily visible on all of the outer primaries, except the outermost (P10). Again, argentatus, intergrades and Eastern Baltic Herring Gulls can be similar, but in most argenteus at least two outermost primaries (P9-P10) appear solidly black (unless the primaries are fully spread, eg, when the bird is landing). Quite a few NE smithsonianus show broad white tongue-tips on P5-P8 (sometimes referred to as a ’string of pearls'), and this creates the impression that the white trailing edge of the wing continues across the black pattern of the outer primaries. This 'string of pearls' was not found in our sample of argenteus but it is shown by some argentatus, Eastern Baltic Herring Gulls and the occasional intergrade. The primary pattern is described in much more detail in the next section.
In conclusion, it will be possible to locate a potential smithsonianus by looking at several subtle characters in combination. The biggest pitfall is perhaps formed by intergrades argenteus >< argentatus. While these are unlikely to show many of the above characters in combination, only detailed analysis of the primary pattern (on the basis of photographs/video) will rule them out conclusively - which is the next step in the identification process.

How to be sure of adult smithsonianus ID?

As Lonergan & Mullarney (2004) have already pointed out, the number of identifiable smithsonianus decreases with age. This is certainly true for adults; our estimates indicate that about 40% of adult NF smithsonianus can be identified with certainty in Europe. This is only a minority, which is unfortunate perhaps, but that is just how it is. The rather large percentage of non-identifiable birds can be explained by extensive variation in both American and European Herring Gulls. While the primary pattern is the key to the identification problem, it is also variable: it varies regionally and individually and is also age-dependent, since the amount of black in the primaries seems to decrease slowly with age (Coulson et al 1984; pers obs on colour-ringed birds). It is sometimes claimed that the variation is also sex-dependent but we have seen no strong evidence yet of this. In fact, several authors who previously searched for sex-dependent variation in the primaries of European Herring Gull, could not find any consistent differences and ended up pooling males and females together in their research (eg, Barth 1975, Coulson et al 1984, Snell 1991). In the museum skins that we studied, we could not see any consistent differences either. However extensive the variation may be, it is not endless. In the following section, we have tried to point out its limits and to draw the line between NE smithsonianus and European Herring Gulls.
In general, the primary pattern of adult NF smithsonianus is characterized by long and broad grey tongues (clearly ’eating’ into the black markings), rather prominent pale tongue-tips, and usually six primaries marked with black. While each and every marked primary is subtly different from the corresponding one in European Herring Gulls, none of the characters is diagnostic in itself. They should be used in combination, and even then many birds will have to be left unidentified. We will first describe each primary separately, and then explain what combinations can be used. Note that primaries are numbered outwards.

above: American Herring Gull (smithsonianus) adult, St. John's, Newfoundland, Canada, February 24 2008 (Bruce Mactavish). Note the isolated pale spot on underside of P10, a good first pointer.
below: European Herring Gull adult, Katwijk, the Netherlands, November 20 2012 (Mars Muusse). The tongue of
p10 is not visible but in any case cannot be very broad. P5 does not show a complete black band, only a spot
on the outer web (no 'W'-shape). The grey tongue of p8 is shorter than on p7, and lacks a white tongue-tip. There are no 'bayonets' on p7-p8, instead, black on p7-p8 ends rather square and blunt. Note also the rather large amount of black on the inner
and outer webs of p9.

P10 (figure 5, table 1-2, diagram 1)

As mentioned earlier, P10 typically (in 69% of our sample) has a long and broad tongue that is steeply curved at the end. It runs down along more than half of the inner web (best seen from below) and then ends at an angle of almost 90°, leaving a black medial band that is of approximately the same size as the white mirror in many birds (figure 5a). In some birds, the black medial band is even obviously shorter than the mirror. Such a long and almost rectangular tongue was not found in our sample of argenteus but was present in more than 12% of argentatus and 21% of eastern Baltic Herring Gulls. It also occurs in intergrades argenteus >< argentatus. In some NF smithsonianus, the grey tongue is shorter (less than half of the inner web) but often the more or less rectangular shape remains (figure 5b). In a few birds (6%), the grey tongue is very long and joins the white mirror (figure 5d) - creating the so-called ’Thayeri pattern'. In that case, the rectangular shape of the tongue is lost, of course, which may make identification more difficult or even impossible. Even though a ’Thayeri pattern' on P10 is virtually unknown in pure argenteus, it does occur in other European Herring Gulls, especially northern argentatus (Barth 1968; pers obs).
In most argenteus, the grey tongue is short (about 1/3 of the inner web) and wedge-shaped (pointed at the end; figure 5c). This is also true for quite a few birds of other European forms (see percentages below figure 5c). See also diagram 1 for more details.

% NF smithsonianus	65.6	15.3	7.8	5.6
% argenteus	0.0	2.7	95.6	0.0
% argentatus	0.0	0.0	53.1	0.0
% E-Baltic Herring Gull	5.8	1.9	13.5	0.0
FIGURE 5 Variation in pattern of P10 in herring gulls (Peter Adriaens). Percentages refer to the combination of characters illustrated. Here, for instance, it is stated that 65.6% in our sample of NF smithsonianus showed a long (>1/2 of the inner web) pale tongue, which curved very steeply at the end, and that, in addition, all of these birds also showed variable black marks near the tip of the primary (ranging from a very small black spot to a complete black band). This combination is illustrated in figure 5a. As can be seen, only some Eastern Baltic Herring Gulls Larus argentatuscombined the same length and shape of the tongue with black marks near the tip (5.8%) - although not as complete a black band as drawn here. (click on image for larger view)

The pattern of the white mirror is quite variable, and is in itself of little use for identification purposes in our opinion. It may be worth knowing that most NF smithsonianus in our sample had at least a little black between the mirror and the white primary tip, while this was less often the case in European Herring Gulls (table 1). Likewise, a complete subterminal black band is more often seen in NF smithsonianus than in European birds (cf table 2), However, when the pattern of the mirror is combined with the size and shape of the tongue, the characters become more useful. European Herring Gulls with a long, broad tongue on P10 show a tendency towards combining it with a lack of black markings near the tip. In fact, this was the case in all of the argentatus in our sample - though a larger sample might reveal a few exceptions. Of those NF smithsonianus in our sample that showed a long, broad tongue, 94% had variable black subterminal marks. Even birds with a ’Thayeri pattern’ (tongue cutting through to the mirror) seem to retain these marks. Our sample contained 10 birds with a ’Thayeri tongue’ on P10; only one of them had an all-white mirror and tip.
Of the Eastern Baltic Herring Gulls with long, broad tongues, 27% had black subterminal spots, and in German birds (of unknown origin) 38%. One German bird with a ’Thayeri pattern' still retained a small black subterminal spot on the outer web, so this combination is not unique for NF smithsonianus.

Interestingly, a significant proportion (34%) of NF smithsonianus combined a long, broad
tongue (as in figure 5a) with a complete, uninterrupted black band between the white mirror and tip. This combination was not found in our sample of European Herring Gulls (including the German birds), so any bird showing it may well be worth scrutinizing!
By combining all of the above characters (length and shape of tongue with presence or absence of black marks near the tip), the difference between European and NF smithsonianus becomes clearer; this is shown in figure 5: many NF smithsonianus show the combined characters of 5a, while European birds are more like 5c. German birds were not included in the figures, but the combination of all of the above characters on P10 (as in figure 5a) was found in less than 9%. Again, we would like to emphasize that, of these 9% (and of those 5.8% of Eastern Baltic Herring Gulls mentioned under fig 5a), none showed a complete black band between the white mirror and tip.

DIAGRAM 1 Length and shape of the tongue on P10 in herring gulls. 'Thayeri': birds in which the tongue cuts through to the mirror. '>1/2, rectangular': birds in which the tongue covers more than half of the inner web and is steeply curved at the end. '>1/2, oblique': birds in which the tongue covers more than half of the inner web and is rather wedge-shaped. '<1/2, rectangular': birds in which the tongue is short, covering no more than half of the inner web, and is steeply curved at the end. '<1/2, oblique': birds in which the tongue is short, covering no more than half of the inner web, and is rather wedge-shaped. Note especially the difference between NF smithsonianus and argenteus.

P9 (figure 6, table 3)

The grey tongue is again clearly long in most NF smithsonianus (more than half of inner web in over 98% of birds; in 21%, the tongue even cuts through the entire inner web and joins the white mirror). At least part of the tongue is often easily visible from above. In argenteus, fewer birds have a long tongue (>1/2 of the inner web in 59%, with only one bird in our sample showing a tongue that cuts through to the mirror) but in other European forms the length is approximately the same as in NF smithsonianus (see figure 6 for percentages).

Compared with argenteus, the outer web (apart from the white mirror) is less often all-black up to the primary coverts (figure 6c); the base is either entirely grey, or black only reaches the primary coverts in a thin, pointed wedge along the outer edge. Compared with argentatus and Eastern Baltic Herring Gull, the white mirror is usually smaller, more often confined to the inner web (or absent). In these European forms, the white mirror is often also present on the outer web, and regularly interrupts the black outer edge. It is largest in Arctic populations. Note also that in the European forms, presence of a ’Thayeri-pattern’ on P9 (long tongue joining the mirror) often means a large white mirror here too (reaching onto outer web). On the other hand, in quite a few NF smithsonianus the white mirror is still confined to the inner web, while the tongue cuts through (cf figure 1a).

There may already be a certain amount of white on the tongue-tip. If this is the case, the white tongue-tip is usually thin, and shaped like a white crescent, or tip of a fingernail. The amount of white may be more extensive in some; a few birds (5%) even showed an obviously broad white spot, which could be described as rounded or ’pearl-shaped’, and was not found in our sample of argenteus. The above characters are significant when they are used in combination, as can be seen in figure 6a.

CONTINUE: DETAILED PRIMARY DESCRIPTION P8-P4.

East coast birds

East coast: classic birds in P10 -P5 combination

other February adults