American Herring Gull (smithsonianus)

(last update: October 30, 2015)

Amar Ayyash (US)
Bruce Mactavish (Canada)
Dave Brown (Canada)
Mars Muusse (Netherlands)

American Herring Gull (smithsonianus) adult.

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
% argenteus
% argentatus
% E-Baltic Herring Gull
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 argentatus combined 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.

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.

TABLE 1 Extent of white mirror on P10

% of birds with all-white mirror + tip
NF smithsonianus
Eastern Baltic Herring Gull

Note: Jonsson & Mactavish (2001) came to almost the same result in NF smithsonianus, namely 7%. Barth (1968) found a similar average percentage for argentatus, namely 54%, while in Eastern Baltic Herring Gulls, Mierauskas & Greimas (1992) found an average of 32.5% (on birds from Latvia and Russia), and Kilpi &
Hario (1986) recorded a total of 46% (on birds from Finland). Olsen & Larsson (2003) give 53% for argentatus and c 20% for argenteus. Coulson et al (1984) examined many argenteus (n = 1484) from various breeding colonies in Britain, and noted the following percentages: 30.9% in Shetland birds, 20.5-25% on the British east coast, 9.3-10.8% on the British west coast, 13.4% in North Wales, and 1.4% in Lancashire,
England. They concluded that European Herring Gulls breeding on the west side of Britain show on average more black near the tip of P10.


TABLE 2 Amount of black between white mirror and tip of P10
% of birds with uninterrupted subterminal black band
NF smithsonianus
Eastern Baltic Herring Gull
Note: Jonsson & Mactavish (2001) recorded only 39% in NF smithsonianus but, in another 24% of their sample, the subterminal black band was still quite thick, and was only or mostly interrupted at the shaft.
Barth (1968) noted an average of 8.4% in Norwegian argentatus. Mierauskas & Greimas (1992) found an average of 15% in eastern Baltic Herring Gulls.

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.