American Herring Gull (smithsonianus)
(last update: October 30, 2015)
American Herring Gull (smithsonianus) adult.
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).
|
||||
| % NF smithsonianus | 55.3 |
23.5 |
11.4 |
9.8 |
| % argenteus | 9.8 |
8.4 |
67.9 |
13.9 |
| % argentatus | 8.6 |
45.7 |
5.7 |
2.7 |
| % E-Baltic Herring Gull | 1.4 |
62.7 |
2.9 |
1.2 |
FIGURE 6 Variation in pattern of P9 in herring gulls (Peter Adriaens). Percentages refer to the combination of characters illustrated. Here, for instance, it is stated that 55.3% in our sample of NF smithsonianus combined a small white mirror (concentrated on the inner web) with a restricted black pattern on the outer web (not reaching primary coverts, and a rather long grey tongue on the inner web (>1/2), as illustrated in figure 6a. Paleness of the tongue-tip was not included in the 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).
| TABLE 3 Extent of white mirror on P9 | |
| P9 | % of birds with mirror
present also on outer web |
| NF smithsonianus | 24 |
| argenteus | 36 |
| argentatus | 78 |
| Eastern Baltic Herring Gull | 93 |
Note: Jonsson & Mactavish (2001) found 44% with
mirror on outer web in their sample of NF smithsonianus; however, in 26% of those, the amount of white on
the outer web was very small. Barth (1968) recorded an
average similar to ours in argentatus, namely 71%; Mierauskas Br Greimas (1992) obtained a lower value |
|
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.