Mendo Gulls, Part 4. November - February

This is the fourth in a series of gull identification and ageing along the Mendocino coast. See the May 2025 Issue of the Oystercatcher for an introduction to this series and coverage of gulls along the Mendocino coast during March-June, and the July and October issues for coverage of Western, California, Heermann’s, Ring-billed, and Glaucous-winged Gulls in summer and fall. In the figures below we will cover Western and California gulls in winter plumages, along with our three next-most common wintering species, American Herring, Short-billed, and Iceland (Thayer’s) Gulls. We’ll have one more finale, for hybrids and rarities in winter. As in previous installments, all photos were taken along the central California coast (SF-Mendocino), for this installment in October through early March.

Figure 1. Non-adult Western Gulls (WEGUs) and California Gulls (CAGUs) in October-February.

Again, adults are not shown because they vary little from how they look at other times of the year. Recall adult WEGU is our only gull that does not get dusky head mottling in winter, while in adult CAGUs, moderate dusky mottling changes to white and their legs and bills become bright yellow by spring.

The only real change in younger plumages through the winter is that new “formative” back feathers grow in. In WEGU note that the new feathers of 1st-winter birds (A, 4 Jan) are dusky or blackish but not reaching the pure dark gray color of adults yet, whereas in 2nd-winter birds (B, 5 Nov), the new feathers are adult-like. Note also the muddy pinkish base to the bill and less-checkered wing coverts of the 2nd-winter bird. Third-winter WEGUs (C, 4 Dec) become quite adult-like except for dark in the bill and tail, the latter barely visible here but shows up as a thin black band or dark spots when flying.

First-winter CAGUs continue to vary from paler (D, 27 Feb) to darker (E, lower left) and the new feathers come in with dark centers at first but by later in winter can be more adult-like. These formative feathers are replaced from August to January and, interestingly (to put a positive spin on it), they are more juvenile-like when grown in fall but more adult-like when grown in late winter. Individual variation in replacement rates thus adds to the variability in overall 1st-winter and 2nd-winter plumages, in all Larus species. The photo of flying birds (E, 16 Oct) also shows two 2nd-winter birds (top left and bottom right) and an adult (center). Note the upperwing surface to the 2nd-winter bird at lower right, with broader and blacker outer primaries than in 1st-winter birds and inner primaries that are more adult-like.

Third-winter CAGUs (F, 7 Dec) tend to have darker head mottling than adults throughout the winter, and note also the slightly browner wing coverts and dark ring around the bill tip, both not quite adult-like. In all cases compare the bill patterns in these images for a good way to tell WEGUs from CAGUs; most 2nd-winter WEGUs have darker and “muddier” bases than the bird in B, and 3rd-winter and adult WEGUs do not have the distinct extra black spot of 3rd-winter and adult CAGUs. And don’t forget back color, always darker in WEGU than CAGU, and leg color - always pink in WEGU but changing from paler pink, to pale greenish or bluish, to brighter yellow among these ages in CAGU.

Figure 2. American Herring Gulls (AHGUs) in October-February

First of all, note that this species was recently split from herring gulls of Eurasia, which results in AHGU rather than HERG (and, now, Heermann’s Gull becomes HEGU, the way the ball bounces in coding rules-- we’ll get used to it).

First-winter AHGUs are one of our more difficult IDs because they can vary so much, especially in bill color, and their eyes have not yet become staring pale as in older birds (see above).

Darker birds with blackish bills, especially in fall (A, 29 Oct), can be confused with 1st-winter WEGUs but note the smaller and slimmer bill that is just starting to become tinged pink at the base; in WEGUs the much stouter bill stays fully black for the first full year. Many AHGUs look like the bird in B (paler and with some pink at the bill base) while others can become quite frosty by late winter (C, 27 Feb). Bill and head shape differ between the sexes in all gulls, and the birds in B (male, with larger bill and wedge-shaped head) and A and C (females with smaller bill and rounder head) are classic examples, making it look easier than it is in general, as there is some overlap.

A key difference in 1st-winter AHGUs from our other species is that, in flight, the inner four primaries are paler than the others, resulting in a pale “window” or “panel” here. This is shown to varying degrees in D (29 Oct) and E (27 Nov). Note the feathers themselves are pale with dark shaft-streaks and tips forming what is often called an “anchor pattern” in birds. Some 1st-winter AHGUs can get even brighter pink bill bases than on these, and can be confused with 1st-winter CAGUs. But, besides the pale inner-wing panel, note also that leg color is a darker or more bubblegum-ish pink in AHGU than in first-winter CAGU (and stays pink while CAGU leg color changes), and the wing coverts are more evenly patterned in AHGU (compare with the CAGU in Fig. 1D).

Plumage variation with age in AHGU is similar to that of WEGU and CAGU. Second-winter birds (F, 7 Oct, Tim Bray) look more like 1st-winters than adults, being largely brownish and usually sporting bright pink bills with dark tips. They differ from 1st-winter birds in having more adult-like black and pale gray to the primaries and they start to get that charateristic paler eye of adults. Second/3rd-winter (G, 29 Oct, probably a slow-maturing 3rd-winter, possibly a fast-maturing 2nd-winter), and 3rd-winter AHGUs (H, 23 Oct, and I, 6 Jan) become more adult like but with some dusky markings to the upper wing coverts, tail, and bill. The “staring” pale eye of adults can become fully developed (as in H) or almost so (as in G and I).

Note in I the extent of white to the wing tips, more than typical of WEGU and CAGU, with the white “mirror” of the outer primary often larger than this, as it also averages larger in adults than in 3rd-winter birds. Finally, adults (J, 9 Oct) are easy to pull out of standing gull flocks due to their much paler backs than our other species, and those staring pale eyes. Legs remain bubblegum pink and the bill of adults can be similar to that of adult WEGU in pattern, except being slimmer and being a bit more yellow or even slightly greenish yellow, less school-bus yellow that in WEGU (but not as greenish as in adult THGU, below)

Figure 3. Short-billed Gulls (SBIGs) in October-February

As in the herring gulls but opposite to the Iceland Gulls (below), SBIG was recently split from Eurasian taxa, which were already called Common Gulls. Why the name of our bird was changed from the familiar “Mew Gull” has a lot of us puzzled and/or irked, as not only do we lose a familiar name, but the nice and easy MEGU has to become the less palatable SBIG because SBGU now conflicts with the code of Slaty-backed, now the even more cringe-worthy SBAG. Oh well.

Whatever we call it, we are lucky that it is the smallest of our Larus gulls, with a dainty bill and pigeon-like rounded head, making ID rather straightforward in all of its plumages during winter. Because it is so readily identified, we don’t typically notice how variable first-winter birds are, from very dark like WEGU, especially in fall (A, 14 Oct), to more typically pretty dark (B, 7 Dec, and C, 26 Nov), to frosty pale, especially by early spring (D, 2 Mar). Note the wing coverts are dusky-olive when fresh with a paler panel to the larger greater coverts. The tail pattern in SBIGs (E, 7 Dec) can vary from appearing all black (as in 1st-winter CAGU) to having a tail-band effect (as in 1st-winter Ring-billed Gull, RBGU) but, in any case, size, head shape, and the dainty bill can be turned to for ID from these. Note by early spring (D), adult-like back feathers can molt in on 1st-winter birds.

Second-winter and 3rd-winter birds follow your familiar (by now) plumage progression, despite this species being smaller than the other species and, you might think, quicker to mature. It actually takes more time to reach adult plumage than the slightly larger RBGU. Second-winter birds (F, 4 Nov, Lisa Walker) have more gray in the back but at least some brown and fringed wing coverts, and 3rd-winter birds (G, 26 Nov and H, 29 Oct) are adult-like but with a variable amount of brown wash and dark markings to the wing coverts, and black in the tail varying from a band (G) to a few dark spots (H).

Adult SBIGs (I, 26 Nov) have comparably heavy dusky mottling to the heads through winter. The white in the wing tips is relatively extensive, between that of AHGU (above) and THGU (below); note also the white “tongues” between the gray and the black on primaries p5-p8. Bill color in SBIG becomes pale at the base but is typically washed dusky or duller than in other species, becoming olive by the 2nd winter and is unmarked greenish-yellow in winter adults, with no distinct red or black spots, although it can gain some smudginess from summer coloration. Leg color changes from pale pinkish to dull yellow from 1st to 3rd winter birds and, like in CAGU, both bill and leg color become brighter yellow in spring, typically after they leave our area.

Figure 4. Iceland (Thayer’s) Gulls (THGUs) in October-February

In contrast to the recent splitting of the previous two species, THGU was lumped with the white-winged Iceland Gull (ICGU) that breeds in (where?) Greenland actually (it winters in Iceland), along with an intermediate population breeding in eastern Nunavut, referred to as Kumlien’s Gull (KUGU); they are all called Iceland Gulls now, but we keep the familar name and code THGU for our birds. THGUs breed in the Northwestern Territories and have the darkest wing tips of the bunch, a reason that, until relatively recently (1973), it had been lumped with AHGU!

So depending on where ICGUs breed, the wing tips of adults can be pure white (ICGU), white with some gray markings (KUGU), or nearly black (THGU). First-winter birds also follow this pattern but will have some dark markings compared with adults, which contrast with background color more in ICGU than in THGU. In any case, because of this we see a lot of variation in the upperparts and wing tips in 1st-winter THGUs, from brownish and blackish, respectively (A, 9 Nov), to frostier and blacker (B, 14 Dec), to quite frosty and grayish (C, 6 Jan), to very pale gray in both (E, possibly a KUGU or intergrade between THGU and KUGU). In all cases note the rounded heads and smaller bills than in AHGUs, not quite half way in the direction of SBGU. In flight (D, 27 Jan), 1st-winter THGUs can resemble GWGUs but have smaller bills, and the wing tips are paler looking than in flying 1st-winter AHGUs.

Again, 2nd-cycle birds (F, 6 Jan) have juvenile-like wing coverts but more adult-like gray in the back and 3rd-winter birds (G, 3 Dec, H, 15 Nov, and I, 23 Dec) are adult-like with dark markings in the upperwing and tail (the birds in H and I may actually be in their 4th winter). In adults (K, 6 Dec) note that the bills have a greenish tinge, a very useful tip for ID’ing these. Another key difference from AHGU is that the eye color is darker by age, usually dark until adulthood and then varying from darkish to palish (as in K) but never staring as in AHGU. The wing tips have more white than any of our other species in adults, typically showing more than in the 4th-winter bird in J, and frequently showing the entire tip white, without a dusky tip.