Mendo Gulls, Part 1: March - June

Gulls. Just the word is enough to cause birders to run in terror to the nearest trees to separate chickadees from Acorn Woodpeckers. And there is good reason. I once counted up the number of “identifiable plumages” as related to age and seasonal molt status and came up with no fewer than 90 plumages among the nine regular gull species that occur in central California. Then you add in individual variation, effects of variable solar exposure, molt, rare species, and (gasp!) hybrid combinations, and you might as well take up quantum field theory. I’ve been looking at gulls in the Bay Area for over 45 years and have taught many gull classes for the Marine Sanctuaries Beach Watch program, from Half Moon Bay to Gualala, and I still run into those that I can’t identify (not infrequently), and in some cases with little or no clue. But there is some hope if you are willing to give it some effort and time.

In this series I will share what I’ve learned about identifying and ageing gulls along the Mendocino coast. I’ve been studying them in the Fort Bragg area now for a year, and while I still don’t have their movement patterns and roosting sites figured out (we’ll cover this more this coming fall and winter), the same ID criteria I have learned in the Bay Area apply. Unless indicated, I’ll use my own photographs taken here and in San Francisco (largely at Ocean Beach) to illustrate seasonal changes and age determination. We’ll start with species we see regularly in spring and summer, and then we’ll branch out into other species in fall and winter as they arrive from northern breeding grounds.

Start with your common year-round species: Western Gull (WEGU)

When it comes to gulls we are relatively lucky in that WEGUs are easy to identify based on structure and plumage. It is the darkest gull that we have in all plumages, and the largest one with the largest bill on average. My advice to gull beginners is to go out throughout the year and spend some time with WEGUs. See how variable their sizes and bill shapes are. We will start with adults (Figure 1). Then apply these structural differences to identify WEGUs of younger ages (Figure 2). Learn how WEGU plumages change with age and season. In the figures below we will also cover California Gull (CAGU), which is the other regular gray and white gull here throughout spring and summer, and we’ll touch on “bleached” first-cycle gulls of other species that occasionally over-summer on our coast.

Molt cycles are commonly used to age gulls. 1st-cycle gulls refer to those from fledging to the first complete molt at about a year of age. During this molt and for the following year we have 2nd-cycle gulls, followed by 3rd-cycle gulls, and we will also make passing reference to 4th-cycle gulls, those between 4 and 5 years old. Once plumage has fully matured and does not change from year to year (“definitive appearance” or birds within the definitive molt cycle) we will call them “adults,” even though this term refers more to reproductive than to plumage maturity. Within each cycle there can be 2-3 plumages based on partial molts but to make things easier (hah!) we will not worry about these too much, as individual and wear-related variation through the cycle tends to obscure that based on inserted partial molts.

Figure 1

Figure 1: Learn Your Western Gulls and start with the adults (A, 26 April). Their backs are dark and bills are orange-yellow in spring, with a red spot on the lower mandible that can be hard to see. Notice the large bill size and stout shape, which vary a bit by sex (the front adult looks like a female compared with males behind her). In flight (B, 7 May, photo by Cedric von Briel), adults have relatively extensive black wing tips but a smaller white “mirror” on the outer primary than our other adult gulls. Third-cycle gulls (C-D, 1 March and 19 April) are like adults but have some brown in the wings, black in the tail, and a bill that can change from dusky and yellow in fall and winter to yellow with a black tip in spring. Note the large bill in bird D, typical of a male WEGU.

Figure 2

Figure 2 (right): Second-cycle Western Gulls differ from third-cycle birds in having brown wings like first-cycle birds but some gray on the back (A, 30 April; B, 30 March). By spring they typically acquire adult-like back feathers and scattered wing coverts. Beware, however, that some fast-maturing 2nd-cycle birds can overlap with slow-maturing 3rd-cycle birds, and there can be even more overlap between 3rd and 4th cycle birds, the latter indistinguishable from adults in most cases. Note the broad wings in B, a good mark to distinguish these from California Gulls. First-cycle birds (C, 13 Mar; D, 22 April) are dark brown but can bleach by spring to paler brown. Note also the especially large and entirely black bills through the 1st cycle in WEGUs, one of the best way to tell these from 1st-cycle CAGUs.

Figure 3

Figure 3 (below): California Gulls are the other black-and-white gull commonly seen along the Mendocino coast in summer, even though they don’t breed very close. Adults (A, 2 March) have slightly paler backs than WEGUs, yellow legs and feet (much brighter in spring than fall and winter), and a slender bill with both a red and a black spot on the lower mandible. These are usually gone by May. Younger birds are more common in spring and summer, such as the third-cycle bird in B (7 May, Lisa Walker) and the second-cycle bird in C (23 May).

Note the mostly gray wings in the 3rd-cycle bird and the mostly brown wings in the 2nd-cycle bird, similar to the patterns in WEGUs. First-cycle birds are variable (of course!), but many, such as the bird in D (4 June), get bleached wing coverts by spring and summer. We’ll explore why this occurs in some CAGUs in a later installment. Others do not get as bleached, such as the bird in E (22 April). Note especially in 1st-cycle CAGUs the pale based bill with a clean dark tip, the key feature in separating these from 1st-cycle WEGUs, and the proportionally longer wings in flight. Practice looking at wing shapes in flying WEGUs and CAGUs as they are readily distinguished this way with practice. Note that the leg color is pale pink in 1st-cycle CAGUs, after which it turns to yellowish-pink and can be greenish or even bluish in the 2nd and 3rd cycles, a unique leg color for gulls.

Figure 4

Figure 4 (above): First-cycle birds of a few other gull species can grace our shores in spring and summer, those that decided not to make the northward trek to the breeding grounds. Glaucous-winged Gulls (A, 22 April; and B, 20 April) are the most common of these. In shape and size (of both body and bill) they are identical to WEGU but can vary a bit more in size, some female GWGUs being smaller. The pale wing tips as compared to WEGU is a key feature and they are also paler overall. Bill color also tracks that of WEGU, being black through the first cycle.

Rarer but still rather regular in California through May are Glaucous Gulls (C, 25 March). These are even whiter than GWGUs and differ primarily in the bright pink base to the bill through the 1st and 2nd (in this case) cycles. Finally, we occasionally have some bleached American Herring Gulls stay for the summer, such as this bird (D) that spent last summer along the Mackerricher State Park beaches. Note the small bill, and a bill-color pattern that is unlike that of 1st-cycle CAGU. I often wonder if these very bleached 1st-cycle gulls (of CAGU, GWGU, and AHGU) had spent the previous winter basking somewhere on a sunny Baja California beach.