BIRDING BY HINDSIGHT: A Second Look at Gulls

Gull identification. The very phrase itself strikes terror in the minds of many birders. Especially those dreaded immatures – immature gulls, that is, not birders. I know several skilled and knowledgeable birders who aren't afraid to identify a silent Empidonax or the most nondescript fall warbler, but when it comes to gulls they literally look the other way.

But if it's any consolation, this piece has no intention of discussing the intricacies of the more challenging gull identification problems: e.g., Herring vs. Thayer's vs. Iceland vs. Glaucous; or picking out an immature California or Lesser Black-backed in a flock of Herrings and Ring-billeds; or how to tell if that presumed Great Black-backed might actually be a Slaty-backed or Western. Each of those would be separate articles in their own right.

Instead, what follows is an introduction to some of the things to look for –and look out for – when identifying gulls. There are certain features on gulls worth taking a second look at, features that when not taken into account could easily lead to misidentifications. Also included here are a few brief notes on identification problems involving some specific gulls.


Probably the first step in identifying any species of gull is to simply be aware of its age and corresponding field marks. Some field marks might be diagnostic on a gull in full adult plumage, while attention to these same characters on an immature might lead to a misidentification.

For example, you may know that a brown eye would be a good thing to look for when trying to find a Thayer's or California Gull, but you also need to be aware that some third-winter Herring Gulls (which resemble full adults) might also have brown eyes. Other common misidentification problems (e.g., involving bill color and wing tip pattern) resulting from observers not being aware of a gull's age are mentioned below.

Certainly, there is no room here for a discussion on how to age gulls; nor was there apparently any room in the Peterson or Robbins field guides to show gull plumages at all ages. If you rely on either of these guides when identifying gulls, you will not get very far. The Geographic field guide is a far better choice, and for even better information I highly recommend the second edition of Gulls: A Guide to Identification by Peter Grant. [Author's Note, August 2010 – Since 1995, there have been several other books, field guides, and journal articles on gulls.]


Simply stated, gulls go from one plumage to another by molt: old feathers are lost and new ones grow in, generally in the fall and spring. But it is important to realize that the molting process may last for several weeks, so that a gull's plumage may appear atypical, even in disarray, and relatively difficult to figure out for weeks at a time. Note as well that not all individuals of the same species begin or end their molts at the same time, and they may not progress at the same rate. Therefore, it is not unusual to see two individuals of the same species and same age sitting side-by-side and looking quite different. Also, as gulls molt, bill and eye and leg colors may be changing as well – but again, not necessarily at the same rate.

Consider again, then, a Herring Gull in third-winter plumage as mentioned earlier. Not only could one have either a yellow or brown iris, but also its bill might have some black on it, or some red, or both colors. Its wing tips may show one white spot or "mirror" within its black wing tips, while another third-winter Herring might have two, and still another may show none. And while its tail may show a solid black tail band, on the other hand it might possibly have only a paler and broken one.

Other examples of gulls in molt being frequent sources of identification difficulties are mentioned below; these typically tend to involve confusing and atypical wing tip patterns.

Size and Shape

Certainly, size differences between some gull species are important considerations in the identification process. Typical Glaucous Gulls look larger than Icelands, Thayer's also average larger than Icelands, Great Black-backeds should appear larger than any other "black-backed" gull, Herrings are normally larger than Californias and Lesser Black-backeds and most Thayer's – the examples are many. Unfortunately, relative size is far trickier to deal with than most birders realize.

For one thing, males of a given species are often noticeably larger than females. Therefore, it is entirely normal for a male Iceland to look as large as a female Thayer's, or for a male Thayer's to appear as large as a female Herring. More than once I have seen Great Black-backeds and Glaucous Gulls – presumably females – look essentially the same size overall as Herring Gulls. When trying to judge a gull's size, by the way, it is often more useful to consider only parts of its body – e.g., bill size, neck thickness, wing span, etc. – rather than its overall length or height.

Similarly, head shape is an equally elusive concept, with apparent differences often a function of the gull's sex rather than its species. So while those "larger" species tend to have flatter forehead profiles than their "smaller" and rounder-headed counterparts, a Thayer's Gull, for example, could either look like a flat-headed Herring or a round-headed Iceland.

There is also the relatively unknown but potentially serious problem of what has been termed size-illusion. You may not believe this until you try it, but if you have identically sized objects (or gulls) in view through optics (or telephoto lens) at the same time, and one is a few feet farther away, it can appear larger – not smaller – than the closer one! This illusion is more evident at relatively close range and with higher magnifications. It may be difficult to explain, but size-illusion is a reality and it should therefore be obvious that size comparisons involving gulls or any other birds should only be made if the birds are side-by-side, and exactly the same distance away.

On a similar note, direct size comparisons should also only be made on birds exactly perpendicular to your line of sight. If at an angle, a gull's body and bill lengths are foreshortened, appearing smaller than they actually are.

Eye Color

The identification of some gulls often relies on iris coloration, but here again there are some pitfalls to be aware of. First of all, a pale iris will look dark at a distance or in poor light, so when searching for dark-eyed species like Thayer's or California (or even Mew) gulls make sure you are close enough to accurately determine that the iris is dark. The easiest way to do this is to examine any adjacent gulls known to be yellow-eyed (e.g., adult Herring or Ring-billed): if you can see their yellow eyes, then you know you really could see the dark eyes on that gull you're looking for.

The second step is to make sure that gull with the dark iris is in full adult plumage. As mentioned earlier, a third-winter Herring Gull, which generally resembles an adult, might have a dark eye. It would then be easy to assume it to be an adult gull and misidentify it as a Thayer's or California on the basis of iris color. I also suspect some fourth-winter gulls, which really are essentially in adult plumage, might still have a dark iris: two documented Great Black-backed Gull records of dark-eyed adults probably involved fourth-winter birds (see The Loon 64:12-15 and 65:50-51).

Bill Color

The pattern of colors on a gull's bill is another important feature to consider when identifying some species. As indicated earlier, however, bill color patterns change with age, and, unless the observer is aware of a gull's age and the range of variation possible during that age, misidentifications will result.

Consider the Herring Gull, for example. First-winter birds normally have an all-dark bill; second-winter birds typically have a two-toned bill with a pale base and black tip; as mentioned earlier, bills on third-winter Herrings are variable in pattern but often show a black ring near the tip; and fourth-winter/adult Herrings should have an all-yellow bill with a red spot near the tip of the lower mandible.

One problem, though, is that a first-winter Herring may already have acquired the two-toned bill associated with second-winter birds. An unwary observer could then easily mistake it for a first-winter California Gull based on the bill pattern, especially if that Herring Gull were a small female. Novice gull watchers unfamiliar with the bill patterns of sub-adults also have trouble with those third-winter Herrings with a ringed bill: these get misidentified all the time as Ring-billed Gulls when nothing other than bill pattern is considered. (By the way, it is entirely normal for other third-winter gulls –e.g., Iceland, Glaucous, Thayer's, California and Great Black-backed – to have ringed bills as well.)

And fourth-winter Herrings often show both black and red spots on the lower mandible (i.e., traces of the black ring from third-winter still present along with the red spot of an adult), so that an identification based primarily on bill pattern could easily result in an erroneous report of an adult California Gull.

Gray Areas

To some birders, the entire issue of gull identification is just one big "gray area" we would be better off without, but that's not the point of this paragraph. Gray areas here mean the shades of gray (or black) on an adult gull's back and upper wing surfaces that often serve to separate one species from another. Mew and California gulls are darker than Ring-billeds and Herrings, Great Black-backeds are darker than Lessers, Bonaparte's are slightly darker than Black-headed Gulls, etc.

The problem is that shades of gray are highly dependent on light conditions and the angle at which the gull is from the observer. Judging gray and black shades in photographs is even trickier: a camera's settings, any computer editing of digital photos, and a published page's printing process must be taken into account (along with film type and developing variables with older photos). It is not unusual, then, to see an adult gull appearing darker than another adult of the same species, and it is risky to identify, say, a suspected California Gull among some Herrings and Ring-billeds based primarily on a darker back and wings.

Wear, Fading, Albinism, Hybridization

As difficult as it is just to identify gulls within their normal range of plumage variations, there will be times when faced with one of abnormal appearance. A gull's plumage, especially in spring and summer, can look quite bedraggled or worn after months of exposure to the elements; similarly, it may also appear unusually pale or faded. Such gulls must be identified with caution, with the main problem in Minnesota being faded immature Herring Gulls frequently mistaken for Thayer's.

Albino gulls, though rarely seen, do exist and would be another source of confusion; obviously, it would not be hard to mistake one for a Glaucous or Iceland or perhaps even an Ivory Gull. And a more likely possibility would be to encounter a hybrid gull, and imagine the potential there for a misidentification!

More Gulls with an Identity Crisis

Some of the most frequent gull misidentification problems in Minnesota have already been pointed out:

• Brown-eyed Herring Gulls might easily be miscalled adult Thayer's.

• A first-winter Herring Gull might have a two-toned bill and thus be mistaken for a first-winter California.

• Beginners frequently misidentify third-winter Herrings and other gulls with ringed bills as Ring-billeds.

• Many fourth-winter Herrings have both a black and red spot on the bill and could easily be misidentified as adult Californias.

• Some Thayer's Gull records turn out to be sightings of faded immature Herrings.

Wouldn't it be nice now if readers could avoid such difficulties from now on? It would be even nicer if this list ended at five. Unfortunately, there are a few other gull identification problems that birders should especially be aware of:

• One of the most common of all mistakes involving gulls occurs in late summer and early fall when adult Ring-billed and Herring gulls are in molt. At this time the black tips on their outer primaries are still growing in and are more difficult to see. Therefore, when viewed briefly, at a distance, or at a difficult angle, these gulls are erroneously reported as Thayer's or Glaucous or Iceland.

• Franklin's Gulls are another frequent source of confusion, with first-summer and second-summer birds (i.e., one-year-olds and two-year olds) being mistaken all the time for adult Laughing Gulls. The problem is that such Franklin's Gulls may have nearly complete black hoods, but at the same time they may not have yet developed the white area between their black wing tips and the rest of the wing. It is easy to see how easy it is to miscall such birds adult Laughings.

A less frequent problem with Franklin's Gulls is similar to the one described above involving molting adult Herrings and Ring-billeds. Adult Franklin's in molt during spring and summer may show little or no black on the tips of their outer primaries; as a result their wing tips may appear white, and, combined with the white trailing edges of their wings, this creates a pattern quite similar to an adult Little Gull.

• Finally, the casual Black-legged Kittiwake has been involved in misidentifications with at least four species that I am aware of. First, second-winter Ring-billed Gulls, which mostly resemble full adults, typically lack any white mirrors in the black wing tips: a "dipped-in-ink" pattern is the result, and a beginner might then misidentify it as a kittiwake.

Second, note that a Bonaparte's Gull in juvenile plumage, which is not illustrated in any field guide, has a distinct dusky smudge on its hindneck; therefore, it is easily mistaken for a first-winter kittiwake (whose hind-neck marking is darker).

The third and fourth kittiwake look-alikes don't occur often enough here to present that much of a problem. But note that a Sabine's Gull's wing pattern, while striking, is not quite as diagnostic as most would think, since a first-winter kittiwake also has similar black and white triangles on its wings (the difference is in the kittiwake's black bar on the gray upper wing coverts). And lastly, note that a first-winter Black-headed Gull is not the only small gull with a black-tipped yellow bill; the field guides fail to mention that first-summer kittiwakes have a similarly patterned bill.

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Now that late fall is here, good gull watching times are upon us. Plenty of migrants are passing through and arriving for the winter, rarities often turn up now, and most species at this time of year tend to be in plumages less likely to be subject to molt and other complications. Just keep in mind that none of the field guides – Geographic included – have all the answers, and it's always a good idea to base your identifications on a combination of field marks, not just one feature that might be variable enough to lead you astray.