This is only a little bit of an exaggeration. Of course, most of us know that gulls have the reputation of being extremely difficult to identify, and that certainly is true, sometimes. But the vast majority of individuals are actually pretty straightforward. Ask any gull expert who has spent hours watching thousands of gulls at a landfill how many he or she couldn’t identify. It will be a handful at best. Every now and then, one comes across a truly puzzling gull that defies identification. Indeed, many “Larophiles” (gull geeks) actively seek such puzzling gulls to tease their minds on cold winter days. But, with practice, most gulls should be readily identifiable.
To begin to get a handle on gull identification, it is perhaps best to consider only the locally common species. Here in South Jersey, we have only four common gull species in winter: Great Black-backed, Herring, Ring-billed, and Bonaparte’s. Each shows a range of plumages – actually, a bewilderingly wide range in all but Bonaparte’s. But if the proper features are considered, most individuals can be quickly identified.
Size: Though each species is variable in size, there is no size overlap between our four winter gulls. And fortunately, these species often flock together. Great Black-backed is the largest by far, being typically fully 30% larger than Herring Gull. Herring, in turn, is twice the size of a Ring-billed, and Ring-billed more than twice the size of a Bonaparte’s. There is, of course, variation in size within most species, with males usually slightly larger than females. Thus a small female Great Black-backed may not dwarf a large male Herring, but there is still a difference! So, if seen together, size will quickly sort out our four local species.
Structure: Using Herring Gull as a standard for reference, Great Black-backed is not only much larger but also has a much heavier chest and heavier bill. Ring-billed looks slimmer than Herring, with a more attenuated shape and a smaller head and bill. Bonaparte’s is very different from all of these, being petite and dove-like with a small head and very slim bill.
Behavior: Behavior is of limited use in gull identification but it does help to predict where each species will be. Great Black-backed Gull is abundant along the coast and offshore but also occurs commonly inland wherever food is available, particularly at landfills and adjacent rivers or lakes. Herring Gull has a similar distribution to Great Black-backed though is more common inland and slightly less common far offshore. Ring-billed Gull is common inland and along the coast but scarce offshore. They are frequently seen in parking lots and at fast-food outlets where they scavenge human leftovers (Laughing Gulls fill this same niche in summer). Bonaparte’s Gulls occur offshore and along the coast, but seldom venture far inland except during migration when they may be seen moving along major river systems or at large reservoirs.
The next level (Molt and aging): Now, back to that bewildering array of plumages… Although you should be able to sort out most of our local gulls without diving too far into plumage details, if you strive to become a certified “Larophile” and sort through flocks of gulls looking for rarities, it is necessary to become familiar with the full range of plumage variation in each species. This requires an understanding of how and when a bird’s feathers are replaced. It takes Herring and Great Black-backed Gulls four or five years to reach adult plumage. Ring-billed takes three years, and Bonaparte’s takes two years. The molt from one plumage to another may happen almost continuously in immature large gulls, and the timing of when each feather is replaced is somewhat variable, accounting for a wide range in appearance between individuals of the same age. In the photos below, I use Herring Gull as an example to illustrate the plumage changes that a typical large gull goes through. Bear in mind, though, that not only is there substantial individual variation, but also there is virtual constant change between one plumage and another so each photo here captures one moment during that cycle. The best way to become accomplished at gull identification is to study your local species and see how they change through the year. Then, when you come across a puzzling individual, at least you’ll have a frame of reference to help rule out one of the common species.
A note about plumage terminology: In order to become fully versed in gull aging, it is necessary to have a vocabulary for naming plumages. One “plumage cycle” (the period during which all feathers are replaced at least once; some feathers replaced twice) of our four common gull species takes place over about a year, beginning some time in spring (earlier in immatures, later in adults) and ending some time the following spring. Because these plumage cycles take place over a one-year period, it is often easiest to refer to a bird in terms of how old it is: “first year”, “second year” and so on, with each year starting and ending around when the bird was hatched. This is referred to as the “life-year system”. In other parts of the world, particularly in tropical regions, other species of gulls (and other families of birds) may take more or less than one year to run through a full plumage cycle. It is therefore, often more informative to refer to a bird in terms of what plumage it is in, i.e., in its “first cycle”, “second cycle”, etc. This is referred to as the Humphrey-Parks system. In this article, for simplicity, I use the life-year system, though both systems are valid.
| Figure 1 – Great Black-backed and Herring Gulls, February, New Jersey. These two species show a bewildering array of plumages prior to reaching their full adult plumage at four or five years of age. Fortunately, no matter what plumage they are in, Great Black-backed Gulls are always much larger than Herring, with heavier bills and heavier chests. Here, two first-year Great Black-backs (the giant birds at left and back) are accompanied by a second year (brown bird at center), adult (right), and third-year Herring Gulls. |  |
| Figure 2 – Great Black-backed (left) and Herring Gulls, December, Delaware. Even in silhouette, it is easy to see that a Great Black-backed has a much heavier chest and bill than a Herring Gull. |  |
| Figure 3 – Adult Herring (back) and Ring-billed Gulls, December, New Jersey. Adults of both species are gray and white with black-and-white wing-tip markings and (in winter) brown head streaking. Many adult Herring Gulls show some black on the bill and may show a ring similar to a Ring-billed Gull’s. Size is the most obvious difference but also notice Ring-bill’s more delicate proportions with smaller head and bill and slimmer body. Leg color differs on adults of these two species but not on younger birds. |  |
| Figure 4 – Adult Ring-billed Gull (front) and first year Bonaparte’s Gull, February, New Jersey. Not only is Bonaparte’s less than half the size of a Ring-billed but also notice its more dove-like proportions with smaller head and much slimmer bill. |  |
| Figure 5 – Juvenile Herring Gull, August, North Carolina. Herring Gull is an excellent subject to study to learn about gull aging. Juveniles are brown overall with crisply patterned wings and back and mostly blackish bills. Note especially the small, dark-centered, pale-fringed scapulars and pointed primaries. |  |
| Figure 6 – First-year Herring Gull, December, New Jersey. By mid-winter, most birds have replaced the juvenal scapulars with larger, paler feathers with variable dark bars. The wings, though more worn, still show neatly checkered wing coverts and pointed primaries. The bill often begins to show some pale at the base (occasionally extensive). |  |
| Figure 7 – Second-year Herring Gull, December, Maryland. Second-year birds often still look mostly brown but usually begin to show some pale gray on the back, a paler-based bill, and a paler brown eye. Note especially the more irregular markings on the wing coverts and slightly blunter-tipped primaries than first-year birds. |  |
| Figure 8 – Third-year Herring Gull, December, New Jersey. Third-year birds take on a much more adult-like appearance with extensively gray upperparts, extensively white underparts, pale eye, and mostly pale bill. Note especially the black primaries with small white tips. This plumage is highly variable, and some individuals may show a full dark tail-band whereas others show a fully white tail. The patterning on the primaries is always the safest distinction from second-year birds. |  |
| Figure 9 – Adult Herring Gull, December, New Jersey. After four years, most individuals attain the familiar gray-and-white adult plumage. Some fourth-year birds may retain a few signs of immaturity such as a few brown markings on the wings or dark markings on the tail. Photos by Michael O’Brien. |
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