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Understanding gulls
To make sense of immature gulls, ignore how pale or dark the birds look
Contributed by David Allen Sibley
Published: April 20, 2012  THE SAME BUT DIFFERENT: Wing coverts, wingtips, and head and body feathers on the gulls above differ dramatically in color, but each bird is a Herring Gull about a year old.
Art by David Allen Sibley
Click to enlarge
In any flock of immature gulls at this time of year, the many colors and patterns can be confusing, but a couple of things will help you sort through the variety. First of all, every gull in June and July will be near its “birthday,” so the birds don’t vary much in age, only in appearance. Unlike humans, who have birthdays throughout the year, all gulls fledge in the month of July. This fact puts limits on the variation you see.
My illustrations above show two birds. One is very pale. Its wing feathers are strongly bleached (pale wingtips and nearly white wing coverts), and the feathers on its head and body are pale. The other bird is the same age, but its wing feathers have resisted bleaching (its wingtips are dark) and its body feathers are dark and blotchy. Both are Herring Gulls about a year old. What you’re seeing is just individual variation. As far as we know, the two birds could have come from the same nest.
For the most part, you should ignore how pale or dark the birds look overall and focus instead on characteristics such as size and shape or the pattern on the wings and tail. The range of variation is different for each species, but you can be sure that the wingtips of any individual gull in June will be paler than they were the previous winter, not darker.
In all species of gull, there is a gradual progression from browner immature birds to grayer and cleaner adults. Ring-billed, Laughing, and other smaller gulls make that transition quickly; they look a lot like adults, with clean gray backs and whitish underparts, by their first birthday. This means that any gull that looks brown in June is one of the larger species — Herring, Western, California, and others. Depending on your location, that fact alone can come close to identifying the species.
All-brownish plumage by itself won’t identify a gull, but it goes a long way toward culling the list of possibilities.
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David Allen Sibley is the author of The Sibley Guide to Trees, The
Sibley Guide to Birds, Sibley’s Birding Basics, and Sibley guides to
birds of eastern and western North America.
Read more by David Allen Sibley.
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