Now that I am able to actually look at the Infamous Gull Chart (thank you Treesa), I will officially weigh in…
First, the blasphemy: Gull ID is not nearly as important as some folks might want us all to believe. Depending on where one is standing at a particular instant in time, the majority of gulls one would be looking at will be one of maybe three or four species (plus or minus hybrids). In a census, we shoot for 95%. Most of us don't need to be able to identify every possible gull. Missing the Slaty-backed Gull DOES NOT MATTER. Most folks interested in seeing a Slaty-backed or Black-headed Gull would do better waiting for someone else to find it, given that the alternative is sorting through gulls for hours on end over years and years.
There will always be gulls in a group that we cannot identify, no matter how many gulls we’ve looked at over the years. The pretense that we can identify every gull is just that, pretense. The real Zen in gull ID is recognizing, first, that we cannot satisfactorily place a name tag on every gull and, second, it does not matter whether we place a name tag on every gull. What matters in birding is the answer to the question: are we having fun, yet?
So, the gull chart – It IS useful, though the point made by Mr. Irons about the importance of wing-tips is well taken. There is method in starting with adults, in part because they are usually better illustrated and easier to sort than juveniles. Because structure holds from adults to juveniles, if one can get comfortable with adults, the step into the more complex sub-adult morass can be more easily taken.
The chart could use some qualifiers, the most important being: how do we know we are looking at an adult? I’m also not sure about the efficacy of including some of the rarer species. This chart is (presumably) for initiates, not “experts”. Including gull species with low frequency of occurrence might be unnecessarily confusing to a novice.
This chart is intended to be a tool. Like all tools for identification, it has its limitations and like all guides, is incomplete. It represents a piece of the larger puzzle. It is not a solution. It will not replace all our other field guides. It will not replace field work.
But I never turn down a new tool when offered, especially if it’s free.