Thanks for the explanation Bill. I for one to not believe that the area should be extended in this way for several reasons. I do not know if anyone in the area reports their area lists to the ABA, but their rules say that any new metropolitan circle must be 50 mile radius from a defined point. There was a grandfather clause for existing areas such as Saint Louis. The traditional definition of the Saint Louis circle, by the way, is 50 miles from the city limits. I have no idea why and it does make for a very odd area, since the city has a rather odd shape. Anyone who wants to report a Saint Louis area total to the ABA should use the traditional definition. Personally, I feel that is better to stick with the traditional circle so that records and counts can be compared from year to year. The northern end of Carlyle Lake is a great deal more than a little more than 50 miles from Saint Louis. I have not measured it, but I think it is closer to 70 or 75 miles. Anyone should feel free to bird anywhere they want. Allowing an arbitrary border such as a city circle or a state line to keep you from a good birding area is just silly. However, when I am writing the WGNSS birding report I intend to stay with the traditional definition, unless there is some really significant reason not to. If anyone does not like this and would like to take over writing the monthly report for the WGNSS newsletter, please let me know. I would be quite happy to let them take on the responsibility.
David Becher has offered a good reply to Bryan's questions about Carlyle, and Illinois in general. I will add what I had mostly composed before I saw Dave's reply.
Fundamentally, birders tend to want to see interesting birds wherever they may be. We live in a bi-state region, with some excellent natural areas in both MO and IL, and so, in general, St. Louis birders have always worked both sides of the river. Each of us has his or her own preferences, of course: I tend to focus my own interest more in Missouri, but not to the exclusion of Illinois, which has not only a bunch of fine places to visit but also a large and active birding community of its own and organization of its own. (Sidebar: I would recommend membership in the Illinois Ornithological Society to any St. Louisan, second only to membership in the Audubon Society of Missouri.) The same will hold true of any region on the border between states.
To create resources like lists and guidebooks, some boundaries must be drawn. Historically, the St. Louis area has drawn that boundary as a somewhat warped circle, 50 miles in all directions from the City limits. There is no special reason for this except (I assume) that it was a handy measure that included all areas that people could easily reach in a day trip. Once somebody fixed it at 50 miles, there it remained. Our St. Louis area guidebook (Birds of the St. Louis Area: Where and When to Find Them) observes it, and so have all previous area checklists, including the one by Randy Korotev that preceded the new one by Josh Uffman, now on line at www.mobirds.org.
Carlyle Lake is on most area birders' radar because it is our largest body of water; as such, it holds a special attraction for birds that seek large bodies of water, like loons, large grebes, certain rare migrants like Sabine's Gull, and jaegers. All of these have been seen on the Missouri side, but more rarely. Moreover, Carlyle also offers some great public-access areas (two state parks, many Corps of Engineers sites) and also a whole lot of farmland that provides very good back-road birding at times. So it's an excellent area for a day trip and for the prospect of something unusual.
Now, Carlyle Lake came into existence long after the 50-mile limit did. It turned out that only part of the Carlyle area, and only part of the lake, actually fell within that limit. This included the southern end and the commonly-visited parks, but not some other areas farther north and east, where there is nevertheless a lot of good birding, and where some rarities have been observed over the years. Previous lists have respected this limit and omitted those few species, but the large parts of the Carlyle area that did fall within the limit have always been considered part of the St. Louis area (as Dave mentions).
Most recently, it has come to seem artificial to leave out the other parts of Carlyle: they are available to us and are visited somewhat regularly by St. Louisans, in addition to being covered intensively by Dan Kassebaum and others who report on what they find. These areas are almost certainly visited by St. Louisans more than any other area that was previously outside the boundary. It has come to seem reasonable that our somewhat-warped circle should be warped slightly more to include all of the Carlyle area, and so the new online checklist does that. That's allónot really a big deal.
In practical terms, the decision to include all of Carlyle does not affect any of the status designations in the checklist; the only effect is to include accidentals that have occurred in the farther reaches of the Carlyle area (example: Gray Kingbird).
I hope this helps with the history part. Undoubtedly there are some people out there who know it in more detail than I do.