My concept has gone through various versions over the years as I learned more about some of the world's great birds, and as I refined my thinking on the topic. This is my third or fourth major version of the list, and I still dicker with it now and then.

My first effort was during college, in about 1974. I created a loose-leaf binder before my first world birding trip (which was to Colombia in 1975) with my initial choices, each one represented with a page that included a photo of some artwork and hand-written details and a map. [I couldn't find a picture of Hose's (Blue-bellied) Broadbill, so I tried painting my own.] I considered this my "most wanted world birds" list, and since it was a loose-leaf notebook, the choices could be rearranged as my thoughts changed over the years. Back in 1974, my "top 50" choices included birds such as Ivory-billed Woodpecker, Ou, Imperial Woodpecker, Kauai Oo, and others then nearing extinction. None of these are included now, even though some are rumored to have a tenuous hold on existence.

In my initial project, as I was able to observe some early choices (e.g., Scarlet Macaw or California Condor, right) they dropped off the list and new selections were added. I'd stamp "Observed" on the old page and write in a few details of my own sighting. My original "top 50" list in 1974 included 10 pheasants and 4 curassows. Although all were wonderful birds, that was just "too many chickens," as Guy McCaskie said when he saw the binder, and I've since made a conscious effort to diversify among the bird families.

In the next major incarnation of the list, placed on my web site in 1999, whether or not I'd personally seen a bird became irrelevant (except to me!) in evaluating the "best birds" of the world. Otherwise my general concept remained similar but I added a layer of "requirements" that forced diversity across the glove, limiting myself to only 10 "best birds" each from Asia and the Neotropics, 7 each from Africa & Australasia & the Oceanic Island (Madagascar etc.), 3 each from the Nearctic & the Western Palearctic, 2 pelagics in the Ocean realm, and 1 in Antarctica. But forcing myself to include a certain number of North American or European species, instead of some tropical birds that captured my imagination more, eventually became tiresome. These restrictions have been abandoned.

In preparing the predecessor to this current version, I assigned points between 0–5 in five separate categories: (1) how impressive, (2) how unique, (3) how rare, (4) how hard to find, and (5) special circumstances, and tallied the points on a spreadsheet. Here's a bit more on the system:

• Impressive? Big powerful raptors, huge albatrosses and cranes, and gorgeous tropical birds are "more impressive" to me than cisticolas or Cookilaria petrels. Although I love cisticolas and have done research on the small Pterodromas, we humans are stirred by wildlife that is big, fast, fierce, and colorful. On the other hand, in some species sexual dimorphism has produced spectacular males and smaller, drabber females (e.g., hummingbirds, manakins, birds-of-paradise). I have taken this into account to some degree, but still chose species in which it is the male that is "impressive," recognizing that sometimes the birder must "settle" for views of the less-impressive female or young. I also chose one bowerbird whose bower is overwhelmingly impressive, even though both sexes of the bird itself are very plain.
• Unique? The Kagu and Shoebill are unique birds and rate "5" in that category. Contrast that with the seven blue cotingas the genus Cotinga. Each is an absolutely stunning bird but none is "unique" with six close relatives looking equally beautiful. When it narrows down to just two or three similar birds, however, I begin to think of them as almost unique. To facilitate the list and create diversity, I permitted myself the choice of "any" of three or more closely-related species (usually within the same genus) when (a) as a group they are indeed unique, (b) together the sibling species form a superspecies in a similar geographic region, and (c) each of the various species is scarce and hard to see. You will thus find the choices any Tragopan, any Kiwi or any Cassowary; in a way this makes the project the "top 60" birds, but I can live with that. However, when there are only two such similar species, each is entitled to a separate place on the list when they individually score high enough in the other categories. Such pairs included are both rockfowl, both cock-of-the-rocks, and both huge white cranes.
• Rare? Almost all birdwatchers enjoy rare birds; it is a special feeling to be in the presence of something rare. I have often referred to BirdLife International's (2000) Threatened Birds of the World for population estimates. In general, the rarer a bird is the more it is desired. Note, however, that I have not included in my consideration those species teetering on the edge of extinction where a currently extant population is not proven (e.g., Ivory-billed Woodpecker, Ou, Night Parrot, Kinglet Calyptera, White-eyed River-Martin), even when it is possible the species still exists.
• Hard to find? This is not the same thing as "rare." The Seychelles Magpie-Robin Copsychus sechellarum was definitely rare when I saw it — only 23 birds left in the world — but it was not hard to find. Assuming you had time and money, you could fly to the Seychelles easily and no political turmoil prevents that; you could then fly to Fregate I. in a small plane, land and see the magpie-robin within a short level 10 minute walk. In contrast, while the Kakapo currently exists on only a couple tiny islets (just as does the magpie-robin), it is very hard get there. They are entirely off-limits to non-researchers and even if you volunteered several weeks of your time, you must be willing to volunteer on their schedule, making it very difficult to plan. And no amount of time or money will guarantee you a look at a Congo Peafowl.
• Special circumstance? Almost any bird considered for the list is special; this category is my own much more subjective category and may include the bird's history. The Short-tailed Albatross was almost entirely wiped out a half-century ago; when I began birding it was considered impossible to see. So when I did see one, it was extra special for me. The California Condors became extinct the wild in 1987 when the last six were captured for captive breeding, but now two of those original birds are flying again, and others are attempting to nest. The Mauritius Kestrel went through an evolutionary bottleneck when only a lone breeding pair remained in 1974, and they have recovered. I've always wanted to see these birds. In addition, birds like Great Argus and Long-tailed Ground-Roller were considered near mythical when I started birding the world about 1975, and the search for them has been a wonderful quest. This category is personal and elevates a few birds to the list over some equally qualified candidates that don't mean as much to me.

Let me explain how my system works with two examples. Palmchat Dulus dominicus of Hispaniola is generally assigned to its own monotypic family; it is thus "unique" in some sense and might score at 3 or 4 in that category. But it is neither "impressive" nor "rare," and it is about the easiest native bird to see in the Dominican Republic. You just have to get there. So the points in those categories might be 0, 0, and 1. Without any special personal connection or history, it will total out at about 4 or 5 points.

Or consider my personal web moniker, the Swallow-tailed Gull Creagrus furcatus (right) of the Galapagos Is., and wintering in the Peru Current. It is "unique" in its family as a night-feeding gull but it still is just a gull (give it 2 points). It is rather scarce (3 points) but surely gulls cannot rate too high as "impressive" (maybe 3 max) and it is easy to see if you get to the Galapagos or off coastal Peru, in season (say 2 points). So it might max out at about 10 "objective" points. Even its vagrancy to Monterey Bay, and my special affection for it, can't kick it up enough to make my "top 50," even though it and Ross's Gull Rhodostethia rosea might be the world's "best" gulls.

I wanted diversity around the globe, and across the bird families; these 50 choices belong to 36 different families. There are many tropical birds included but also some long-distance migrants, some species of the cold north, and one from deepest Antarctica. Several birds have ranges across several continents or oceans, but my choices essentially fall as 13 in Asia, 11 in the Neotropics (Central & South America), 8 in Australasia, 6 in Africa, 5 in the Pacific and two in the Indian Ocean, 4 in North America/Caribbean, and 1 in Antarctica. They include 4 birds-of-paradise, 3 pheasants, 3 parrots, 3 cotingas, 2 eagles, 2 seabirds (inc. penguins), 2 pittas, 2 cranes, 2 rockfowl, a condor, a guan, a bustard, a wader, an owl, a hummingbird, a trogon, a barbet, a broadbill, a ground-roller, a manakin, a vanga, a bowerbird, a wattlebird, a helmet-shrike, a grasswren, a myna, a tanager, a honeyguide, and 8 species assigned to their own monotypic families.

In Nov 2003 and again in Feb 2010 and Jan 2012, I made slight revisions to some choices; dropping six prior picks to add six new ones, and somewhat reordering the picks. As noted above, a lot of other birds are also in the running for the "Top 50" and these final choices are somewhat agonizing....

You can also see comments on my list from other birders. I thank Chris Carpenter, who photographed the Diademed Sandpiper-Plover (Chile), for use of his photo and to all other photographers and artists who made this project possible (providing photos or art on linked pages). I am also indebted to the many world birders who shared their thoughts on this topic, including Rita Carratello, S.F. Bailey, Victor Emanuel, Jon Hornbuckle, the late Stuart Keith, Jon King, Harold Lebo, Murray Lord, Blake Matheson, Phil Rostron, Dan Singer, and the late Arnold Small.