Birds are feathered creatures in the Class Aves. Without getting into too much high school biology, suffice it to say that ornithologists divide birds into Orders, Orders into Families, Families into Genera, and Genera into Species. The subject of these pages is the Family. Van Tyne & Berger (1959) wrote: “By definition, a family is a monophyletic (i.e., it stems from a single ancestral species), and many families are so well marked that there is not the slightest disagreement among ornithologists about which species should be included in those families... Other families have not evolved far enough to be sharply demarked and there is considerable disagreement among ornithologists about where the boundary lines should be drawn.” These general principles still apply, although now many (including me) try to balance traditional "families" against recent biochemical data, or try to reconcile conflicting lines of evidence.

When I was a child, one of my favorite books was Austin and Singer’s (1961) Birds of the World whose subtitle was “A survey of the twenty-seven orders and one hundred and fifty-five families.” It splashed lovely color paintings by Arthur Singer of representatives of all the world’s birds among the popularized text by Oliver Austin. I knew from a very young age that I’d like to see these birds or, at a minimum (since it is impossible to have the necessary time, money, and access to see all the world’s birds) a representative of each of these families. But it is much easier to say “I’d like to see at least one representative of all the families of the birds of the world” than to determine what that means, let along have the time, money, energy, and opportunity to accomplish the goal.

DEFINING “FAMILIES OF THE WORD”

The first problem is defining the “families of the world.” Much as been learned about avian classification since my childhood. It could have become a stated goal to see at least one bird in each of the 155 families that I learned about as a boy, but that would not satisfy me. In 1980, when I was first thinking of seriously birding the world,  Terres’ Encyclopedia stated “Ornithologists agree generally that there are about 170 families of birds in the world, each of which may contain anywhere from 1 species to more than 300.” By the time I realized it was actually possible to reach for such a prize in my mid-40s, even that statement had changed. I now wanted my list of families to be both current and factually defensible.

In the 1970s, one of the most widely accepted arrangements was that proposed by Morony, Bock & Farrand (1975). Used by many museums to arrange their specimen collections, they listed 25 orders (but 54 “suborders”) and 159 families. Within a few years, the “155 families” of my childhood or the 159 of Morony, Bock & Farrand had been enlarged to “about 170.” This was because detailed studies of external or internal morphology (often termed “cladistic” studies) showed that some supposed “families” were paraphyletic (i.e., derived from more than one ancestral line) and therefore violated the fundamental definition of a Family. They had to be divided into additional families to properly show evolutionary relationships. [During this period the "Peters' checklist series" (a multivolume set of which I have looked at only one in detail; Mayr & Cottrell 1979 -- and it did a good job with seabirds) was also influential.]

The Morony, Bock & Farrand’s list had an obvious downside. They had thrown together all sorts of birds into the family Musicapidae: thrushes, Old World flycatchers and Old World warblers were grouped together with African wattle-eyes, Chinese parrotbills, and Australian wrens, many of which proved to be evolved from quite different ancestors. Even though the Handbook of the Birds of the World project that began in the 1990s (del Hoyo et al. 1992 and successive volumes) said it was based on Morony, Bock & Farrand, this was not really true. Rather, that project (often known by the abbreviation “HBW”) starts with Morony, Bock & Farrand and enlarges upon it. The HBW website originally stated that the project would feature 176 families (a significant enlargement on the 159 proposed earlier) but in corresponding with the authors I have learned that their current tentative plan for the series includes 196 families!

Much of this enlargement comes from the innovative studies of avian relationships based on egg-white proteins, then on DNA-DNA hybridization, and then on mitochondrial DNA, which began being published in the 1980s. Perhaps the most influential were the works of Charles Sibley and John Ahlquist (such as Sibley & Ahlquist 1983, 1990). Sibley collaborated with Burt Monroe to publish a new and quite different arrangement of the birds of the world in Sibley & Monroe (1990). It had 23 orders (and 32 sub-orders) and 133 families (plus one “Incertae sedis” [Broad-billed Sapayoa] with which they didn’t know what to do). Their listing totally upset the traditional applecart, listing penguins and loons -- which are usually right at the front of any world list -- well past the middle of the arrangement, and found ducks almost adjacent to woodpeckers (to mention just a few of the more provocative proposals). Few scientists have followed this revolutionary sequence, and it has been subject to extensive criticism in the professional literature, but some of their work has gained wide acceptance (e.g., that the corvids arose in Australasia).

While Sibley & Monroe restricted the Musicapidae to thrushes and Old World flycatchers, avoiding the odd “dumping ground” which Morony, Bock & Farrand had constructed for this family, they introduced new conglomerations in the Corvidae and Fringillidae. The Corvids, traditionally comprised of the crows and jays, was now proposed to be a family which arose in Australasia and spread throughout the world. Included were such Australian groups as quail-thrushes, sittellas, and currawongs, plus birds of paradise, Old World orioles, cuckoo-shrikes, fantails, drongos, and African wattle-eyes, along with the crows and jays. In fact, they divided the single Corvid family into 7 “sub-families” and 16 “tribes.” Likewise, they lumped together the New World warblers, tanagers, sparrows, icterids, flowerpiercers, Hawaiian honeycreepers, and others into a single family [Fringillidae] composed of 3 sub-families, 9 tribes, and 993 species!

SEQUENCING THE FAMILY LIST

One other underlying concept deserves brief attention. Since any classification is intended to reflect evolutionary relationships, efforts in the late 19th century were directed in preparing a list of the “most primitive” to the “most advanced”, based upon the belief that Darwinian evolution brings “progress”. In such a classification, slime-sucking worms were low on the pyramid and humans are (obviously!) at the top. Among birds, the idea arose that crows and jays were the “most intelligent” of birds, so they should be listed last reflecting their position “atop the pyramid.” In the 20th century, most biologists (popularized in the writings of Stephen Jay Gould and others) rejected the concept of hierarchical “progress” in evolution. Recent classification have been intended to reflect a listing that goes from the oldest to the more newly-derived groupings (i.e., the most recently evolved). Mayr & Amadon (1951) and Wetmore (1960) were among those who believed that the nine-primaried birds, such as New World warblers, sparrows, icterids, and finches, were the most recently evolved and that they should, therefore, be at the end of the listing, with crows (which have ten primaries) being listed somewhat earlier.

What has arisen from these concepts is two competing groupings of the passerine birds. One group, which tends to be followed by European writers, still places the crows at the end. Examples are the lists proposed by Vaurie (1964), Voous (1973, 1977), and Morony, Bock & Farrand (1975). The other group, which tends to be followed by American authors, puts the nine-primaried passerines at the end. Examples include AOU (1977, 1998) and Sibley & Monroe (1990). The various competing “World Checklists” use one or the other of these styles, usually depending on whether they are produced in America or in Europe. That accepted as the listing standard by the American Birding Association (ABA), for example [Clements 1991 and supplements] concludes with the finches and icterids. Interestingly, so did the Handbook of the Birds of the Western Palearctic series (Cramp & Simmons 1977 and successive volumes), even though published in Europe. Alas, the on-going HBW project (published in Spain) places the crows very late in the sequence, and then concludes with the icterids.

At this point in time (February 2000), there is no single acceptable list of the Families of the World. Clements’ check-list (1991), for example, based largely on Gill (1990) but with his own modifications, is disappointing. It has 31 orders and 195 families (one of which, the Dodos, is extinct). Heavily influenced by Sibley & Monroe (1990), it seems to go off the deep end in the opposite direction of that book. Whilst Sibley & Monroe had only 133 families, the Gill/Clements listing raises various “subfamilies” and “tribes” to familial status, seemingly at random, leaving others behind. An example is the Magellanic Plover of southern South America, considered a Family [Pluvianellidae] by Clements but which Sibley & Monroe did not even raise to “tribe” status [some recent studies suggest it is more closely related to sheathbills than to plovers]. And why does Clements separate the Eared-Nightjars [Eruostopodidae] from Caprimulgids (a Sibley-Monroe innovation) when he does not separate the Asiatic and Australasian frogmouths [Batrachostomidae & Podargidae , respectively], another Sibley-Monroe proposal? I have personal experience with all these groups, and to my amateur eye an eared-nightjar sounds and acts a lot more like an ordinary nightjar than does an Asiatic frogmouth to the Australasian species. The latter birds strongly recall New World potoos, while members of the genus Bathrachostomus (of which I’ve seen  & heard three in the Philippines & Sumatra) are the strangest medussa-headed birds one could ever hope to encounter. If anything, which group deserves Family status should be reversed from Clements’ listing.

And talk about going off the deep end! The 7th ed. AOU (1998) list of North American birds promotes everyone and his brother to Family status, including the monotypic Olive Warbler [Peucerdramidae] and Bananaquit [Coerebidae]. Let that committee loose on the world at large and we would have 250 or even 300 families!

CHOOSING A FAMILY LISTING

In the end, I decided what was needed was a family list grounded in both tradition and reality. It would not leap to accept brand-new proposals, but would also be willing to move away from traditional concepts when new material had been published, widely reviewed, and accepted (such as the New World vulture/stork relationship referred to previously). It appears that the 12-volume HBW project is within my concept of a reasonable list. The first five volumes seem to make reasonable, conservative, but forward looking choices. Magellanic Plover is not elevated to Family level (Sibley 1996 does so but admits it is philosophy, not based on biochemical evidence) but the traditional Ibisbill [Ibidorhynchidae] is (Sibley-Monroe considered it just an odd member of the avocet-stilt assemblage). Shoebill is retained as a family of its own, but the cuckoos are not split into three groupings as some have proposed. Nightjars and Frogmouths remain families without further innovation. These are traditional choices, but some innovation has been accepted. The Plains-Wanderer [Pedionomidae], long thought to be related to Buttonquail [Turnicidae], is moved to the shorebird-wader order [Charadriiformes] based on new information. And, given strong evidence, the Psittaciformes (parrots) are separated into two separate families: parrots [Psittacidae] and cockatoos [Cactuidae]. For now, then, I use the HBW list of families as my starting point for an “acceptable” list. [This is not an endorsement of everything in those books, however. I have found some very debatable species splits, some sections that overlooked important published information, and a few outright errors. Fortunately, the photos are great and the introductory text to each family reasonably well done.]

I was able to obtain a full tentative list for the remaining HBW volumes from the primary editors of the series (many thanks!) in 1999, and James Clements informed me of further revisions to their proposed listing in Feb 2000. Rather than the 176 families their Internet listing says will be featured, the current tentative list is 196. Obviously, Sibley & Monroe’s huge Fringillidae will be broken up into more traditional components, including finches and icterids as separate families. The Musicapidae is limited to Old World flycatchers, with Old World warblers and  thrushes retaining separate identities. The accentors (lumped by Sibley-Monroe in the Passeridae) will have their own family. Yet some of their tentative decision do not seem reasonable to me. The retention of the Sharpbill (Oxyruncidae) and and plantcutters (Phytotomidae) as families is suspect, since most recent authorities (e.g., Ridgely & Tudor 1994) merged them into the Cotingas. Leaving the Wallcreeper in its own family, and retaining Hypocolius as a family, both seem quite dated. Retaining asities as a separate family, despite the evidence by Prum (1993) that they are best considered a subgroup within the Broadbill assemblage, is also somewhat suspect but Sibley (1996) continued to accept the asities' family status despite noting the new information. I include on my list all the families on the HBW list for the present, and have added a very few others. An explanation appears at the bottom of my family list page.

I thus list 202 bird families, but I have revised the sequence dramatically to approximate the “American approach” to sequencing families as exemplified by the AOU’s 7th ed. Check-list (1998).

DEBATING SPECIES CONCEPTS

In all this talk about Families, I would be remiss if I didn’t mention the current debate over the species concept. Throughout the 20th century, classifications of the birds of the world have relied upon the biological species concept (BSC). Mayr et al. (1953) defined a species as an interbreeding, or potentially interbreeding, group of birds that does not in nature interbreed significantly with any other group. In other words, a group of birds that has evolved isolating mechanisms that preclude widespread interbreeding with other groups of birds. Isolating mechanisms may be plumage, vocal, behavioral or other differences that serve to let the birds “define themselves” as species in nature. Hairy and Downy woodpeckers ranges overlap widely in North America, but they interbreed only within their own kind, thus defining themselves as “species.”  The difficulty with the BSC has always been with the difficulty in determining whether groups of birds that never meet in nature would or would not interbreed freely but for the geographic barriers that exist. Those determinations are the subject of frequent debate and the preferred fashion of the times. “Lumping” closely related but geographically disparate species was “in” during the 1960s and 1970s, but “splitting” became more fashionable in the late 1980s and 1990s. My belief is that these are not “fashions” in the sense of random peer-group acceptance, but rather a recent recognition that vocalizations and breeding phenology are often key isolating mechanisms. With many recent studies of obscure birds and better research into vocalizations and biology, ornithologists have been in a better position to make the “informed guess” as to whether two far separated groups of birds would or would not likely interbreed.

However, in a reaction to the apparent randomness of some ornithological decision making, a number of professionals have recently been promoting the phylogenetic species concept (PSC). It considers as a species any group of birds which shares a diagnosable and heritable trait not shared by other groups. The net effect of this approach -- which does not consider what actually happens in nature -- is to elevation many taxa to “species” because they are at the end of a particular evolutionary clade. Using the BSC there are perhaps 10,000 species of birds in the world, but using the PSC produces many, many more -- perhaps 50,000 “species.” These concepts have been the subject of lively debate in the professional literature and in 1997, an entire issue of the Bulletin of the British Ornithological Club was devoted to this topic. Interesting introductions to the problem are provided by Sibley (1997) and Greenwood (1997). Some of the best-stated arguments in favor of the PSC are by Zink & McKitrick (1988) and Zink (1997); some of the strongest arguments supportive of the BSC are outlined by Collar (1997) and Snow (1997). Just recently, a fine explanation and defense of the BSC is on-line; see Ernst Mayr's article (first published in 1996).

It is my amateur “field ornithologist” opinion that those supportive of the BSC have the better arguments. I use the term “species” in these pages as that word is defined by the BSC. Within this construct, the checklist of Sibley & Monroe (1990) has been much more influential than has there radical reorganization of higher taxonomy. That work recognized 9672 species. After retirement, Charles Sibley continued to compile information for publication in diskette format (with which I assisted in small part). In his last note to me before his death, he said his species list was up to about 9980 birds. These additions were primarily the result of better insight into likely isolating mechanisms of island-bound birds, but also represent the continued discovery of several new species of birds each year.

Clements’ 4th ed. Checklist (1991) also listed about 9700 species, and his supplements (published by the ABA in Winging It) have added about 70 more. Unfortunately, Clements and others have had a tendency to blithely “accept” any published proposed change in taxonomy without consideration. For example, Howell & Webb’s (1995) Field Guide to Mexico “split” a wide variety of taxa in their main text. But if one reads their introduction, you discover that these are tentative proposals at best, not usually supported by sufficient research. In some cases, the authors themselves have published additional research to support the suggestions (e.g., Howell 1993) but many remain bare proposals only. One would think that reasonable people would require more before adopting a change from the status quo, but I see some authors blindly following the Howell-Webb “splits” as if they were really something important. In any event, the references to “number of species” within these family pages is largely taken from Clements’ 4th ed. and supplements.

SUMMARY

For now, I have followed the HBW choices for the “families of the world" except that I have added six: two AOU families, two Sibley & Monroe families (three families of barbets since toucans are retained as a family; there is a major logical problem if this is not done), and two families elevated by African specialists (ground-hornbills & oxpeckers).  I generally use Clements’ 4th ed. (1991) for species counts. However, each of these texts are not without problems and, as stated early on, there still is no single acceptable list of either “families” or “species” of the world’s birds. There may never be. Yet I find the topic interesting, and I truly enjoy traveling the world in search of its unique and special birds.

Of these 202 families now tentatively accepted, I have currently (June 2001) seen representatives of 196 and have photographed at least one species in 182 families. I hope to locate species in the remaining 6 families (Shoebill, Sheathbills, Oilbird, Plantcutters, Bristlehead, Sugarbirds) before the end comes and with any luck, take photos of most of them.

Literature Cited

American Ornithologists' Union. 1983. Check-list of North American Birds. 6th ed. A.O.U.,  Washington, D. C.
American Ornithologists' Union. 1998. Check-list of North American Birds. 7th ed. A.O.U.,  Washington, D. C.
Austin, O. L., and A. Singer. 1961. Birds of the World. Edited by H. S. Zim. Golden Press, New York.
Brown, L. H., E. K. Urban, and K. Newman, eds. 1982. The Birds of Africa. Vol. 1. Academic Press, London.
Clements, J. F. 1991. Birds of the World: A Check-List. 4th ed. Ibis Publishing, Vista, CA.
Collar, N. J. 1997. Taxonomy and conservation: chicken and egg. Bull. Brit. Ornithol. Club 117: 122-136.
Cramp, S., and K. E. L. Simmons, eds. 1977. The Birds of the Western Palearctic. Vol. 1. Oxford Univ. Press.
del Hoyo, J., A. Elliott, and J. Sargatal, eds. 1992. Handbook of the Birds of the World. Vol. 1. Lynx Edicions, Barcelona.
Ehrlich, P. R., Dobkin, D. S., and Wheye, D. 1988. The Birder's Handbook. Simon and Schuster, New York.
Gill, F. B. 1990. Ornithology. W. H. Freeman & Co., New York.
Greenwood, J. J. D. 1997. Introduction: the diversity of taxonomies. Bull. Brit. Ornithol. Club 117: 85-96.
Howell, S. N. G. 1993. Taxonomy and distribution of the hummingbird genus Chlorostilbon in Mexico and northern Central America. Euphonia 2: 25-37.
Howell, S. N. G., and S. Webb. 1995. A Guide to the Birds of Mexico and Northern Central   America. Oxford Univ. Press, New York.
Mayr, E., and D. Amadon. 1951. A classification of recent birds. Amer. Mus. Novitates 1946: 453-473.
Mayr, E., and G. W. Cottrell, eds. 1979. Peters' Check-List of the Birds of the World. Vol. 1, 2d ed. Mus. Comparative Zool., Cambridge, MA.
Mayr, E., E. G. Linsley, and R. L. Usinger. 1953. Methods and Principles of Systematic Zoology. McGraw Hill, New York.
Morony, J. J., W. J. Bock, and J. Farrand. 1975. Reference List of the Birds of the World. Amer. Mus. of Nat. Hist., New York.
Prum, R. O. 1993. Phylogeny, biogeography, and evolution of the broadbills (Eurylaimidae) and asities (Philepittidae) based on morphology. Auk 110: 304-324.
Ridgely, R. S., and G. Tudor. 1989. The Birds of South America. Vol. 1: The Oscine Passerines. Univ of Texas, Austin.
Ridgely, R. S., and G. Tudor. 1994. The Birds of South America. Vol. 2: The Suboscine Passerines. Univ of Texas, Austin.
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Sibley, C. G. 1997. The species problem. Birding 29: 215-219.
Sibley, C. G., and J. E. Ahlquist. 1983. Phylogeny and classification of birds based on the data of DNA-DNA hybridization. Current Ornithol. 1: 245-292.
Sibley, C. G., and J. E. Ahlquist. 1990. Phylogeny and Classification of Birds: A Study in Molecular Evolution. Yale Univ. Press, New Haven, CT.
Sibley, C. G., and B. L. Monroe, Jr. 1990. Distribution and Taxonomy of Birds of the World. Yale Univ. Press, New Haven, CT.
Snow, D. W. 1997. Should the biological be superseded by the phylogenetic species concept? Bull. Brit. Ornithol. Club 117: 110-121.
Terres, J. K. 1980. The Audubon Society Encyclopedia of North American Birds. Alfred A. Knopf, New York.
Van Tyne, J., and A. J. Berger. 1959. Fundamentals of Ornithology. John Wiley & Sons, New York.
Vaurie, C. 1964. The Birds of the Palearctic Fauna. Witherby, London.
Voous, K. H. 1973. List of recent Holarctic bird species. Nonpasserines. Ibis 115: 612-638.
Voous, K. H. 1977. List of recent Holarctic bird species. Passerines. Ibis 119: .
Wetmore, A. 1960. A classification of the birds of the world. Smithsonian misc. coll. 139 (11), Smithsonian Institution, Washington, D. C.
Zink, R. M., and M. McKitrick. 1988. Species concepts in ornithology. Condor 90: 1-14.
Zink, R. M. 1997. Species concepts. Bull. Brit. Ornithol. Club 117: 97-109.
 

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