Ornithologists have never agreed upon what constitutes a "family" of birds. It is a taxonomic classification that is finer than "orders" and broader than "subfamilies," "tribes," or "genera." There used to be fairly good agreement that there were 27 orders of birds, but Sibley & Ahlquist (1990) and Sibley & Monroe (1990), using molecular evidence (primarily DNA-DNA hybridization techniques), opted for 22 orders of birds and various "parclasses," "superorders", "infraorders," "parorders" and so on. There never was much agreement on how many families there were, and with the applecart upturned by biochemical evidence, there is currently little harmony on this topic. I've decided that the approach of the Handbook of the Birds of the World seems best. They acknowledge the molecular evidence -- and follow it where it appears conclusive or is confirmed by other lines of analysis -- but in less certain areas they retain many traditional families. The work of Sibley and colleagues is not without analytical problems (e.g., see Harshman 1994 for just one critique), and it seems wisest to me to "go slow" and adopt their conservative approach. I prefer the Handbook list over a similarly "pick and choose" set of families used by Clements (1991) or the different set in Clements (2000). Thus my list on this web site is the Handbook's 201 families (assuming that their preliminary choices for upcoming volumes hold steady) plus one more that seems "obviously" correct to me [Ground-Hornbills separated from Hornbills, following Kemp (1995)].
This means that there are a group of "proto-families" or "pseudo-families" that have been accepted by other authors, but which I do not include among my 202 families. The more important of these are discussed here. In 1998, Harry Howard & Derek Scott undertook to try to see all the bird families of the world (their story is in Howard & Scott 1999). They used Clements (1991) list [194 families] as their starting point, then added seven extra from Sibley & Monroe (1990), and then noted that 32 other groups had been family status by at least one other author in the 20th century (they saw 28 of these 32). We need not concern ourselves with quite that many; some of the older suggestions were idiosyncratic or have been discarded.
For example, the Boat-billed Heron (right) was often considered a monotypic family, the "Cochlearidae," until the A.O.U. (1983) downgraded it to subfamily status. Biochemical and other evidence has shown that it is clearly just a big-billed night-heron; it is not even thought to be subfamily now (e.g., A.O.U. 1998). But it is still a great bird to find in the Neotropics (coastal mangrove swamps of Mexico to the Brazilian Pantanal). It was one of the 155 families that I learned as a kid (e.g., Austin & Singer 1961) and therefore has always seemed very special to me. There seems little likelihood, however, that it will ever be considered a "family" again.
It seems more important to focus on the proto-families that are simply a matter of degree. Some major authorities -- such as the American Ornithologists' Union (1998) or Sibley & Monroe (1990) -- considered some groups worthy of family status, but the Handbook and many other writers believe them better defined as subfamilies. [Sibley & Monroe (1990), of course, dumped a whole lot of stuff into subfamilies or tribes... they lumped together, for example, the skuas, gulls, terns, skimmers, and alcids into a single family. Sibley (1996) explained that this was done by the mathematics of "melting points" in DNA-DNA hybridization studies: the higher the temperature of the melting point that separated the DNA bonds, the closer the relationship. This "melting point" is a complex formula we need not explain here, but "delta values" between 9-11 were considered "families" while those with values between 7-9 were considered "subfamilies" and those between 4.5-7 were considered "tribes." Thankfully, few others have accepted this strictly mathematical view of defining "families," in part because it suffers from a presumption that the rates of evolution are the same for every bird lineage, a presumption that may not be true.] So I focus here on those groups that these influential authorities considered "families" but I do not:
THE A.O.U. FAMILIES
The most recent AOU Check-List (7th ed., 1998) elevated two groups to family level that few others consider worthy of this distinction (Sibley & Monroe did not, for example). These are discussed below. In addition, the AOU adopted the Sibley & Monroe position that their are three families of barbets:
The AOU (1998) does not explain why it considers the Bananaquit (three photos below) a monotypic family the "Coerebidae." Sibley & Ahlquist (1990), Sibley & Monroe (1990), and Bledsoe (1988) all showed through molecular evidence that the "honeycreeper family" ["Coerebidae"] were simply odd tanagers, and that the Bananaquit was just a part of this assemblage. Sibley & Monroe (1990) did not give it any special status at all -- it is just one of the genera of tanagers (and the tanagers were just a tribe of a huge emberizid assemblage). Ridgely & Tudor (1989) considered it a monotypic subfamily -- equal with the tanagers -- "for convenience." The Bananaquit differs from other honeycreepers by building a large untidy globular nest, very unlike the cup nests of dacnises, honeycreepers, and most tanagers.
The other "AOU family" is another monotypic form (meaning it has only one member): the Olive Warbler ["Peucedramidae"] (right). It is a small passerine primarily resident in pine-oak forests of mountains from southeastern Arizona to Nicaragua. It acts like a New World warbler -- and is usually considered a New World warbler [Parulidae] but the DNA evidence shows it to be of a distinct lineage. The AOU also points to differences in morphology and breeding biology (George 1962, 1968) in raising it to family status. What George (1968) found is that it had a cylindrical (not compressed) bone in its hyoid apparatus -- as found in all Old World songbirds -- which is not found in any other New World nine-primaried passerines except the Swallow-Tanager Tersina viridis. It also had a nest more like a kinglet, and eggs unlike parulids (George 1962). For these reasons some thought it might actually be an Old World warbler [Sylviidae].
DNA-DNA hybridization showed it a sister species of fringillid finches -- not a warbler at all. This was so unexpected that even Sibley & Monroe (1990) said that the "result requires confirmation or contrary evidence." I suspect that the Handbook project is awaiting that additional evidence, and holding the Olive Warbler as a New World warbler as the conservative position.
It is not hard to find an Olive Warbler, either in the mountains of southeast Arizona or the Mexican highlands, so -- like the Bananaquit -- it is easy to "bank" for one's world bird families quest.
The Sibley & Ahlquist (1990) and Sibley & Monroe (1990) sequence was revolutionary, and only now are ornithologists able to better pick out the nuggets from what at first appeared to be a complete topsy-turvy listing. The proposals feature more "lumping" at the family level than splits: e.g., a huge Crow family [Corvidae] lumps together such diverse birds as ravens, woodswallows, cuckoo-shrikes, birds-of-paradise, drongos, fantails, ioras, monarchs, bush-shrikes, and vangas. Thankfully, few modern authorities are accepting these radical proposals at the family level. However, some of their "splits" make a lot of sense and have been adopted widely, including raising the two groups of berrypeckers in New Guinea to family level. The AOU (1998) adopted their split of barbets into three families (and lumping the toucans with New World barbets), as discussed above and on my barbet family page. Additional similar "splits" to be discussed on family pages are:
The Magpie Goose is found only in swamps and wet grasslands of southern New Guinea and northern Australia. It is not normally one of the Australasian specialty families that come to mind when one thinks about Australasia (I think of birds-of-paradise and fairy-wrens and bowerbirds and emus and cockatoos), but given the Sibley & Monroe split, its not a bad idea to search a flock out when in that part of the world.
The "Dendrocynidae" is composed of the nine species of whistling-ducks in the genus Dendrocygna. These are found around the world -- mostly in the tropics -- and one species [Fulvous Whistling-Duck D. bicolor] is found on all the major continents (missing only in Australasia and Antarctica). The White-faced Whistling-Duck illustrated here is also found widely in east and southern Africa, Madagascar, and Central and South America; I have my own photos but I liked the Zimmermans' shot better.
There is yet another group of birds -- variously placed with the manakins or the cotingas or the tyrannid flycatchers -- that seem to be related to each other but the relationship of the group with other groups is not understood. This is termed the "Schiffornis assemblage", after the better known "Thrush-like Manakin" or Thrush-like Schiffornis Schiffornis turdinus which ranges widely from Mexico to Brazil. The group includes two species of Schiffornis, the localized White-naped Xenopsaris Xenopsaris albinucha of South America, the widespread becards in the genus Pachyramphus (including Rose-throated Becard P. aglaiae which ranges north into the U.S.), the tityras, the Shrike-like Cotinga Laniisoma elegans (which may not be a cotinga), and two mourners in the genus Laniocera (Prum & Lanyon 1989). The AOU (1998) also lists this group as "Incertae Sedis" among the tyrannoids. It could be this assemblage will form a new family some day. Johansson et al. (2002) conducted further biochemical analysis, and considered this group to be a sister group of a broadened Cotingidae [Cotingas, including Plantcutters and Sharpbill]. If that analysis proves correct, this group might be considered either a new family or a subfamily of the Cotingas.
OTHER PROPOSALS, NEW and OLD
There is much confusion about a recent proposal to elevate the Magellanic Plover Pluvianellus socialis of southern South America as a monotypic family ["Pluvianellidae"]. This is not a Sibley & Monroe (1990) split; indeed, they did not set it apart from other plovers at all. However, Charles Sibley (1996) elevated it to family status in his diskette update to Sibley & Monroe after Burt Monroe's death. Yet the very pages that make this proposal acknowledge that the suggestion is not based on biochemical evidence but instead on some unique behavioral characteristics (e.g., food transported in its crop and regurgitated for the young or its turnstone-like behavior). Sibley's suggestions is entirely philosophical: "Placing it in a monotypic family calls attention to its unique or unusual features and may attract additional study." In my opinion this is the equivalent of "political correctness," but despite this weak reason for family status, Clements (2000) considers it a separate family. It is true that osteological studies (Strauch 1978, Chu 1995) place the Magellanic Plover in a different lineage than other plovers, closer to the sheathbills -- so the jury is still out on this one. We really need more information; the Handbook account (Piersma 1996) currently considers it a subfamily of the plover [Charadriidae].
Other older proposals for family status that now appear to have bitten the dust are:
For one interested in searching for the bird families of the world, it makes sense to seek the 204 listing on my index portal page. These are the 196 to be used in the Handbook of the Birds of the World series (assuming they stick with their tentative proposals for groups in volumes not yet published) plus my acceptance of 8 other families.
The Sibley & Monroe splits are mostly not too difficult: try to see all five groups of cuckoos, all three groups of kingfishers and barbets, a whistling-duck, and an eared-nightjar (not too hard since they range from India to Australia). More specialized trips are needed for Magpie Goose and another for one of the Asian Frogmouths.
Assuming one wishes to be well diversified in the various approaches to "bird families," this all adds up to some 217 families and proto-families [if one includes the Magellanic Plover]. As to the others -- from Boat-billed Heron to Swallow-tailed Tanager -- they are great birds in their own right, but my feeling is that none stands a chance of surviving as a true "family" in the long run.
Photos: The Boat-billed Heron Cochlearius cochlearius was photographed in the Brazilian Pantanal in Aug 1999. The three shots of Bananaquit Coereba flaveola were taken, respectively (left to right): San Salvador I., Bahamas, in Nov 1980; St. Thomas I., U.S. Virgin Is., in Sep 1979; and on Bonaire, Netherlands Antilles, in Sep 1985. The Olive Warbler Peucedramus taeniatus was on Volcan Popocatepetl, Mexico, on 30 Dec 1995. The Magpie Geese Anserianas semipalmata were photographed by John Marchant in Hastie Swamp, Queensland, Australia, on 8 Nov 1982, and Dale & Marion Zimmerman took the White-faced Whistling-Duck Dendrocygna viduata shot at Lake Jipe, Kenya, in Sep 1981. The Plushcap Catamblyrhynchus diadema was in bamboo below Abra Malaga, Dept. Cuzco, Peru, on 17 June 1987. All photos © 2000 Don Roberson, except those by John Marchant and Dale & Marion Zimmerman, who hold those copyrights (used with permission); all rights reserved.
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