One of a Kind-- A Compiled List of the Monotypic Bird Families of the World

One of the most spetacular monotypic bird families: the Rail-babbler.
Photo taken in Malaysia by Jason Lee: https://flic.kr/p/fnUdt7
Used with permission, all rights reserved by photographer

There's something compelling about birds that don't fit into any of the "standard" bird categories. Harpy Eagles, Marvelous Spatulatetails, and Paradise Tanagers are fantastic, sure, but they are also simply exemplary members of familiar groups: the hawks, the hummingbirds, the tanagers. If you were going to describe a Scarlet Macaw, you would say "it's a really colorful parrot." But how would you describe a Kagu, or a Hoatzin, or a Bornean Bristlehead? These birds have no other living close relatives: they are distinct enough to be placed not just in their own genus but in their own family. Reading about exotic birds in far-flung locations, I became fascinated with these birds: in technical terms "monotypic families." As I did more research, I decided to put together a list of these unique species, a sort of roster of the world's most evolutionarily distinct and unique birds.

That turned out to be easier said than done, because there isn't a whole lot of consensus on what the bird families of the world actually are. Unlike species (which is defined as a group of populations that can interbreed: the Biological Species Concept), there is no set definition for what a family is. It's simply an evolutionary grouping narrower than an order and broader than a genus. The only real requirement is that it must be monophyletic (not to be confused with monotypic): that is, it must include all descendants, and only descendants, of a common ancestor. In a "tree of life," or phylogeny, a monophyletic group must be a branch, include all the twigs off of that branch, and only twigs from that branch.

In this case, blue and red are monophyletic groups and could be considered families. For green to be monophyletic, it must either be combined with blue into one large family, or split up into at least 3 families. In our example, the green would be barbets, and the blue would be toucans. "Clade-grade II" by Petter Bøckman 

To give an example, it was discovered that toucans evolved from a particular group of new world barbets. Previously, the toucans had been one family, and the barbets another. But now, instead of being two branches, the toucans were revealed to be only an offshoot of part of the barbet group. There are two ways to make this group monophyletic, and crucially, both of them are perfectly valid, and different authorities could reasonably adopt either. One option would be to subsume the toucans into the barbets, making one big family. The other, which most authorities use, is to keep the toucans, and split the barbets up until no group contains the toucans within it. The result is 5 families: the toucans, the Asian barbets, the African barbets, the New World barbets, and the toucan-barbets. As a side note, all bird family names end in -idae. The toucans are in Ramphastidae, the New World Barbets Capitonidae, and so on.

Glorified Barbet? Are toucans like this Collared Aracari distinct enough to warrant their own family? It's something of a judgment call. Photo taken by me in Arenal, Costa Rica. 

If it sounds complicated, that's probably why the 4 different checklists of birds of the world that I consulted only agreed on half of the monotypic families. 39 species were placed in their own family by at least one list, but only 20 were on all 4 lists. 6 families were only recognized by 1 list.

The four lists I used were the Clements Checklist (v6.9), the IOC Checklist (v5.1), the Handbook of the Birds of the World (abbreviated HBW), and John Boyd's Taxonomy in Flux List (TiF). The Clements list, currently maintained by the Cornell Lab of Ornithology, is used for eBird and is probably the most well-known list. The IOC list is the product of the International Ornithologist's Union, and the HBW list is produced by Lynx Edicions, a Spanish publisher, and includes full species account for every species. Finally, the TiF list is primarily the work of one man, John Boyd, and is a frequently-updated online taxonomic list that incorporates the most recent studies, with a particular focus on genetic studies. It has fantastic phylogenetic trees of all families, and is definitely worth checking out.

My working spreadsheet shows the wide disparities in passerine classification between the 4 lists

Comparing the 4 lists, the TiF checklist is the least bound by tradition, though it tends towards agreement with the IOC list, and prefers splitting up families: it lists 33 monotypic families. The IOC and Clements lists have 33 and 32, respectively, and there's some degree of agreement between the two. The HBW list, on the other hand, is very conservative, preserving many traditional families and lumping groups together, with the result that it only has 22 monotypic families. The agreement between the four is far greater in the non-passerines, where all have between 16 and 18 families, and the disagreement is not whether a family should be recognized, but whether the group in it is a single species or multiple (Osprey and Ostrich are each considered 1 species by some, and 2 by others). On the other hand, there is huge disparity in the passerines: IOC has 17 monotypic passerine families, and HBW only 6. It is definitely possible that a future edition of the HBW list will dramatically restructure the passerines as the other lists have done, and align more closely with them.

DNA studies have resulted in some radical changes in bird families. This Spotted Elachura, formerly Spotted Wren-babbler, is not at all related to the other wren-babblers. It's the only member of a lineage related to the waxwings. Photo taken in India by Stephen Davis: https://flic.kr/p/eUzoZ7 
Used with permission, all rights reserved by photographer

There are 48 species that are described here: 39 are placed in a monotypic family by at least one of the lists, and the remaining 9 either have historically been considered their own family, or they are a source of disagreement between the lists, and could be placed in their own family in the future. Most of the species are in far-flung parts of the world, so I obviously don't have my own photos for virtually all of them. I'm very grateful to a large number of photographers who have allowed me to use their fantastic photographs. These are either obtained directly from the photographers or via Creative Commons: the permission and license for each photo is listed in the caption. The checklists that recognize each family as monotypic are given in parentheses.

Without further ado, the monotypic bird families of the world!:

Non-Passerines:

Ostrich photo taken by Sharon Davidson in Kenya: https://flic.kr/p/6xhkHY
Used with permission, all rights reserved by photographer

Struthionidae: Ostrich (Clements)-- The largest bird in the world, and one of the most iconic. These huge flightless birds are native to African savannas, though they once ranged into the Middle East. They can run over 40 miles per hour, and males are between 7 and 9 feet tall (females are somewhat smaller, but still huge). They are generally herbivores, but will also eat insects. All four lists agreed that they are distinct enough to merit their own family, but only Clements considered it a monotypic family: the other three split the species in two, recognizing both the Common Ostrich and Somali Ostrich (from of Horn of Africa) as full species.

Emu photo by Sandy Carroll: https://flic.kr/p/4H6dn7
Used with permission, all rights reserved by photographer

Dromaiidae: Emu (TiF, Clements, IOC)-- Another member of the ratites, a group of flightless birds that includes the Ostrich, Kiwis, Cassowaries, and possibly the flying Tinamous. The second-largest bird in the world, growing over six feet tall. They are native to Australia, and like Ostriches have a plant-and-insect diet. Emus that used to exist on King Island and Kangaroo Island are considered by some to have been separate species, but are now extinct. This family is recognized by three of the lists, but placed by the HBW with the Cassowaries in Casuariidae.

Taken in Australia by Wayne Butterworth: https://flic.kr/p/fjsq7z
Used under Creative Commons, some rights reserved by photographer

Anseranatidae: Magpie Goose (All)-- A fairly newly recognized family, this species represents an early branch off of the waterfowl lineage: it diverged after screamers branched off, but before any of the other geese, swans, or ducks. This is a black-and-white goose-like bird native to Northern Australia and Southern New Guinea. It lives in wetlands, but is more terrestrial than other waterfowl and has only partially webbed feet.

Taken by David Ringer in New Caledonia: https://flic.kr/p/4VjrpS
Used under Creative Commons, some rights reserved by photographer

Rhynochetidae: Kagu (All)-- A strange and striking bird, this species is found only on the island of New Caledonia, east of Indonesia, and resembles no other living birds. It's a ghostly pale gray, has long red legs, and stands around two feet tall, with a long crest and a bold striped wing pattern. They are ground-dwelling and carnivorous, and eat snails, worms, and lizards. Research suggests that its closest relative is probably the next species, the similarly enigmatic Sunbittern. A very recent study points to the tropicbirds as the next closest living relatives of these two. This may also be my "most-wanted" bird in the world.

Taken in Costa Rica by Jeff Dyck: https://flic.kr/p/dWRNGg
Used with permission, all rights reserved by photographer

Eurypygidae: Sunbittern (All)-- A fascinating wading-bird-like species from Central and South America. They are cryptically colored but with a brilliant "sunburst" pattern on their spread wings. Generally found near forest streams, where it feeds on aquatic animals. This and the Kagu are very likely most closely related to each other, but may also be related to the odd mesites of Madagascar, rails, cranes, or tropicbirds. 

Oilbird photo taken by Judd Patterson in Trinidad: https://flic.kr/p/7KonY4
Used with permission, all rights reserved by photographer

Steatornithidae: Oilbird (All)-- The bird that thinks it's a bat: convergent evolution has produced a nocturnal, cave-dwelling, fruit-eating bird that uses echolocation to navigate! Native to South America, it is mostly closely related to the potoos, frogmouths, and nightjars, other odd nocturnal birds, but this is the oddest. It gets its name because historically chicks were hunted to make lamp and cooking oil. They are probably most commonly seen at Asa Wright Nature Center in Trinidad, where there is an easily accessible colony. They have been recorded as vagrants as far north as Costa Rica. 

Taken in Ecuador by David Cook: https://flic.kr/p/5c6TYF
Used under Creative Commons, some rights reserved by photographer

Opisthocomidae: Hoatzin (All)-- A very dinosaur-looking bird, large and with a shaggy reddish crest, rufous-and-black wings, and a long tail. Chicks clamber through trees with claws on their wings. It is native to South America, and is generally found in trees by water. They eat leaves, which are digested through fermentation by bacteria in their large crop, giving them a foul smell and the nickname "stinkbird." Even on this list of unusual species it is an oddity: its closest relatives are totally unclear. A number of taxonomic positions have been hypothesized but none proven, and it currently occupies not just a monotypic family but a whole monotypic order.

Photo taken by me! Lake Toho, Florida

Aramidae: Limpkin (All)-- A brown, snail-eating wading bird found in Florida, the Caribbean, and Central and South America. Its vocalization is a screaming cry. It is related to cranes and rails, but distinct enough to be placed in its own family, one of the few families on this list that I have seen, in Florida and Mexico.

Hamerkop photo taken by Tarique Sani in Tanzania: https://flic.kr/p/84QLtp
Used under Creative Commons, some rights reserved by photographer

Scopidae: Hamerkop (All)-- A smallish brown wading bird with a crest that gives it a hammer-shaped head and its name, 'hammerhead' in Afrikaans. Found through much of sub-Saharan Africa, as well as Madagascar, Southwest Saudi Arabia, and Yemen. They constantly build and live in huge stick nests, making as many as five a year. After they are abandoned these nests are often over by other species, including snakes, small mammals, and other birds. Like the next species, they are relatives of the pelicans.

Shoebill photo taken by Bart Wursten in Uganda: https://flic.kr/p/fhxC6x
Used with permission, all rights reserved by photographer

Baleanicipitidae: Shoebill (All)-- Another unique African wading bird, this large gray stork-like bird is named for its giant bill, which is in fact shoe-shaped. It lives in swamps in East Africa, and eats mostly fish, with a particular preference for lungfish, but has been recorded eating a wide variety of aquatic animals. Like the Hamerkop, they are now considered to be closely related to pelicans.

Juvenile Magellanic Plover, photo taken in Argentina by Graham Ekins: https://flic.kr/p/ack71S
Used with permission, all rights reserved by photographer

Pluvianellidae: Magellanic Plover (All)-- This shorebird is found only in southern South America, in Argentina and Chile. While it looks somewhat like a plover, albeit a pale, fat, red-eyed one, it is actually more closely related to the sheathbills in a South polar branch of the larger shorebird group. It's behavior is much like that of a turnstone or plover, but unlike them it feeds its young with food from its crop.

Taken by Allan Hopkins in the Gambia: https://flic.kr/p/nh7jYM
Used under Creative Commons, some rights reserved by photographer

Pluvianidae: Egyptian Plover (All)-- Another "plover" that isn't actually a plover. This is a boldly patterned bird, with gray wings, orange-tinged underparts, and black and white head stripes. Its range is a band across Africa roughly between the Sahara and the equator, where it is found on large rivers. Despite its name, it is not often seen in Egypt. Birders often track it down in the tiny West African nation of the Gambia, on the river of the same name, or in neighboring Senegal. It is often called the "crocodile bird" for supposedly cleaning the teeth of crocodiles in a symbiotic relationship, but this may be a legend.

Ibisbill photo taken in NE India by Mohanram Kemparaju: https://flic.kr/p/4DGDrV
Used with permission, all rights reserved by photographer

Ibidorhynchidae: Ibisbill (All)-- Of the five monotypic shorebird families, this is probably the most impressive bird. Found on high-elevation rocky riverbanks in Central Asia, from Kazakhstan south to India and east through China. It has a black necklace and mask, but its most distinctive feature is the eponymous bill, which is long, decurved, and blood red.

Plains Wanderer photo taken by Julian Teh in New South Wales: https://flic.kr/p/oLuF7d
Used with permission, all rights reserved by photographer

Pedionomidae: Plains-wanderer (All)-- This quail-like shorebird relative is endangered: it is only found in scattered parts of Australia, mostly in the Riverina region of New South Wales. The population size fluctuates but is never thought to be more than 10,000 individuals. As the name suggests, they inhabit grasslands, and are extremely shy: most efforts to spot them are at night, when they are more likely to be in the open. Like some other shorebirds (phalaropes, jacanas, and painted-snipes), sex roles are reversed: the females are more brightly colored, and the males incubate the eggs.

A group of Crab-plovers in Tanzania, photo by Riaan Marais. https://flic.kr/p/bCDWTV
Used with permission, all rights reserved by photographer

Dromadidae: Crab-plover (All)-- Called a plover, and resembles an avocet, but is actually probably closer to the coursers. Its distinctive thick black bill is unique, however. It eats crabs (obviously) on Indian Oceans coastlines from Africa through the Arabian peninsula to India. It nests in burrows in large colonies. Interestingly, the sun heats the burrows to the point where the eggs do not have to be constantly incubated. Also unusual for shorebirds, the young cannot walk when they hatch, and require more parental care than other shorebirds.

Secretarybird photographed in Kenya by Steve Garvie: https://flic.kr/p/k49gkY
Used under Creative Commons, some rights reserved by photographer

Sagittariidae: Secretarybird (All)-- One of the more charismatic species on this list, this large bird of prey resembles a hawk on stilts, standing up to four feet tall. The very long legs protect it from the bites of the snakes (and other small to medium-sized vertebrates) that it hunts on the savannas of Sub-Saharan Africa. They are long-tailed, gray-and-black plumaged, and have a long crest. This is often cited as the inspiration for the name: it looks as if it has quill pens tucked behind its ears. It could also be a corruption of the arabic for "hunter bird": saqr-et-tair.

Osprey photo from Florida, taken by Judd Patterson (www.birdsinfocus.com):
https://flic.kr/p/ahBi2B: Used with permission, all rights reserved by photographer

Pandionidae: Osprey (TiF, Clements, HBW)-- The most widespread and familiar of the birds on this list, the Osprey is now considered to be distinct enough from hawks and eagles to get its own family. It is a large fish-eating bird of prey found on every continent except Antarctica, and is known for its blackish-and-white plumage, crooked-winged flight, and spectacular talons-first fishing dives. The IOC splits the Eastern Osprey of Indonesia and Australia as a full species, so on that checklist this is not a monotypic family.

Taken by David Cook in Madagascar: https://flic.kr/p/dJKZr3
Used under Creative Commons, some rights reserved by photographer

Leptosomidae: Cuckoo Roller (All)-- Unusual and distinct enough to be placed not just in a monotypic family but by many in a monotypic order, and therefore has no close living relatives. The correct taxonomic position is probably somewhere near the grouping that includes woodpeckers and barbets, the hornbills and hoopoes, and the kingfisher/roller/bee-eater order. It's sexually dimorphic, with gray and glossy greenish males and brownish females. It is not a true roller, but like them hunts small prey in sallies from a perch. It is found on only Madagascar and the Comoros.

Passerines:

Sapayoa photo taken in Panama by Nick Athanas (Antpitta.com)
Used with permission, all rights reserved by photographer

Sapayoidae: Sapayoa (Broad-billed Sapayoa) (Clements, TiF)-- Long a source of confusion for taxonomists, the species name is aenigma, referring to its enigmatic taxonomic affinities. It is found in Panama, Colombia, and Ecuador, but seems to be most closely related to the broadbills of the Old World. This would make it the only New World member of a suboscine lineage that includes the broadbills, asities, and pittas. Visually it is relatively drab, a fairly small olive-green forest-dweller with a red eye. Clements and TiF place it in its own family close to the broadbills, but IOC places it an expanded version of the broadbill family, Eurylaimidae, that also includes the asities of Madagascar. HBW keeps it in its traditional placement as a member of the Pipridae, the manakins.

Sharpbill Photo taken in Brazil by Joao Quental: https://flic.kr/p/nXu3dB
Used with permission, all rights reserved by photographer

Oxyruncidae: Sharpbill (Clements, TiF)-- Another greenish neotropical bird with uncertain evolutionary history. Spotted underneath, greenish above, with a pointed (some would say sharp) bill. It is primarily a fruit-eater, and has a patchy distribution in Central and South America. Clements and TiF also give this its own family, but the IOC list considers it a member of a reworked Tityridae family that includes the tityras, becards, and the Royal Flycatcher and other species previous considered tyrant flycatchers. HBW places it with the Cotingas in Cotingidae.

Many-colored Rush Tyrant photo taken by Claudio Dias Timm: https://flic.kr/p/9C5XfK
Used under Creative Commons, some rights reserved by photographer

Tachurididae: Many-colored Rush Tyrant (TiF)-- The first real curveball on this list. This very pretty flycatcher is put in a monotypic family on the TiF list, which reworks and breaks up the traditional Tyrannidae family, creating a number of smaller families. The other three lists keep it in Tyrannidae. It is uncharacteristically brightly-colored for a flycatcher, patterned in green, yellow, blue, red, white and black. It is usually found in reeds near water or marshes, hence the "rush" portion of the name. It is found in South America, North to Peru.

Taken in Enga Province, New Guinea by Erik Enbody: https://flic.kr/p/oL1qeR
Used with permission, all rights reserved by photographer

Eulacestomidae: Wattled Ploughbill (Wattled Shrike-tit) (TiF, IOC)-- A rare species endemic to the mountains of New Guinea. Olive-green and black with a stout bill, the most remarkable feature are the large pink wattles on the males. It apparently gets its name because it uses its bill as a plough when foraging on bark and dead branches. TiF and IOC put it an a separate family, Clements and HBW list it as an early offshoot of the whistler family, Pachyecephalidae.

Mottled Whistler photo taken by Katerina Tvardikova in New Guinea: PNG Birds
Used under Creative Commons, some rights reserved by photographer

Rhagologidae: Mottled Whistler (IOC)-- A little-known berry-eating bird also found only on New Guinea. Mottled greenish, brown, and gray. Its relatives are unclear: the IOC list places it in a monotypic family, TiF puts it as an early branch in the Artamidae, the woodswallows and butcherbirds. Clements lists it as incertae sedis--uncertain placement--near the whistlers. HBW puts it in Pachyecephalidae, the whistlers. As far as I can tell, there are only a handful of photos of a two individuals of this species online.

Bornean Bristlehead photo from Sabah, Borneo, by Alphons Loinsang:  https://flic.kr/p/8LZYKR
Used with permission, all rights reserved by photographer

Pityriaseidae: Bornean Bristlehead (All)-- A spectacular Borneo endemic, probably the most sought-after of a number of amazing birds on the island. Large, mostly black, with a vivid red head, bald yellow crown, and big hooked bill. A social forest-dwelling herbivore. It has been placed in a number of families, but it now usually given its own.

Ifrita photo taken by Katerina Tvardikova in New Guinea: PNG Birds
Used under Creative Commons, some rights reserved by photographer

Ifritidae: Blue-capped Ifrita (Blue-capped Ifrit) (TiF, IOC)-- Yet another New Guinea endemic, this species is best known for being one of a small number of poisonous birds (along with the pitohuis and the Little Shrikethrush). It acquires batrachotoxin from the beetles that it eats, and concentrates the toxin in its feathers. The crown is a brilliant sky blue on an otherwise brownish bird, and it catches insects by creeping along tree branches. This is another species with ambiguous relatives: Clements puts it with the monarch flycatchers in Monarchidae, while HBW puts it in Eupetidae, a large group on that list that contains the rail-babbler, jewel-babblers, and a number of other Australasian groups, and TiF and IOC place it in this monotypic family.

Taken by J. Graham on Tiritiri, New Zealand: https://flic.kr/p/5AGEyp
Used under Creative Commons, some rights reserved by photographer

Notiomystidae: Stitchbird (All)-- A rare New Zealand bird endemic to the North Island and small islands offshore. It was extirpated from all but the tiny Little Barrier Island, but reintroductions have created additional populations. Males are black, yellow, and grey with a white ear tuft, while females are drabber. It feeds on nectar, and was previously thought to be related to the honeyeaters (Meliphagidae) but is now recognized as closer to the New Zealand wattlebirds (Callaeidae).

Taken in Thailand by Francesco Veronesi: https://flic.kr/p/nHF7RV
Used under Creative Commons, some rights reserved by photographer

Eupetidae: Rail-babbler (Malaysian Rail-babbler) (TiF, Clements, IOC)-- An odd ground-dwelling bird with a red, orange, black and white face pattern. It is native to the Malay peninsula, Borneo, and Sumatra. It is secretive and forages for invertebrates while walking along the forest floor like a rail. It is placed in a monotypic family by the TiF, Clements, and IOC lists, and considered closest to two small and anomalous African groups: the rockfowl and rockjumpers. HBW, on the other hand, lumps it in a family with multiple small Australasian groups: the jewel-babblers, quail-thrushes, whipbirds, wedgebills, melampittas, and Ifrita. This larger family retains the name Eupetidae.

Taken by Kev Chapman in the UK: https://flic.kr/p/9Fhpo6
Used under Creative Commons, some rights reserved by photographer

Panuridae: Bearded Reedling (Bearded Tit, Bearded Parrotbill) (TiF, Clements, IOC)-- A small, long-tailed bird found throughout Europe and Asia in reedbeds. Males are gray-headed, with tawny and white bodies and black triangular "beards", females are browner. It was once thought to be a tit, then a parrotbill. HBW preserves the latter classification, calling it the "Bearded Parrotbill" and placing it with them in Paradoxornithidae.

Donacobius photo taken by Claudio Dias Timm: https://flic.kr/p/dTsYvG
Used under Creative Commons, some rights reserved by photographer

Donacobiidae: Donacobius (Black-capped Donacobius) (TiF, Clements, IOC)-- A loud and social species found in wetland habitats throughout South American and into Panama. Black above, tan below, it was once considered a thrush or a mimid, the "Black-capped Mockingthrush." It is now usually thought to be the sole New World representative of an Old World lineage, closest to the grassbirds in Locustellidae. Until recently it was considered a aberrant wren, and HBW still places it with them, in Troglodytidae. 

Taken in Uzbekistan by Francesco Veronesi: https://flic.kr/p/eKtAiv
Used under Creative Commons, some rights reserved by photographer

Scotocercidae: Streaked Scrub-warbler (Scrub Warbler) (IOC)-- Another species not traditionally recognized as particularly distinct, this long-tailed desert denizen is found through North Africa and the Middle East. The other checklists place it in different groups of brown warbler-like Old World birds: TiF and Clements in Cettiidae, and HBW in Cisticolidae. The IOC list recognizes it as sufficiently removed from them to warrant placement in a new family.

Taken in Bhutan by Jon Irvine: https://flic.kr/p/nSUKSR
Used with permission, all rights reserved by photographer

Elachuridae: Spotted Elachura (Spotted Wren-babbler) (TiF, Clements, IOC)-- Surprising molecular studies found that this species, which once was not even afforded its own genus, is in fact a very distinct lineage that deserves placement in a monotypic family. This family is believed to be related to the waxwings and their relatives, as are the next 3 families. It takes the name Elachura to distinguish it from the Wren-babblers it was previously classified with. This is a little-known forest species, brown with indistinct white spotting, that is more often heard than seen. It is found in Southeast Asia from the Himalayas to Southeast China.

Palmchat photo taken in the Dominican Republic by Carlos de Soto Molinari: https://flic.kr/p/jNA2NA
Used under Creative Commons, some rights reserved by photographer

Dulidae: Palmchat (All)-- A common, loud, and social bird endemic to the island of Hispaniola, this is the national bird of the Dominican Republic. They are communal nesters in palms, and also will eat palm fruit, as well as other fruits and flowers. They are also waxwing relatives, but are streaked brown instead of smooth-plumaged like the waxwings.

Hypocolius photo taken in India by Balaji Venkatesh Sivaramakrishnan: https://flic.kr/p/dH9ppX
Used under Creative Commons, some rights reserved by photographer

Hypocoliidae: Hypocolius (Grey Hypocolius) (Clements, IOC, HBW)-- A sleek gray-plumaged bird thought to be related to the waxwings. Males have a striking black mask and white wing tips. They forage for fruit in flocks in the Middle East, from Iraq and the Arabian Peninsula to India. It is generally considered to be in a monotypic family, but the TiF list, in one of its few instances of lumping families, places the next species, also an enigmatic waxwing relative, in the same family.

Photo taken by John C. Mittermeier in Sulawesi, Indonesia: https://flic.kr/p/nFkX6z
Used with permission, all rights reserved by photographer

Hylocitreidae: Hylocitrea (Yellow-flanked Whistler) (Clements, IOC)-- Little-known and endemic to mountain forests on the island of Sulawesi in Indonesia, this species was long considered to be a whistler, the Yellow-flanked Whistler, in the family Pachyecephalidae. HBW retains both that name and classification, while TiF considers it a member of the Hypocoliidae, which superficially it only resembles in that their names start with "hy." They are now both agreed to be members of the waxwing group. It's gray, brown, and olive, with a red eye and a hooked bill tip.

Wallcreeper photographed in Italy by Francesco Veronesi: https://flic.kr/p/6Co9oD
Used under Creative Commons, some rights reserved by photographer

Tichodromidae: Wallcreeper (All)-- A striking mountain specialist ranging throughout Eurasia at high elevations from Northern Spain to Northeastern China. It gets its name from its characteristic behavior of climbing, like a nuthatch or treecreeper, on sheer rocky cliffs, where it also nests in crevices. They are thought to be closely related to the nuthatches, but given a distinct family by most sources. The most striking feature other than the behavior are the bright pink patches on the wings of this otherwise gray species. A personal nemesis bird after a tough miss in the Picos de Europa in Spain.

Taken in China by Paul Jones: https://flic.kr/p/oeqr81
Used with permission, all rights reserved by photographer

Urocynchramidae: Przevalski's Finch (Przevalski's Rosefinch, Pink-tailed Rosefinch, Pink-tailed Bunting) (TiF, Clements, IOC)-- A finch-like brown and pinkish species endemic to mountains in West-central China. Variously considered a finch or a bunting, but now widely considered to neither: it represents the only member of its own unique group. HBW continues to place it with the finches in Fringillidae, but acknowledges its taxonomic uncertainty. There is little information about this species, but it is thin-billed and long-tailed and is known to eat seeds in high-elevation habitats in its restricted range. How it is pronounced? Apparently it's pshuh-val-skee's, or even just shuh-val-skee's: the name commemorates Russian explorer Nikolay Przhevalsky, whose name can be transliterated in a lot of different ways, and who is also honored in the name of the only surviving wild horse species, the Przewalski's Horse. Notice that the name has been spelled 3 different ways now: those seem to be the most common spellings in each case. All are apparently acceptable English versions of the name Пржева́льский. 

Olive Warbler by Ron Knight, Taken in Mexico: https://flic.kr/p/diX1E7
Used under Creative Commons, some rights reserved by photographer

Peucedramidae: Olive Warbler (All)-- One of the few monotypic families found in the ABA area (and consequently one of the few I've seen), this small passerine resembles and behaves like a wood-warbler but diverged much earlier and represents its own family, potentially related to the accentors. Despite its name, males are gray with a black mask and orange-ish hood, while females are drabber with a yellowish hood. Found in montane coniferous forests from Arizona and New Mexico south through Mexico and Central America to Nicaragua.

Thrush-Tanager photo taken by Rebecca Houseman in Panama: https://flic.kr/p/4wKN76
Used with permission, all rights reserved by photographer

Rhodinocichlidae: Rosy Thrush-Tanager (TiF)-- Usually considered a tanager (and placed in Thraupidae by 3 of the lists), this colorful red, black and white bird has a patchy and disjunct range in Mexico, Costa Rica and Panama, Colombia, and Venezuela. Despite being brightly colored, it can be hard to see in tropical forest undergrowth or while foraging on the ground. It has historically been considered not just a tanager but also an ovenbird, a wren, a mimid, or a warbler, and TiF tentatively identifies it as in its own family outside of the tanager/cardinal/sparrow/wood-warbler/blackbird radiation.

Photo by me! Taken in Monteverde, Costa Rica

Coerebidae: Bananaquit (IOC)-- A widespread and often abundant nectar-eater of the New World tropics, from Mexico and the Caribbean (and rarely Florida) south to Uruguay. It is quite variable, with 41(!) named subspecies, but all are a combination of black, grey, olive, and yellow, with a white eyebrow. It is adaptable and common in gardens and other human-modified habitats. While it is sometimes put in a monotypic family, including on the IOC list, many authorities consider it to be a tanager: TiF, Clements and HBW all place it in Thraupidae.

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So that's them: 39 birds listed as monotypic families by at least one of the four authorities. But taxonomy is always changing, and there are a number of species that have been considered monotypic families in the past, or whose taxonomic placement is uncertain. I've added accounts for 12 of these. There's a lot of "incertae sedis" (uncertain placement) in this group. A note on the HBW-- in many cases that list seems to be slow to make changes based on new molecular studies, and will probably change its classification eventually in the cases where it disagrees with the 3 other lists.

It's quite possible that some of these species will eventually be given their own family, or at least end up somewhere different from where they are now. It is worth noting that this isn't all of the birds whose taxonomic placement is uncertain: only those that are both uncertain and not closely related to others, so that they are potentially candidates for a monotypic family. Feel free to comment if you think anything else should be described here.

Hoopoe(s)-- This striking crested bird from throughout Eurasia and Africa was long considered to be a monotypic family, Upupidae. That family still exists, but it is no longer monotypic: the Hoopoe has been split into 2 or more species. In addition to the familiar Eurasian Hoopoe, TiF and IOC recognize 2 more extant species, the African Hoopoe and Madagascan Hoopoe, as well as the extinct St. Helena Hoopoe. Clements and HBW recognize only 1 additional species, the Madagascar Hoopoe (note the different spelling). The woodhoopoes are in a separate family, Phoeniculidae.

Kinglet Calyptura-- An incredibly rare bird endemic to Atlantic forests in Southeastern Brazil. It is tiny, short-tailed, with a kinglet-like red crown. It had not been seen in over 100 years when it was rediscovered in 1996. There have been no confirmed reports since then, though there have been unconfirmed reports. It is considered critically endangered, because assuming there is still a surviving population it is likely under 50 individuals. There do not seem to be any photos of this bird alive. It's also a taxonomic enigma, being placed with the cotingas, tityras, or tyrant flycatchers. HBW and Clements put it in Cotingidae, while IOC places it with the flycatchers in Tyrannidae. TiF also considers it a flycatcher, but in with the spadebills in a small family split off of the main Tyrannidae, called Platyrinchidae: this placement is based on a recent DNA study.

Silktail-- This striking Fiji endemic looks like a tiny bird-of-paradise but was usually classified as a monarch flycatcher. Small and black, with blue iridescence on the head of the male and a white rump and tail. It is now considered (though HBW still calls it a monarch) to be basal in the fantail family, Rhipiduridae, and its closest relative is the next species, which also was of unclear affinities but placed in a completely different family.

Pygmy Drongo (Pygmy Drongo-Fantail)-- A New Guinea endemic which thought to be an aberrant drongo in Dicruridae (HBW retains this), but which has the wrong number of primary feathers. Small, black, superficially drongo-like, and poorly known, it is now recognized as the sister species of the similarly enigmatic Silktail of Fiji. Together they are basal in the Rhipiduridae, the Fantails.

Yellow-bellied Fairy-Fantail (Yellow-bellied Fantail, Yellow-bellied Flycatcher?)- Unlike the previous two species, this bird moved out of, not into the Rhipiduridae, where HBW places it. It is more closely related to a group of Old Warbler flycatcher-like species, including the species called Fairy Flycatcher, that are collectively now placed in the Fairy Flycatcher family, Stenostiridae. This brightly patterned gray and yellow bird is found in South Asia from Pakistan through the Himalayas and South to Thailand and Vietnam. The common name is the source of some dispute: while Clements, TiF, and IOC agree on the family, they all give different names. Clements calls it the Yellow-bellied Fairy-Fantail, acknowledging both its current and former placement. IOC retains the Yellow-bellied Fantail name, which could be confusing given that it is not a fantail. Even more confusing is the TiF 
suggestion of Yellow-bellied Flycatcher, which would conflict with the North American Empidonax flycatcher of the same name. The obvious choice to me would be Yellow-bellied Fairy-Flycatcher, but no list uses that name. 

Crested Jay-- The name makes it seem straightforward enough, but this Southeast Asian species found on the Malay Peninsula and the western part of Indonesia is not a typical jay. It is dark brown with a very tall crest and a white blotch on each side of the head. It isn't closely related to the other jays, but Clements, IOC, and HBW still place it with them in Corvidae. The IOC list acknowledges that this is probably outdated, and the TiF list calls it an early (basal) offshoot of the Shrikes and puts it in Laniidae.

Grauer's Warbler-- Not to be confused with Grauer's Swamp Warbler, this drab Central African species is found along the Rift Valley in Burundi, Rwanda, Uganda, and the DRC. Its taxonomic placement is probably somewhere within the mess that used to be the Old World Warblers, but it is relatively distinct and it isn't clear exactly where. Both TiF and Clements put it with the Macrosphenidae, the African Warblers: the former has it as basal in the family, while the latter puts it as incertae sedis at the end. The IOC list gives up entirely and just calls it incertae sedis, while the HBW list puts it in the larger warbler group Sylviidae but acknowledges the confusion.

Cinnamon Ibon-- A rufous canopy-dwelling bird endemic to mountains on Mindanao, in the Philippines. It was once considered an odd member of the white-eye family Zosteropidae, where HBW still places it (though notes that this may be incorrect). Surprisingly, mtDNA studies have found that it is the early offshoot of the Old World Sparrows, a group that includes the familiar House Sparrow. As a result TiF, Clements, and IOC put in that family, Passeridae.

São Tomé Short-tail (Bocage's Longbill)-- Another enigmatic island species whose relationships are now thought to be resolved. It used to be (and on the HBW list still is) in Sylviidae. The other lists now consider it to be closer to the pipits, and place it in Motacillidae. It is rare and only found on São Tomé, off the coast of West Africa. It is a rather drab brown and gray forest floor bird.

Wrenthrush (Zeledonia)-- An elusive and unique bird found only in the mountains of Costa Rica and Panama. Short-tailed and round, this gray bird has a striking orange crown. It forages on the ground, but despite its name is neither a wren nor a thrush. It is probably either its own family or a wood-warbler (Parulidae): Clements and HBW go with the latter, while IOC and TiF play it safe and characterize it as incertae sedis for the time being. Of these twelve, this is probably the most likely to end up as a monotypic family.

Yellow-breasted Chat-- I first learned to identify this species, the oddball bird of the Eastern US, as a weird wood-warbler. It certainly doesn't resemble the other warblers very much, and alternatives have been suggested but not proven. HBW and Clements call it a warbler, TiF puts it in Icteridae as a New World Blackbird, and IOC calls it incertae sedis.

Plushcap-- A distinctive South American bird found from Venezuela to Bolivia. Rusty and gray with a vivid yellow cap (made up of dense velvety feathers: hence the name), it resembles little else and was until recently given its own family, Catamblyrhynchidae. It is now generally agreed to be a tanager, and placed by all four lists in Thraupidae.

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And that brings us to the end of our list. I had fun (a learned a ton) putting this together, if you've made it this far I hope you enjoyed it. Certainly feel free to comment if I made a mistake, missed a bird, or if you just want to give a shout out to your favorite monotypic bird family (Mine has to be the Kagu or Secretarybird, with Oilbird and Sunbittern close behind). I started this project after pondering whether it would be possible for me to see all of the bird families of the world. The conclusion: it would be tough. I'd have to make stops for monotypic families on the islands of New Caledonia, Sulawesi, Borneo, New Guinea, New Zealand (North Island), Madagascar, and Hispaniola. There are tough-to-find species from this list on every continent except Antarctica (and I'd probably have to go there anyway to see a Sheathbill). But it would also be so much fun, and while I'm not sure that I'll ever be able to see them all, I'd certainly like to get close! New Caledonia here I come! Someday.