Proposed splits for which (full) information is currently lacking to me
At present, these are 194 taxa of which I have heard that they have been or will be proposed to be split, yet either (1) enough details are lacking to include them in the main lists, or (2) I consider the currently available information to me just too little to do so. I cannot guarantee the correctness of the information below. The list is here included as an appetizer and also as a request for further information. It does include a number of taxa that have been split in some field guide for a region, but for which I have no other reference. Species with a trailing '@' character behind their vernacular name are considered extinct.
Puna Rhea Rhea tarapacensis
split from: Rhea pennata
King Island Emu@ Dromaius ater
split from: Dromaius novaehollandiae
Magdalena Tinamou Crypturellus saltuarius
split from: Crypturellus erythropus
Colombian Tinamou Crypturellus columbianus
split from: Crypturellus erythropus
Biak/Geelvink Megapode Megapodius geelvinkianus
split from: Megapodius freycinet
Kirk's Francolin Peliperdix rovuma
split from: Peliperdix sephaena
Malayan Partridge Arborophila campbelli
split from: Arborophila orientalis
Siamese Partridge Arborophila diversa
split from: Arborophila cambodiana
Hainan Peacock-Pheasant Polyplectron katsumatae
split from: Polyplectron bicalcaratum
Malaysian Argus Rheinardia nigrescens
split from: Rheinardia ocellata
Tundra Bean Goose Anser serrirostris
split from: Anser fabalis
Tundra Lesser Canada Goose Branta hutchinsii
split from: Branta canadensis
Andean Teal Anas andium
split from: Anas flavirostris
Crozet Pintail Anas drygalskii
split from: Anas eatoni
Bar-breasted Piculet Picumnus borbae
split from: Picumnus aurifrons
Pará Piculet Picumnus pallidus
split from: Picumnus spilogaster
Arizona Woodpecker Picoides arizonae
split from: Picoides stricklandi
Bronze-winged Woodpecker Piculus aeruginosus
split from: Piculus rubiginosus
Crimson-fronted Barbet Megalaima malabarica
split from: Megalaima rubricapilla
Woodward's Barbet Stactolaema woodwardi
split from: Stactolaema olivacea
Gilded Barbet Capito auratus
split from: Capito niger
Wagler's Emerald-Toucanet Aulacorhynchus wagleri
split from: Aulacorhynchus prasinus
Blue-throated Emerald-Toucanet Aulacorhynchus caeruleogularis
split from: Aulacorhynchus prasinus
"Nelson's" Emerald-Toucanet Aulacorhynchus cognatus
split from: Aulacorhynchus prasinus
Santa Marta Emerald-Toucanet Aulacorhynchus lautus
split from: Aulacorhynchus prasinus
"Northern Andean" Emerald-Toucanet Aulacorhynchus albivitta
split from: Aulacorhynchus prasinus
"Peruvian" Emerald-Toucanet Aulacorhynchus atrogularis
split from: Aulacorhynchus prasinus
Central African Hoopoe Upupa senegalensis
split from: Upupa africana
Madagascar Hoopoe Upupa marginata
split from: Upupa africana
Comoro Cuckoo-Roller Leptosomus gracilis
split from: Leptosomus discolor
Highland Motmot Momotus aequatorialis
split from: Momotus momota
Niau Kingfisher Todiramphus gertrudae
split from: Todiramphus gambieri
Horsfield's Cuckoo Cuculus horsfieldi
split from: Cuculus saturatus
Green-capped Coua Coua olivaceiceps
split from: Coua ruficeps
Papuan Lorikeet Charmosyna stellae
split from: Charmosyna papou
Seychelles Black-Parrot Coracopsis barklyi
split from: Coracopsis nigra
Aztec Parakeet Aratinga astec
split from: Aratinga nana
Grey-rumped Swiftlet Collocalia marginata
split from: Collocalia esculenta
Chillagoe Swiftlet Aerodramus chillagoensis
split from: Aerodramus spodiopygius
Amazonian Swift Chaetura viridipennis
split from: Chaetura chapmani
Tumbes Swift Chaetura ocypetes
split from: Chaetura brachyura
Sick's Swift Chaetura meridionalis
split from: Chaetura andrei
Fernando Po Swift Apus sladeniae
split from: Apus barbatus
Boucard's Hermit Phaethornis saturatus=adolphi
split from: Phaethornis longuemareus/striigularis
Salvin's Emerald Chlorostilbon salvini
split from: Chlorostilbon canivetii
"Elegant" Emerald@ Chlorostilbon elegans
split from: Chlorostilbon bracei
West Andean Emerald Chlorostilbon melanorhynchus
split from: Chlorostilbon gibsoni
Doubleday's Hummingbird Cynanthus doubledayi
split from: Cynanthus latirostris
Emerald-bellied Woodnymph Thalurania hypochlora
split from: Thalurania fannyi
Humboldt's Sapphire Hylocharis humboldtii
split from: Hylocharis grayi
Escudo Hummingbird Amazilia handleyi
split from: Amazilia tzacatl
Cinnamon-sided Hummingbird Amazilia wagneri
split from: Amazilia viridifrons
Purple-throated Mountain-gem Lampornis calolaema
split from: Lampornis castaneoventris
Grey-tailed Mountain-gem Lampornis cinereicauda
split from: Lampornis castaneoventris
Mérida Sunangel Heliangelus spencei
split from: Heliangelus clarisse
Roti Island Hawk-Owl Ninox rotiensis
split from: Ninox novaeseelandiae
Siau Scops-Owl Otus siaoensis
split from: Otus manadensis
Guatemalan Pygmy-Owl Glaucidium cobanense
split from: Glaucidium gnoma
Mexican Whip-poor-will Caprimulgus arizonae
split from: Caprimulgus vociferus
Ringed Turtle-Dove Streptopelia risoria
split from: Streptopelia roseogrisea
Indigo-crowned Quail-Dove Geotrygon purpurata
split from: Geotrygon saphirina
Mindanao Brown-Dove Phapitreron brunneiceps
split from: Phapitreron cinereiceps
Comoro Green-Pigeon Treron griveaudi
split from: Treron australis
Barrow's Bustard Eupodotis barrowii
split from: Eupodotis senegalensis
Ecuadorian Rail Rallus aequatorialis
split from: Rallus limicola
Aldabra Rail Dryolimnas aldabranus
split from: Dryolimnas cuvieri
Wilson's Snipe Gallinago delicata
split from: Gallinago gallinago
Chatham Islands Oystercatcher Haematopus chathamensis
split from: Haematopus unicolor
Thayer's Gull Larus thayeri
split from: Larus glaucoides
Cuban Kite Chondrohierax wilsonii
split from: Chondrohierax uncinatus
Yellow-billed Kite Milvus parasitus/aegyptius
split from: Milvus migrans
Ryukyu Serpent-Eagle Spilornis perplexus
split from: Spilornis cheela
Mentawai Serpent-Eagle Spilornis sipora
split from: Spilornis cheela
Natuna Serpent-Eagle Spilornis natunensis
split from: Spilornis cheela
Bawean Serpent-Eagle Spilornis baweanus
split from: Spilornis cheela
Nias Serpent-Eagle Spilornis asturinus
split from: Spilornis cheela
Simeulue Serpent-Eagle Spilornis abbotti
split from: Spilornis cheela
Madagascar Marsh-Harrier Circus macrosceles
split from: Circus maillardi
American Harrier Circus hudsonius
split from: Circus cyaneus
Variable Goshawk Accipiter hiogaster
split from: Accipiter novaehollandiae
Forest Buzzard Buteo trizonatus
split from: Buteo oreophilus
Eurasian Tawny Eagle Aquila vindhiana
split from: Aquila rapax
Northern Caracara Caracara cheriway
split from: Caracara plancus
Grebe Podiceps navasi
split from: Podiceps major
Crozet Shag Phalacrocorax melanogenis
split from: Phalacrocorax atriceps
Greater Flamingo Phoenicopterus roseus
split from: Phoenicopterus ruber (American Flamingo)
Dwarf Olive Ibis Bostrychia bocagei
split from: Bostrychia olivacea
Greater Snow Petrel Pagodroma confusa
split from: Pagodroma nivea
Herald Petrel Pterodroma heraldica
split from: Pterodroma arminjoniana
Jamaican Petrel Pterodroma caribbaea
split from: Pterodroma hasitata
Newell's Shearwater Puffinus newelli
split from: Puffinus auricularis
Loja Tyrannulet Zimmerius flavidifrons
split from: Zosterops chrysops
"Dull" Yellow-breasted Flycatcher Tolmomyias viridiceps
split from: Tolmomyias flaviventris
Atlantic Royal-Flycatcher Onychorhynchus swainsoni
split from: Onychorhynchus coronatus
Pacific Royal-Flycatcher Onychorhynchus occidentalis
split from: Onychorhynchus coronatus
Yellow-cheeked Becard Pachyramphus xanthogenys
split from: Pachyramphus viridis
Lined Antshrike Thamnophilus tenuepunctatus
split from: Thamnophilus palliatus (Chestnut-backed Antshrike)
"fuscicauda" Blackish Antbird Cercomacra fuscicauda
split from: Cercomacra nigrescens
Royal Cinclodes Cinclodes aricomae
split from: Cinclodes excelsior
Chinchipe Spinetail Synallaxis chinchipensis
split from: Synallaxis stictothorax
Marañón Crescent-chest Melanopareia maranonica
split from: Melanopareia elegans
Ashy Myzomela Myzomela cineracea
split from: Myzomela eques
Large Vireo Vireo gravis
split from: Vireo solitarius
Sympatric Warbling-Vireo Vireo sympatrica
split from: Vireo swainsonii
Victoria Mountains Warbling-Vireo Vireo victoriae
split from: Vireo gilvus
Northern Lemon-chested Greenlet Hylophilus griseiventris
split from: Hylophilus thoracicus
"Himalayan" Jungle-Crow Corvus japonensis
split from: Corvus macrorhynchos??
Green Jay Cyanocorax luxuosus
split from: Cyanocorax yncas
Bornean Treepie Dendrocitta cinerascens
split from: Dendrocitta occipitalis
Black-billed Magpie Pica hudsonia
split from: Pica pica
Comoro Cuckooshrike Coracina cucullata
split from: Coracina cinerea
Spot-breasted Fantail Rhipidura albogularis
split from: Rhipidura albicollis
Solomon Islands Drongo Dicrurus solomonensis
split from: Dicrurus bracteatus
Annobon Paradise-Flycatcher Terpsiphone smithii
split from: Terpsiphone rufiventer
Kauai Elepaio Chasiempis sclateri
split from: Chasiempis sandwichensis
Oahu Elepaio Chasiempis ibidis
split from: Chasiempis sandwichensis
Comoro Blue Vanga Cyanolanius comorensis
split from: Cyanolanius madagascarinus
Amber Mountain Rock-Thrush Pseudocossyphus erythronotus
split from: Pseudocossyphus sharpei
Taita Thrush Turdus helleri
split from: Turdus olivaceus
Somali Thrush Turdus ludoviciae
split from: Turdus olivaceus
Brown-streaked Flycatcher Muscicapa williamsoni
split from: Muscicapa dauurica
Red-throated Flycatcher Ficedula albicilla
split from: Ficedula parva
Atlas Flycatcher Ficedula speculigera
split from: Ficedula hypoleuca
Chinese Flycatcher Ficedula elisae
split from: Ficedula narcissina
Furtive Flycatcher Ficedula disposita
split from: Ficedula crypta
Black Bushchat Saxicola aethiops
split from: Saxicola caprata
Red-tailed Wheatear Oenanthe chrysopygia
split from: Oenanthe xanthoprymna
White-browed Wren Thryothorus albinucha
split from: Thryothorus ludovicianus
Southern House-Wren Troglodytes musculus
split from: Troglodytes aedon
Antillean Wren Troglodytes martinicensis
split from: Troglodytes aedon
White-browed Gnatcatcher Polioptila bilineata
split from: Polioptila plumbea
Cape Titmouse Baeolophus cineraceus
split from: Baeolophus inornatus
Black-browed Tit Aegithalos bonvaloti
split from: Aegithalos iouschistos
Pale Martin Riparia diluta
split from: Riparia riparia
Uluguru Mountain Greenbul Andropadus neumanni
split from:
Pale-crowned Cisticola Cisticola cinnamomeus
split from: Cisticola brunnescens
Swamp Prinia Prinia cinerascens
split from: Prinia burnesii
Saffron-breasted / Drakensberg Prinia Prinia hypoxantha
split from: Prinia maculosa
Taita Apalis Apalis fuscigularis
split from: Apalis thoracica
Namuli Apalis Apalis lynesi
split from: Apalis thoracica
Miombo Wren-Warbler Calamonastes undosus
split from: Calamonastes simplex
Kirk's White-eye Zosterops kirki
split from: Zosterops senegalensis
Kulal White-eye Zosterops kulalensis
split from: Zosterops poliogaster
Taita White-eye Zosterops silvanus
split from: Zosterops poliogaster
South Pare White-eye Zosterops winifredae
split from: Zosterops poliogaster
Cape White-eye Zosterops capensis
split from: Zosterops pallidus
Green White-eye Zosterops virens
split from: Zosterops pallidus
Mauritius Grey White-eye Zosterops mauritianus
split from: Zosterops borbonicus
Two-barred Greenish Warbler Phylloscopus plumbeitarsus
split from: Phylloscopus trochiloides
Large-billed Reed Warbler Acrocephalus orinus
split from: not a real split
Benguet Bush-Warbler Bradypterus seebohmi
split from: Bradypterus mandelli
Javan Bush-Warbler Bradypterus montis
split from: Bradypterus mandelli
Timor Bush-Warbler Bradypterus timoriensis
split from: Bradypterus mandelli
Subdesert Brush-Warbler Nesillas lantzii
split from: Nesillas typica
Moheli Brush-Warbler Nesillas moheliensis
split from: Nesillas typica
Oriental Reed-Warbler Acrocephalus orientalis
split from: Acrocephalus arundinaceus
?? Warbler Seicercus distinctus
split from: Seicercus tephrocephalus
Black-headed Sibia Heterophasia desgodinsi
split from: Heterophasia melanoleuca
??? Parrotbill Paradoxornis polivanovi
split from: Paradoxornis heudei
Damara Clapper Lark Mirafra damarensis
split from: Mirafra apiata
Visayan Flowerpecker Dicaeum haematostictum
split from: Dicaeum australe
Abbott's Sunbird Nectarinia abbotti
split from: Nectarinia sovimanga?
Violet-breasted Sunbird Nectarinia chalcomelas
split from: Nectarinia pembae
Comoro Green Sunbird Nectarinia moebii
split from: Nectarinia notata?
Temminck's Sunbird Aethopyga temminckii
split from: Aethopyga mystacalis
Pacific Water Pipit Anthus japonicus
split from:
Asian Desert Sparrow Passer zarudnyi
split from: Passer simplex
Menzbier's Pipit Anthus menzbieri
split from: Anthus gustavi
Aldabra Fody Foudia aldabrana
split from: Foudia eminentissima
Chestnut-eared Finch Taeniopygia castanotis
split from: Taeniopygia guttata
Thick-billed Fox Sparrow Passerella megarhyncha
split from: Passerella iliaca
Sooty Fox Sparrow Passerella unalaschensis
split from: Passerella iliaca
Slate-coloured Fox Sparrow Passerella schistacea
split from: Passerella iliaca
Baird's Junco Junco bairdi
split from: Junco phaeonotus
Ipswich Sparrow Passerculus princeps
split from: Passerculus sandwichensis
Belding's Sparrow Passerculus beldingi
split from: Passerculus sandwichensis
Sage Sparrow Amphispiza nevadensis
split from: Amphispiza belli
Audubon's Warbler Dendroica auduboni
split from: Dendroica coronata
Barbuda Warbler Dendroica subita
split from: Dendroica adelaidae
St. Lucia Warbler Dendroica ???
split from: Dendroica adelaidae
Choco Warbler Basileuterus chlorophrys
split from: Basileuterus chrysogaster
Chestnut-capped Warbler Basileuterus delattrii
split from: Basileuterus rufifrons
Western Hemispingus Hemispingus ochraceus
split from: Hemispingus melanotis
Olive Tanager Chlorothraupis frenata
split from: Chlorothraupis carmioli
White-bellied Tanager Tangara brasiliensis
split from: Tangara mexicana
Silver-breasted Tanager Tangara cyanomelaena
split from: Tangara velia
Yellow-tufted Dacnis Dacnis egregia
split from: Dacnis lineata
Black Seedeater Sporophila corvina
split from: Sporophila americana
Caquetá Seedeater Sporophila murallae
split from: Sporophila americana
Slate-blue Seedeater Amaurospiza relicta
split from: Amaurospiza concolor
Black-cowled Oriole Icterus prosthemelas
split from: Icterus dominicensis
Pale Cowbird Molothrus fringillarius
split from: Molothrus badius
Bronze-brown Cowbird Molothrus armenti
split from: Molothrus aeneus