The 2021 AOS Supplement is out!

by Michael L. P. Retter

Every summer, birders anxiously await publication of the “Check-list Supplement” by the American Ornithological Society’s Committee on Classification and Nomenclature of North and Middle American Birds (a.k.a. the NACC). The supplement (available here) details revisions to the NACC’s Check-list. Below is a rundown of the more significant revisions. You can read all the proposals on which the NACC voted this year at Later in the year, be sure to check out ABA’s annual “Check-list Redux” in North American Birds magazine. There, you’ll find photos, maps, and more detailed analysis of these changes.

Nowadays, it can be assumed that any change in taxonomy is due (at least partly) to analysis of new genetic data, so that is not always mentioned below. As a general policy, the NACC accepts as additions to its North American Check-list any species the ABA’s Checklist Committee adds to its list. Those changes are not listed here. In instances where new species appear on the Check-list because of a split, the sequence in which they are listed here is the sequence in which they appear on the Check-list. Species marked with single asterisks (*) below are those which do not appear on the ABA Checklist. Those which do not appear on AOS’s North American Check-list are marked with double asterisks (**). Extinct species are marked with daggers (†).

This year, the topics most likely to generate discussion within the ABA Area are probably the split of Mew Gull and a major reshuffle of passerine families. The latter will profoundly alter checklists such as the ABA’s which adhere to taxonomic sequence. There are also new genera for Spruce Grouse, most of our cormorants, Ruby-crowned Kinglet, Java Sparrow, Lavender Waxbill, and (yet again!) Five-striped Sparrow. Crested Caracara has its pre-2000 scientific name back, and a split of Sedge Wren changes the scientific name of the northern, migratory population.

Further south, in Middle America and the West Indies, Cinereous Owl, Grass Wren, Bahama Nuthatch, White-browed Gnatcatcher, Yellow-throated Nightingale-Thrush, Chestnut-capped Warbler, West Mexican Euphonia, and St. Kitts Bullfinch newly appear on the Check-list. In addition, there are new genera for the Central American woodstars, a couple owls, Flammulated Flycatcher, and a handful of euphonias.


Split of Mew Gull

Common Gull (Larus canus)

Short-billed Gull (Larus brachyrhynchus)

This split has been a long time coming, and because of that, ID criteria are well covered in current field guides. All Old-World-breeding subspecies, including “Kamchatka Gull”, are included within Common Gull, making the New-World-breeding Short-billed Gull monotypic.

Hello, Canachites!

Spruce Grouse (Facipennis canadensis Canachites canadensis)

Spruce Grouse is changing genera yet again! It was not so long ago in Dendragapus, so this make the third genus for it in the last 20 years or so.

New Genera for Cormorants

The genus Phalacrocorax has been split. While Great Cormorant remains in that Old World genus, most of our cormorants are now placed in one of two new genera. The suffix in the specific epithets of Double-crested and Neotropic cormorants has also changed.

Brandt’s Cormorant (Phalacrocorax penicillatus Urile penicillatus)

Red-faced Cormorant (Phalacrocorax urile Urile urile)

Pelagic Cormorant (Phalacrocorax pelagicus Urile pelagicus)

Double-crested Cormorant (Phalacrocorax auritus Nannopterum auritum)

Neotropic Cormorant (Phalacrocorax brasilianus Nannopterum brasilianum)

Lump of Crested and Southern caracaras

Crested Caracara (Caracara cheriway Caracara plancus)

Southern Caracara Crested Caracara (Caracara plancus)**

This is a reversal of a 20-year-old action that saw Crested and Southern caracaras split. Some of us may remember that at the time it resulted in the first edition of the Sibley guide featuring one of two English names that never existed (Northern Caracara and American Magpie)! The two species meet and hybridize in South America. The main visual difference between them is that Southern Caracara has more extensive pale barring on the mantle. In the ABA Area, this action effectively results in a scientific name change for Crested Caracara.

Hello, Corthylio!

Ruby-crowned Kinglet (Regulus calendula Corthylio calendula)

As anyone who has seen members the genus Regulus in the Old World will tell you, Golden-crowned Kinglets are very similar to them, and Ruby-crowned Kinglets are very different—so different, in fact, they now get their own genus, Corthylio. In addition, Ruby-crowned now appears before Golden-crowned in the checklist sequence.

Split of Sedge Wren

(Cistothorus stellaris) Sedge Wren

(Cistothorus platensis) Grass Wren*

The non-migratory Neotropical populations of Sedge Wren are now treated as a different species. In the ABA Area, this effectively changes the scientific name of Sedge Wren. Grass Wren is resident from central Mexico south to South America.

Split of Eurasian Blackbird

Eurasian Blackbird (Turdus merula)

Tibetan Blackbird (Turdus maximus)**

Chinese Blackbird (Turdus mandarinus)**

Indian Blackbird (Turdus simillimus)**

This four-way split (unsurprisingly) affects populations in the Old World.

Hello, Amphispizopsis!

Five-striped Sparrow (Amphispiza quinquestriata Amphispizopsis quinquestriata)

The poor Five-striped Sparrow just can’t seem to find a home. It has moved genera so many times in the past 20 years it’s hard to keep track. Genetic data seem to indicate it deserves its own genus rather than being shacked up in Amphisipza with Black-throated Sparrow.

Hello, Padda!

Java Sparrow (Lonchura oryzivora Padda oryzivora)

Padda was absorbed into Lonchura in 2004, but it’s back! Java Sparrow is an Asian species established in Hawaii.

Hello, Glaucestrilda!

Lavender Waxbill (Estrilda caerulescens Glaucestrilda caerulescens)*

This is an African species with a presence in Hawaii. It’s on the AOS Checklist but not the ABA Checklist.

English name modification for Helopsaltes ochotensis

Middendorff’s Grasshopper-Warbler ➛ Middendorff’s Grasshopper Warbler

Major Passerine Family Reshuffle

The sequence of the passerines has one again been shuffled. With hope, consensus about older portions of the avian evolutionary tree will minimize such upheavals in the future. The new sequence is as follows:

Sapayoidae* (sapayoas)

Pipridae* (manakins)

Cotingidae* (cotingas)

Tityridae (tityras and becards)

Oxyruncidae* (sharpbills)

Onychorhynchidae* (royal flycatchers)

Tyrannidae (tyrant flycatchers)

Conopophagidae* (gnateaters and gnatpittas)

Thamnophilidae* (true antbirds)

Grallariidae* (true antpittas)

Rhinocryptidae* (tapaculos)

Formicariidae* (antthrushes)

Furnariidae* (furnariids, incl. woodcreepers)

Vireonidae (vireos)

Monarchidae (monarch flycatchers)

Laniidae (shrikes)

Corvidae (corvids)

Remizidae (penduline tits)

Paridae (tits)

Alaudidae (larks)

Acrocephalidae (reed warblers)

Donacobiidae* (donacobiuses)

Locustellidae (grasshopper warblers)

Hirundinidae (swallows)

Aegithalidae (bushtits)

Cettidae (bush warblers)

Phylloscopidae (leaf warblers)

Pycnonotidae (bulbuls)

Sylviidae (true warblers)

Zosteropidae (white-eyes)

Leiothrichidae (laughingthrushes)

Regulidae (kinglets)

Dulidae* (palmchats)

Bombycillidae (waxwings)

Ptiliogonatidae (silky-flycatchers)

Mohoidae (‘o‘os)

Sittidae (nuthatches)

Certhiidae (treecreepers)

Polioptilidae (gnatcatchers and gnatwrens)

Troglodytidae (wrens)

Mimidae (mimids)

Sturnidae (starlings and mynas)

Cinclidae (dippers)

Turdidae (thrushes)

Muscicapidae (chats)

Peucedramidae (ocoteros)

Ploceidae (weavers)

Viduidae* (whydahs)

Estrildidae (waxbills)

Prunellidae (accentors)

Passeridae (Old World sparrows)

Motacillidae (pipits and wagtails)

Fringillidae (true finches)

Rhodinocichlidae* (thrush-tanagers)

Calcariidae (longspurs and snow buntings)

Emberizidae (true buntings)

Passerellidae (New World sparrows)

Calyptophilidae* (chat-tanagers)

Zeledoniidae* (wrenthrushes)

Phaenicophilidae* (Hispaniolan tanagers)

Nesospingidae* (Puerto Rican tanagers)

Spindalidae (spindalises)

Teretistridae* (Cuban warblers)

Icteriidae (yellow-breasted chats)

Icteridae (icterids)

Parulidae (New World warblers)

Cardinalidae (cardinalids)

Mitrospingidae* (mitrospingid tanagers)

Thraupidae (true tanagers)

Change in sequence for Chaetura swifts

The new sequence is as follows:

Gray-rumped Swift*

Band-rumped Swift*

Costa Rican Swift*

Lesser Antillean Swift*

Chimney Swift

Vaux’s Swift

Chapman’s Swift*

Sick’s Swift*

Short-tailed Swift*

Change in sequence for gnatcatchers and gnatwrens

The new sequence is as follows:

Long-billed Gnatwren*

Tawny-faced Gnatwren*

Slate-throated Gnatcatcher*

Cuban Gnatcatcher*

Yucatan Gnatcatcher*

White-browed Gnatcatcher* (see below)

Blue-gray Gnatcatcher

Black-tailed Gnatcatcher

California Gnatcatcher

Black-capped Gnatcatcher

White-lored Gnatcatcher*

Change in sequence for waxbills

The new sequence is as follows:

Bronze Mannikin*

African Silverbill

Indian Silverbill*

Java Sparrow

Scaly-breasted Munia

Tricolored Munia

Red Avadavat*

Lavender Waxbill*

Orange-cheeked Waxbill*

Common Waxbill

Black-rumped Waxbill*

=== Further changes affecting only Middle America and the Caribbean ===

(Single asterisks are no longer used.)

Split of Barred Owl

Barred Owl (Strix varia)

Cinereous Owl (Strix sartorii)

Thanks to recent (2015) fieldwork by Nathan Pieplow and Andrew Spencer, what had long been considered the Mexican population of Barred Owl is now treated as a full species. Cinereous Owl is a mysterious species which is known from only a handful of contemporary sites.

Split of Brown-headed Nuthatch

Brown-headed Nuthatch (Sitta pusilla)

Bahama Nuthatch (Sitta insularis)

Notable here are Bahama Nuthatch’s extreme risk of extinction and that it was split without genetic data. Instead, the committee based its decision on vocalizations and playback experiments, which is unusual these days.

Split of Long-billed Gnatwren

Long-billed Gnatwren (Ramphocaenus melanurus)

Chattering Gnatwren (Ramphocaenus sticturus)**

Different vocalizations and no interbreeding in areas of sympatry (overlap) in South America.

Split of Tropical Gnatcatcher

Tropical Gnatcatcher (Polioptila plumbea)**

White-browed Gnatcatcher (Polioptila bilineata)

The “Tropical Gnatcatchers” of Middle America are now split as a different species; Tropical Gnatcatcher (sensu stricto) occurs in South America.

Split of Spotted Nightingale-Thrush

Yellow-throated Nightingale-Thrush (Catharus dryas)

Speckled Nightingale-Thrush (Catharus maculatus)**

These two species are separated by a large distance, as southern Central America lacks either. Yellow-throated is endemic to Mexico and northern Central America; Speckled is endemic to South America. On a personal note, I am grateful the committee avoided creating two new patronymic names, as Gould’s and Sclater’s were, respectively, the most obvious choices for new English names.

Split of Scrub Euphonia

West Mexican Euphonia (Euphonia godmani)

Scrub Euphonia (Euphonia affinis)

With this split, Mexico gains another endemic bird species. West Mexican Euphonia is found on the Pacific slope of Mexico from Sonora south to at least Guerrero. Scrub Euphonia is found from Tamaulipas on the Gulf slope and Oaxaca on the Pacific slope south to northwestern Costa Rica. Adult males of the two species differ in the color of the undertail coverts (white in West Mexican, Yellow in Scrub sensu stricto). Vocalizations differ slightly. West Mexican’s whistled jing call (often given in series) averages burrier and stronger; it also lacks a drop in pitch as is typical in Scrub. West Mexican’s song may average less complex, with fewer whistles and more unmusical twittering.

Split of Rufous-capped Warbler

Rufous-capped Warbler (Basileuterus rufifrons)

Chestnut-capped Warbler (Basileuterus delattrii)

Chestnut-capped Warbler replaces Rufous-capped Warbler in southeast Chiapas and most of Central America. It differs visually in having the malar mostly yellow. It also often has large white crescent under eye that contrasts with extensively rufous auriculars. (This area blends into the whitish malar on Rufous-capped.) Chestnut-capped’s underparts are entirely yellow, unlike the white-bellied Rufous-capped Warbler. Compared to Rufous-capped, Chestnut-capped’s relatively shorter tail is less often cocked as high. Its call is brighter and more piercing than Rufous-capped’s: a metallic tsinp!, suggesting Hooded Warbler, and its calls are routinely given in series. Its song is less harsh than Rufous-capped’s and is made up mostly of sweet chips and short, slurred whistles. Consistent differences in song—even where the two species meet in Guatemala and Chiapas—were, in addition to genetic data, a major factor in this split. Past reported hybridization now widely accepted to have been in error.

Split of Puerto Rican Bullfinch

Puerto Rican Bullfinch (Melopyrrha portoricensis)

St. Kitts Bullfinch (Melopyrrha grandis)*†

Sadly, you can’t go look for the newly minted St. Kitts Bullfinch. It was last seen alive in 1929 and is presumed extinct.

Split of Blue-winged Parrotlet

Turquoise-winged Parrotlet (Forpus spengeli)**?

Blue-winged Parrotlet (Forpus xanthopterygius)**

Blue-winged Parrotlet is endemic to South America. There is effectively no change for North America, where Turquoise-winged is considered of hypothetical occurrence.

Goodbye, Pseudoscops!

Striped Owl (Pseudoscops clamator Asio clamator)

Jamaican Owl (Pseudoscops grammicus Asio grammicus)

Pseudoscops has been absorbed into Asio as the status quo made Asio polyphyletic.

Goodbye, Deltarhynchus!

Flammulated Flycatcher (Deltarhynchus flammulatum Ramphotrigon flammulatum)

The genus Deltarhynchus has been absorbed into the (until now South American) genus Ramphotrigon. The three South American species are all known as flatbills, so it’s a little puzzling to me that the English name didn’t change to Flammulated Flatbill.

Split of Russet Antshrike

Russet Antshrike (Thamnistes anabatinus)

Rufescent Antshrike (Thamnistes rufescens)**

Rufescent Antshrike is endemic to South America. There is effectively no change for North America

Split of Yellowish Pipit

Yellowish Pipit (Anthus lutescens)

Peruvian Pipit (Anthus peruvianus)**

Peruvian is endemic to South America. There is effectively no change for North America.

Non-green Chlorophonias!

The yellow-rumped and blue-hooded species of euphonia have been move into the genus Chlorophonia. The males of these species lack green, but the females, like most female euphonias, are largely olive. Their songs and calls are, however, said to sound decidedly green by some.

Elegant Euphonia (Euphonia elegantissima Chlorophonia elegantissima)

Antillean Euphonia (Euphonia musica Chlorophonia musica)

Golden-rumped Euphonia (Euphonia cyanocephala Chlorophonia cyanocephala)**

Hello, Philodice!

Magenta-throated Woodstar (Calliphlox bryantae Philodice bryantae)

Purple-throated Woodstar (Calliphlox mitchellii Philodice mitchellii)

The two southern Central American woodstars are changing genera.

Change in sequence for euphonias

The new sequence is as follows:

Elegant Euphonia

Antillean Euphonia

Yellow-collared Chlorophonia

Blue-crowned Chlorophonia

Golden-browed Chlorophonia

Jamaican Euphonia

West Mexican Euphonia

Scrub Euphonia

Yellow-crowned Euphonia

White-vented Euphonia

Yellow-throated Euphonia

Thick-billed Euphonia

Spot-crowned Euphonia

Olive-backed Euphonia

Fulvous-vented Euphonia

Tawny-capped Euphonia

Orange-bellied Euphonia


Proposals not accepted included splits of Magnificent Frigatebird, Swainson’s Thrush, and Rufous-backed Robin; and lumping of McKay’s and Snow buntings.