CHICAGO — October 20, 2026 — The 67th Supplement to the American Ornithological Society’s (AOS’s) Check-list of North American Birds, which published today in Ornithology, includes several significant updates to the classification of bird species found in North America, Central America, and the Caribbean.
A few highlights from the supplement include splits for Tringa semipalmata (Willet), Cistothorus palustris (Marsh Wren), Setophaga petechia (Yellow Warbler), and Turdus plumbeus (Red-legged Thrush). Also of note, Momotus mexicanus (Russet-crowned Motmot) has been split into two species, giving Guatemala its first endemic bird species, M. castaneiceps (Guatemalan Motmot); and Bubo virginianus (Great Horned Owl) has been split into four species, three of which are endemic to South America. American populations of two species, Ardea alba (Great Egret) and Numenius phaeopus (Whimbrel), have been split from their Old World counterparts, resulting in two new American endemics, A. egretta (American Egret) and N. hudsonicus (Hudsonian Whimbrel). We’ve gone through another “wrenaissance” this year, as one genus was added, one deleted, and the linear sequence was reordered for Troglodytidae.
The Check-list, first published in 1886, is updated in annual supplements from the AOS’s North American Classification Committee (NACC). The Check-list and its supplements provide the taxonomic and nomenclatural foundation for bird research, conservation, management, and education throughout the region, and are relied on as the authority on avian biodiversity by government agencies, NGOs, scientists, and birders, among others. The NACC reviews proposals submitted annually for taxonomic and distributional updates to the Check-list of North American Birds.
The full 2026 Check-list Supplement is available at: https://doi.org/10.1093/ornithology/ukag037
Splits within the Americas
This year, the committee revisited the case of Tringa semipalmata (Willet), an issue previously considered in 2017 (2017-A-10), based on a new and convincing proposal (2026-A-3), submitted by Pamela C. Rasmussen, Nicholas A. Mason, Michael O’Brien, Marshall Iliff, and Brian Sullivan. The new proposal suggested species status for eastern (T. semipalmata) and western (T. inornata) birds based on differences in vocalizations (including differential response to playback in semipalmata), ecology, morphology, annual cycle, and genetics. The new English names Prairie Willet (for T. inornata) and Saltmarsh Willet (for T. semipalmata) reflect the differences in breeding habitat of the two species.
The committee also passed a proposal (2026-B-2) from Jacob C. Cooper, a member of the committee’s Early Career Systematics Group, and Peggy M. Huss to split Cistothorus palustris (Marsh Wren) into two species, predicated on clear differences in vocalizations between eastern (C. palustris; now Eastern Marsh-Wren) and western (C. paludicola; now Western Marsh-Wren) populations. Of particular importance was research showing that although the two species occur in the same marshes across much of southern Saskatchewan, they rarely hybridize and their songs remain diagnostically different. “It is likely that these birds have only been considered conspecific until now because they are visually similar to the human eye,“ the authors say, adding, “although paludicola and palustris do hybridize, they are clearly undergoing strong selection for assortative mating in areas of overlap.” Committee Chair Terry Chesser further explains, “In the contact zone, birds singing the Eastern Marsh-Wren song nest right next to birds that sing the Western Marsh-Wren song. Occasional individuals sing both songs, but these are rare, and the genetics tell the same story, that there’s apparently strong selection against hybrids.”
Another notable split is that of the tropical sedentary species Setophaga petechia (Mangrove Warbler) from S. aestiva (Yellow Warbler), the migratory and more northern species. Evidence submitted by Shawn Billerman and Oscar Johnson (2026-B-13) suggested species-level differences in genetics, vocalizations, morphology, and natural history. “Some of the morphological differences are associated with the fact that S. petechia inhabits mangroves,” Chesser explains. For example, the proposal’s authors noted that “birds in mangrove habitats had larger bills and longer tarsi than those in inland habitats in North America, and that bill size for temperate inland populations increased with increasing temperature during the breeding season.”
We’re seeing the continuation of two recent trends with Caribbean birds: species splits and new records for Caribbean species in Florida. This includes a species split and new records for Turdus plumbeus (Red-legged Thrush), which typically occurs in the Greater Antilles, the Bahamas, and Dominica in the Lesser Antilles. The committee passed a proposal (2026-A-2) by Shawn M. Billerman, Nils Navarro Pacheco, and Javier Torres to split T. ardosiaceus (Eastern Red-legged Thrush) of Hispaniola, Puerto Rico, and Dominica, from T. plumbeus (Western Red-legged Thrush) of Cuba, the Bahamas, the Cayman Islands, and Swan Island, based on substantial differences in coloration and song pattern, as well as genetic differences. Of interest are recent records in Florida of T. ardosiaceus, including several from the Atlantic coast of the Bahamas subspecies and one from Key West of the Cuban subspecies.
Additionally, Margarops fuscatus (Pearly-eyed Thrasher) has been added to the list of species known from the U.S. based on a record from Key West, Florida, in the spring of 2024 (2026-C-2). An intrepid adventurer, M. fuscatus has occurred as a vagrant on several Caribbean islands outside of its typical and expanding range.
Three South American populations of Bubo virginianus (Great Horned Owl) have been split from B. virginianus and elevated to individual species status, thanks to a proposal by Dan Lane (2026-B-3), a member of the South American Checklist Committee (SACC). Lane described key differences in voice, morphology, and phylogenetic placement that warranted the change. B. nigrescens (Paramo Horned Owl) found in the Northern Andes; B. nacurutu (Tropical Horned Owl), found in tropical South America; and B. magellanicus (Magellanic Horned Owl), whose range extends from the southern cone of South America to as far north as the Central Andes, are three newly recognized species of owl you can add to your global checklist!
Momotus mexicanus (Russet-crowned Motmot), a colorful bird native to the tropical lowlands, dry forests, and scrublands of Mexico and Guatemala, has been split into two species, resulting in Guatemala’s first endemic bird species, M. castaneiceps (Guatemalan Motmot), found only in the dry Río Motagua valley. The split was based on striking differences in plumage of the crown, nape, and forehead; vocalizations; and genetics described in Roselvy Juárez and Pam Rasmussen’s proposal (2026-B-9).
Old World-New World splits
The globally distributed species Ardea alba (Great Egret) has been split along geographical lines. The name A. alba stays with the Old World species (Great White Egret), whereas the species in the Americas becomes A. egretta (American Egret), adopting an English name used prior to Great Egret. In a proposal by Pamela C. Rasmussen, Jon Dunn, and Andrew Spencer (2026-A-8), the authors based their recommendations primarily on differences in vocalizations, breeding soft-part coloration, and plume structure.
An undergraduate student at Stanford University, Martin Freeland, proposed (2026-A-9) a split of Numenius phaeopus (Whimbrel) based on differences in courtship and agonistic displays, morphology, and genetics. This split, newly adopted by the committee, was previously considered but failed in 2022 (2022-A-10). The populations that breed in Canada and Alaska are now separated as N. hudsonicus (Hudsonian Whimbrel), whereas the Old World species becomes N. phaeopus (Eurasian Whimbrel). Based in part on his proposal, Freeland was invited to join NACC’s Early Career Systematics Group, which is open to students and postdocs and fosters a new generation of scientists willing and able to contribute to the work of the committee.
Reorganizations
This year, in an effort to more accurately reflect their evolutionary relationships, the NACC changed species sequences for the Troglodytidae (wrens), and to a lesser extent the Sittidae (nuthatches) and Polioptilidae (gnatcatchers). In yet another “wrenaissance,” this year one genus (Nannus) was added (for Winter and Pacific wrens), one subtracted (Thryorchilus, which is now merged with Troglodytes), and the linear sequence rearranged.
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The journal Ornithology is a peer-reviewed, international journal of ornithology published by the American Ornithological Society (AOS). Ornithology (formerly The Auk) commenced publication in 1884 under the banner of the American Ornithologists’ Union, the AOS’s predecessor society. In 2009, Ornithology was honored as one of the 100 most influential journals of biology and medicine over the past 100 years.
About the American Ornithological Society
The American Ornithological Society (AOS) is an international society dedicated to connecting ornithologists, science, and bird conservation by supporting science that advances the understanding and conservation of birds; promoting broad access to ornithological science; supporting ornithologists throughout their career paths; and fostering a welcoming, diverse, supportive, and dynamic ornithological community. The AOS publishes two top-ranked international scientific journals, Ornithology and Ornithological Applications, and hosts an annual conference that attracts ornithologists from across the globe. Its robust grants program supports student and early-career professional research initiatives. The society’s check-lists serve as the accepted authorities for scientific nomenclature and English common names of birds in the Americas. The AOS is also a partner with The Cornell Lab of Ornithology in the online Birds of the World, a rich database of species accounts of the world’s birds. The AOS is a 501(c)(3) nonprofit organization serving about 3,000 members globally. For more information, see www.americanornithology.org.