The 67th Supplement to the American Ornithological Society's (AOS's) Check-list of North American Birds, which was 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.
This year, the committee revisited the case of Tringa semipalmata (Willet), an issue previously considered in 2017 (2017-A-10), based on a new 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 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). 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, based on 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.
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 Rasmussen's proposal (2026-B-9).
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 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.
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.
Sixty-seventh Supplement to the American Ornithological Society's Check-list of North American Birds, Ornithology (2026). DOI: 10.1093/ornithology/ukag037
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Originally reported by Phys.org.