64th Supplement to the Check-list of North American Birds published

[Laura Bies]

The 64th Supplement to the American Ornithological Society’s (AOS) Check-list of North American Birds, published today in Ornithology, includes numerous updates to the classification of North American bird species. 

A few highlights from this year’s supplement, detailed below, include a species lump for the Western Flycatcher, species status for the goshawk of North America, and species splits in several Caribbean birds leading to five additional species. 

The Check-list, published since 1886, is updated annually by the AOS’s North American Classification Committee (NACC), the official authority on the names and classification of the region’s birds, and is consulted by birders and professional ornithologists alike. 

The full Check-list supplement is available at: https://doi.org/10.1093/ornithology/ukad023.

Species Lumps and Splits

(Re)lumping of Cordilleran Flycatcher and Pacific-slope Flycatcher as Western Flycatcher 

In 1989, the Western Flycatcher (Empidonax difficilis) was split into the Pacific-slope Flycatcher (E. difficilis) and the Cordilleran Flycatcher (E. occidentalis), based mainly on research that identified differences in vocalizations and allozyme frequencies, differences maintained across a small contact zone in California. “These flycatchers are suboscine birds, so vocalizations are extremely important in determining species limits,” NACC chair R. Terry Chesser of the U.S. Geological Survey explains. Researchers W. Alexander Hopping, Ethan Linck, and others recently studied a separate contact zone in a large region of the northern Rockies, which was not known when the previous research led to the species split. This region includes parts of the U.S. states of Washington, Idaho, and Montana, as well as the Canadian provinces of British Columbia and Alberta. Hopping and Linck (in Proposal 2023-D-7) noted that the morphology, vocalizations, and genetics of the Cordilleran Flycatcher and Pacific-slope Flycatcher are not consistently distinguishable in this broad region. “According to the proposal, bird record committees in this area list only a single default species rather than expecting people to identify individual birds as Cordilleran or Pacific-slope,” Chesser says. Thus, although the lump will result in the loss of a species for North America, bird identification should be more straightforward for regional checklists.

Species Split for Northern Goshawk 

The Northern Goshawk (Accipiter gentilis) is being split into two species. A proposal (Proposal 2023-B-11) from NACC member Shawn M. Billerman of the Cornell Lab of Ornithology highlights key vocal and genetic differences between what had been treated as two subspecies groups within Northern Goshawk, the Palearctic gentilis and Nearctic atricapillus groups. Because the newly recognized Eurasian Goshawk (A. gentilis) has occasionally been recorded from North America, a few lucky bird enthusiasts might be able to include both Eurasian Goshawk and American Goshawk (A.atricapillus) on their North American lists. “This is an interesting split not only because both species are known from North America, one as a resident and the other as an accidental, but because two different subspecies of the Eurasian Goshawk are known from North America,” Chesser says. “Two individuals of the Asian subspecies albidus have turned up in Alaska, and there’s an old specimen of the European subspecies gentilis from Labrador.”

Five Newly Split Species in the Caribbean

The AOS’s NACC and SACC (South American Classification Committee) members are collaborating with the Working Group on Avian Checklists, which is part of the International Ornithologists’ Union, to consolidate the four main global checklists into a single standardized checklist. “The four global checklists differ in many ways, such as whether to recognize particular species splits or what genus a species belongs to,” Chesser explains, adding, “The working group, which includes two members from NACC and one from SACC, is going through all the discrepancies among the four main lists and trying to resolve them.” As part of this effort, Chesser and other NACC members have been preparing proposals to help reconcile the differences that involve North American birds. This year, their efforts resulted in the recognition of five additional bird species in the Caribbean, among others.

Cuban Bullfinch Species Split

The Cuban Bullfinch (Melopyrrha nigra), a finch-like tanager, is being split into two species, Cuban Bullfinch (M. nigra), now restricted to Cuba, and Grand Cayman Bullfinch (M. taylori). The NACC passed a proposal by NACC members Jonathan Dunn and Chesser (Proposal 2023-A-13) to split the bullfinch after re-evaluating evidence showing song and morphological differences. Significantly, the research supporting the split was spurred on by a birdwatcher’s observations of song differences between individuals on Cuba and Grand Cayman. “It goes to show that amateur ornithologists can, and do, make very real contributions to the field of ornithology; in this case their comments led to further important research,” Dunn and Chesser wrote in their proposal.

Greater Antillean Nightjar Species Split

The Greater Antillean Nightjar (Antrostomus cubanensis) is being split into two species based on vocal differences. Former subspecies ekmani, whose range includes the western third of the Dominican Republic and the western part of the Tiburon Peninsula, Haiti, is being elevated to species status. A proposal (Proposal 2023-A-2) submitted by NACC members Dunn, Chesser, and Carla Cicero summarized the convincing differences between what will now be the Cuban Nightjar (A. cubanensis) and the Hispaniolan Nightjar (A. ekmani). 

Three-way Split for Antillean Euphonia

The Antillean Euphonia (Chlorophonia musica) is a small, attractive woodland finch found on many Caribbean islands. This species formerly consisted of three subspecies that will now be considered separate species. Researchers Nicholas A. Mason, Samantha L. Rutledge, and David Vander Pluym from Louisiana State University recommended the split in a new proposal (Proposal 2023-B-7) based largely on plumage differences on a par with those between other species of euphonia; the three species will now be the Hispaniolan Euphonia (C. flavifrons), Puerto Rican Euphonia (C. sclateri), and Lesser Antillean Euphonia (C. musica).

Palm Crow Species Split

The Palm Crow (Corvus palmarum), a corvid long shared between Hispaniola and Cuba, will now be treated as two species: the Hispaniolan Palm Crow (C. palmarum) and the Cuban Palm Crow (C. minutus), thus adding another species to the Check-list area. NACC member Pamela C. Rasmussen, then at Michigan State University (now at Cornell Lab of Ornithology), based her proposal (Proposal 2023-B-8) primarily on differences in vocalizations, genetic evidence, and apparent differences in tail-flicking behavior. Based on the vocalizations alone, “We're surprised that they hadn't been split before,” Chesser says. “If we can tell the calls apart, probably the birds can also tell them apart.”

Transfers Between Genera

New Genus for Tiny Hawk

The Tiny Hawk (now Microspizias superciliosus) was for many years placed in Accipiterand has been treated as such by both the North and South American checklists. NACC Early Career Systematics Group member Max T. Kirsch of San Diego State University and Rasmussen submitted a proposal (Proposal 2023-B-10) to transfer the Tiny Hawk to the new genus Microspizias, based on research that identified substantial morphological and molecular differences between the Tiny Hawk and other species of Accipiter.

Other species transferred between genera include three species of Neotropical crake, as well as the critically endangered Zapata Rail (now Mustelirallus cerverai), the Thicket Antpitta (now Myrmothera dives), and the Crimson-collared Grosbeak (now Periporphyrus celaeno).