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The to the American Ornithological Society's (AOS) , published 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, detailed below, include species splits for Myiarchus nuttingi, Vireo gilvus, and Larus argentatus; the addition of subfamilies in the Laridae for white-terns and noddies; and a merging of three families of Caribbean nine-primaried oscines.

The Check-list, published since 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.

New species, genera, and subfamilies

Until recently, it was thought that the Nutting's Flycatcher (Myiarchus nuttingi) complex consisted of three subspecies: M. n. inquietus in western Mexico, and M. n. nuttingi and M. n. flavidior in Middle America. An analysis of hundreds of sound recordings of these subspecies, among other data, resulted in a species split and elevation to species status for M. flavidior, now called Salvadoran Flycatcher.

In their proposal (), authors Roselvy Juárez, John van Dort, and Oscar Johnson stated, "The two taxa are sympatric in multiple locations with no sign of interbreeding, have diagnostic songs that are as different as those between other species of Myiarchus, and occupy different habitats across a broad swath of Central America."

"The vocal differences were quantified nicely," Chesser remarks, "And the fact that there's no evidence of interbreeding where these species co-occur clinched the argument for species status."

NACC co-chair Carla Cicero submitted a proposal () to elevate different subspecies of Vireo gilvus (Warbling Vireo) to species status.

As it turns out, the Eastern (gilvus) subgroup and the Western (swainsoni) subgroups "are separate species based on differences in a suite of characters, including genetics, vocalizations, and molt and migration; importantly, these differences are maintained where they breed parapatrically," says Chesser.

These species breed assortatively where they meet, despite low levels of hybridization. Vireo swainsoni is now the Western Warbling-Vireo, and V. gilvus is now the Eastern Warbling-Vireo.

Despite some striking morphological similarities, hawks within the genus Accipiter have been found through new molecular evidence not to comprise a monophyletic group, as documented in a proposal () by Shawn M. Billerman. He proposed a new generic arrangement of species within the family Accipitridae, including adding two new genera to the Check-list.

Notably, this revision resulted in the transfer of Accipiter cooperii (Cooper's Hawk) and several other hawks from Accipiter into the newly recognized genus Astur. This might be surprising to birders, considering the striking morphological similarities between A. cooperii, which is now in Astur, and A. striatus (Sharp-shinned Hawk), which will remain in Accipiter.

"People have trouble telling Cooper's and Sharp-shinned Hawks apart, but it turns out that they're not that closely related," Chesser remarks. "Raptors in general show a lot of convergence, and it turns out that the harriers are actually more closely related to species of Astur than Astur and Accipiter are to each other."

Other hawk species moved to Astur include A. gundlachi (Gundlach's Hawk), A. bicolor (Bicolored Hawk), A. gentilis (Eurasian Goshawk), and A. atricapillus (American Goshawk), and A. soloensis (Chinese Sparrowhawk) has been transferred to the genus Tachyspiza.

The large, complex family Laridae has undergone some significant changes at several taxonomic levels as a result of two proposals ( and ).

Within the long-confounding genus Larus, which includes the large white-headed gulls, L. argentatus (formerly Herring Gull) has been split into four species based on an array of genetic, phenotypic, ecological, and vocal differences: L. argentatus (now European Herring Gull), L. vegae (Vega Gull), and L. smithsonianus (American Herring Gull) as well as the extralimital L. mongolicus.

Chesser explains more about the challenges within this group, saying, "They are closely related, recently separated, and they also hybridize. That presents a confusing genetic signature, but they do not appear to be each other's closest relatives, certainly not as a group."

Also, within the Laridae, the subfamily Sterninae has been significantly revised because some species have been shown to be more divergent from other terns than previously thought, based on a proposal () by H. Douglas Pratt and Eric VanderWerf, with contributions from the late Storrs Olson. Notably, birds of the genera Gygis (white-terns) and Anous (noddies) have been moved from the Sterninae into their own new subfamilies, Gyginae and Anoinae, respectively.

"We thought the white terns and noddies were closely related to each other and to other terns," Chesser explains, "but they're actually all quite distinct."

In addition, based largely on morphology, vocalizations, and, in one case, archaeological evidence of historical sympatry, G. candida (Blue-billed White-Tern) and G. microrhyncha (Little White-Tern) have been separated as new species from G. alba (now called Atlantic White-Tern).

Merger for three families of Caribbean nine-primaried oscines

A proposal () from Kevin J. Burns led to the merging of two families of Caribbean nine-primaried oscines into a third family, the Phaenicophilidae, which is now named the Greater Antillean Tanagers and comprises two subfamilies and nine species.

Data from multiple molecular phylogenetic studies provided evidence that these species constitute a monophyletic group resulting from an endemic Caribbean radiation, facts highlighted by the new family classification.

Species originally in the family Phaenicophilidae are also now placed in the subfamily Phaenicophilinae (Hispaniolan Tanagers) and those originally in the families Nesospingidae and Spindalidae now constitute the subfamily Spindalinae (Puerto Rican Tanagers and Spindalises).