In with the Old, Out with the Mew

Update to the Check-list of North American Birds Publishes Today in Ornithology

Keep your checklists handy because the 62nd Supplement to the American Ornithological Society’s Check-list of North American Birds, publishing today in Ornithology, includes numerous updates to the classification of the continent’s bird species. A few highlights from this year’s supplement, detailed below, include species splits for Mew Gull, Barred Owl, and Sedge Wren, among quite a few others; a transfer back to an old genus for Ruby-crowned Kinglet; and a revision of the linear sequence of passerine families. 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:

Species Splits

Splitting of Barred Owl and Cinereous Owl (Proposal 2021-C-8)

Based primarily on differences in vocalizations, the Barred Owl (Strix varia) is being split into two species, the Barred Owl, which retains its English and scientific names for U.S. and Canadian populations, and the Cinereous Owl (Strix sartorii) for its counterpart in Mexico. “Vocalizations are particularly important for species recognition in owls,” NACC chair Terry Chesser of the U.S. Geological Survey explains. The proposal to split Barred Owl into two species, submitted by Nathan Pieplow (University of Colorado Boulder) and Andrew Spencer (Cornell Laboratory of Ornithology), focused on key differences in both their rhythm and series songs, specifically in the series song, which they summarize as: “[sartorii’s] syncopated beginning, its uniformity in pitch, and its lack of a drawn-out ‘hoo-wah’ note at the end. In the Barred Owl’s series song, the highest and loudest notes are at the end, while in that of sartorii, the highest and loudest notes are in the middle.” 

Pieplow and colleagues were surprised and dismayed, when returning to many previously known locations to record vocalizations of Cinereous Owl, that there appears to have been a severe decline and reduction in range for this species. Moreover, while searching at sites in Oaxaca, Mexico, where this species had previously been found, they instead observed the Fulvous Owl (Strix fulvescens), a close relative more typically found farther south in Mexico and Central America, but which appears to have extended its range northward.

Splitting of Mew Gull into Common Gull and Short-billed Gull (Proposal 2021-A-3)

“If you’re a coast-to-coast birder, you may be able to pick up a new species this winter,” Chesser quips, describing the split of Mew Gull (Larus canus) into two species: Common Gull (Larus canus) and Short-billed Gull (Larus brachyrhynchus), the name used for this species as long ago as the first edition of the Check-list in 1886. The Common Gull breeds in Eurasia and is a casual visitor to the eastern U.S. and Canada, and occasionally ventures to Alaska, whereas the Short-billed Gull breeds in northwestern North America and winters south along the Pacific coast and also into the interior, primarily of the western U.S. This split is based mainly on differences in display vocalizations but also on genetic and other morphological differences outlined in a proposal by NACC member Pamela C. Rasmussen (Michigan State University). These species had been lumped based on what is now viewed as weak evidence from a paper published in 1919. 

Splitting of Sedge Wren and Grass Wren (Proposal 2021-C-3)

Previous ideas about how Sedge Wren (Cistothorus platensis) should be divided turn out to be misguided, according to Chesser, who authored a proposal, based in part on a prior proposal to South American Classification Committee (SACC), to split this species. In the 1998 Check-list, Sedge Wren was considered a single species distributed from Canada to extreme southern South America, comprising three distinct groups: stellaris, whose range extended from Canada to Panama, and two other groups distributed in South America, platensis and polyglottus. However, the species split, which is based on vocalizations and genetics, does not occur where we might have expected it would, based on what we thought we knew about intraspecific variation in the species. Instead, it turns out that the populations breeding in Canada and the U.S. are distinct from all other populations, including those breeding in Mexico, Central America, and South America, and are being split from the rest. The new southern species, Grass Wren (Cistothorus platensis), will retain the scientific name due to reasons of priority, but the new northern species will keep the English name Sedge Wren (Cistothorus stellaris). The SACC had previously made this split after consideration of the separate proposal to that committee.

Transfers Between Genera

A New (Old) Genus for the Ruby-crowned Kinglet (Proposal 2021-A-9)

The Ruby-crowned Kinglet (Regulus calendula, now Corthylio calendula), a tiny olive-colored songbird with a bright red but hard-to-see crown in males, breeds in forests across the U.S. and Canada and winters as far south as Central America. It’s one of six species in the family Regulidae, all currently placed in the same genus, Regulus. Two species are found in the New World, Golden-crowned Kinglet (Regulus satrapa) and Ruby-crowned Kinglet; and four species in the Old World, including the Firecrest (Regulus ignicapilla) and Goldcrest (Regulus regulus). In the 1931 AOU Check-list, the Ruby-crowned Kinglet had been transferred to its own genus, Corthylio, based on morphological differences from the other species, but as of the 1957 Check-list it was returned to Regulus, with Corthylio relegated to subgenus status, and it has been placed in Regulus ever since. 

“It has long been known that the Ruby-crowned Kinglet is markedly divergent from the other regulids in plumage and other aspects of external anatomy, reflected by the fact that the genus Corthylio Cabanis, 1853, was erected for this species,” authors Brandon Woo and Natalia C. García (Cornell University) and NACC member Pamela C. Rasmussen (Michigan State University) state in their proposal. Moreover, vocal and genetic data, including molecular studies dating from the early days of molecular systematics to the current genomics era, have consistently shown that the Ruby-crowned Kinglet is strikingly different from other species placed in Regulus

“This is my favorite proposal of the year,” Chesser notes, “and I think it will be interesting to birders for the same reasons. I hope this generates new appreciation for an unassuming little bird that is of great interest evolutionarily and really distinctive from other species in its family.”

Linear Sequence Revision

Revision of Linear Sequence of Passerine Families (Proposal 2021-B-7)

A proposal by Chesser and NACC member Shawn Billerman based on new, concordant information from three recent genomic studies of passerines has led to a reshuffling and update to the linear sequence of passerine families to better reflect their phylogenetic relationships. “This is a big step forward that reflects a wealth of new information on evolutionary relationships among passerine families,” Chesser explains. “This revision will create short-term disturbance, but we think this will be more than offset by the benefits of having a more scientifically accurate classification, which should be stable into the future, with occasional minor changes. The fact that several genomic studies produced virtually the same phylogeny was the key factor in convincing us that the time was right for this revision.”

About the Journal

Ornithology (formerly, The Auk: Ornithological Advances) is a peer-reviewed, international journal of ornithology published by the American Ornithological Society. The journal’s name changed to Ornithology in January of 2021. Ornithology commenced publication in 1884 and in 2009 was honored as one of the 100 most influential journals of biology and medicine over the past 100 years.

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