We Now Have Two Warbling Vireos
Written by Andy McCormick
Andy McCormick, 2024 Audubon Washington Helen Engle Volunteer of the Year
The annual review of the American Ornithological Society (AOS) checklist for the taxonomic order of birds has been completed, and splitting of bird species into two or more independent species was a highlight of changes again this year. The most notable split among birds of the United States and Canada is that of the Warbling Vireo. For those traveling in Mexico splits of Squirrel Cuckoo and Nutting’s Flycatcher are significant, and anyone heading to Great Britain will likely welcome the split of Red Grouse. Hawaiian birders will now list the Blue-billed White Tern because White Tern has been split.
EASTERN AND WESTERN WARBLING VIREO
Differences in plumage, structure, and songs of these two vireos have been known for many years and this summer the Committee on Classification and Nomenclature of North and Middle American Birds (NACC) finally separated them. The song of the Western Warbling-Vireo (Vireo swainsoni) is a fairly short, alternatingly rising and falling, burry song. The bill of the Western is smaller than that of the Eastern and the plumage tends to be duller. The Eastern Warbling-Vireo (Vireo gilvus) in contrast, has a longer more melodious song, longer bill, and is more yellow on the flanks.
Fortunately for birders hoping to identify them, the two species overlap geographically only in a small area of contact in the Great Plains and in the province of Alberta. The two species are also separated in winter. The Western winters in Mexico north of the Isthmus of Tehuantepec, and the Eastern is found south of the Isthmus as far as Costa Rica.
MEXICAN SQUIRREL-CUCKOO
In Mexican bird news, Squirrel-Cuckoo has been split into Mexican Squirrel Cuckoo (Piaya mexicana), which is found on the Pacific Slope of Mexico. It is larger with more pale rufous color extending to the underside of the tail. The more southerly Common Squirrel-Cuckoo (Piaya cayana) is darker rufous with black and white under the tail. The two species come in contact in eastern Oaxaca but there seems to be no interbreeding.
NUTTING’S AND SALVADORAN FLYCATCHERS
Another change affecting Mexico’s birds also results in the splitting of a Pacific Coast species. The Salvadoran Flycatcher (Myiarchus flavidior) was considered a subspecies of Nutting’s Flycatcher (Myiarchus nuttingi), but it has been split and is now has full species status. Different vocalizations are what gave rise to this split. Salvadoran Flycatcher is found along the Pacific Slope of Mexico south from Chiapas to Nicaragua and Honduras.
WILLOW PTARMIGAN AND RED GROUSE
Travelers to the British Isles will now identify the red form of the Willow Ptarmigan (Lagopus lagopus) as its own species called Red Grouse (Lagopus scotica). The Red Grouse is a heath-dwelling endemic species which does not molt into a white winter plumage as Willow Ptarmigan does everywhere else.
WHITE TERN IS SPLIT INTO THREE SPECIES
The Blue-billed White Tern (Gygis candida) is now the name of the lovely tern that nests at Waikiki on Oahu in Hawaii. The Little White Tern (Gygis microrhyncha) is a bird of the Marquesas Islands in French Polynesia in the South Pacific, and the Atlantic White Tern (Gygis alba, sensu stricto) is a bird of the South Atlantic.
Thanks to the work of Michael Retter editor of special editions on Birding magazine published by the American Birding Association for sorting through the full report to highlight the changes most likely to affect birders in the ABA area.
Photo Credit: Mick Thompson