Since 1886, a committee of the American Ornithologists’ Union—now called American Ornithological Society, or AOS—has been responsible for keeping the official, standardized list of North American bird species. Every summer this committee, usually referred to as the AOS Checklist Committee, publishes a supplement to summarize their latest work. This may result in changing some names or changing how some birds are classified, with two or more species being combined (“lumped”) into one, or with one species being separated (“split”) into two or more. Avid birders watch for this annual report to see if it will change their own personal life lists.
The 2024 supplement, published online in July, revealed an exceptionally active year for changes to names and classifications. For birders in the United States and Canada, the most notable shifts this year are the lumping of Common Redpoll and Hoary Redpoll into one species, the split of Brown Booby into two species, and the split of Cory’s Shearwater into two species. There were also many changes in scientific names and some changes in English names.
At the end of this article, I’ll include a list of all the update that affect bird species found in the United States and Canada (including rare visitors). But first, here are the highlights that are likely to draw the most interest.
A lump of redpolls
Long discussed and debated, it finally happened: Common Redpoll and Hoary Redpoll were combined into one species. These tiny finches nest across Alaska and northern Canada, with flocks moving south irregularly in winter to southern Canada and the northern states. The palest birds from the northernmost part of the breeding range were long regarded as a separate species, Hoary Redpoll, and birders would try to identify them among winter flocks of Commons. Although fully typical individuals might be obvious, there were always borderline cases that defied easy ID. Those borderline cases were also problematic for scientists trying to draw firm lines between the species. The AOS Checklist Committee had considered lumping the redpolls before, as recently as 2017, and they still may admit to some lingering doubts, but this time new genetic evidence pushed them over the edge. So Common Redpoll, Hoary Redpoll, and the Lesser Redpoll of Europe are now all combined in a species simply called Redpoll (Acanthis flammea).
Birders can still enjoy looking for Hoary Redpolls among the winter flocks, and knowing that these frosty birds probably came from extremely far north, but we don’t have to worry about whether a particular individual is pale enough to count on our life lists.
Two seabirds splits
Avid birders on boat trips off our Atlantic Coast have paid close attention to Cory’s Shearwaters in recent years. Among the typical Cory’s, which come from islands in the eastern Atlantic, they were spotting a few of the “Scopoli’s” type from the Mediterranean, with more white under the wing and a thinner bill shape. Recent studies have shown that these are actually distinct, so they will be listed as two species: Cory’s Shearwater (Calonectris borealis) and Scopoli’s Shearwater (Calonectris diomedea).
The Brown Booby, a strong-flying tropical seabird, is common in the Caribbean and off the west coast of Mexico (and in Hawaii). In the continental U.S., historically it was seen mainly in Florida. But with a range expansion possibly linked to a warming climate, Brown Boobies are now seen often along our southern Atlantic and Gulf Coasts, and north along the California coast as well. And according to recent research, these populations represent two different species. The birds in the Caribbean and the southeastern U.S. (and in Hawaii) will still be called Brown Booby (Sula leucogaster), but those off California and western Mexico are now the Cocos Booby (Sula brewsteri), with the common name coming from the Cocos tectonic plate. In the Cocos Booby, the adult male has a whitish head and upper neck and the female has a white forehead, while in the Brown Booby, adults have entirely dark brown heads.
The bonus pipit
For years, avid birders along the Pacific Coast have scanned through migrating flocks of American Pipits, hoping to spot an example of the Siberian subspecies. Now that effort will add to their life lists, because that bird is being raised to the status of a full species. It will be called Siberian Pipit (Anthus japonicus) while the widespread form in North America will still be called American Pipit (Anthus rubescens).
New names for familiar birds
Here's a quick rundown of the notable changes for species in your field guide.
Barn Owl: Some North American birds are getting new names because of changes in classification elsewhere. The Barn Owl (Tyto alba) used to be considered a worldwide species, but now it has been split into three species, with the one here to be called American Barn Owl (Tyto furcata).
House Wren: The House Wren is being split into seven different species, but six of them are found only in the tropics, from Mexico to South America or on Caribbean Islands. Ours will be called the Northern House Wren and will keep the scientific name Troglodytes aedon.
Cattle Egret: The Cattle Egret is being split into two species, and moved to a different genus. So the bird in the Americas, as well as in Europe and Africa, is now Western Cattle-Egret (Ardea ibis). The other bird in the complex, the Eastern Cattle-Egret, lives in the region from eastern Asia to Australia and New Zealand, and it has strayed to Alaska at least once.
Audubon’s Shearwater: The bird formerly known as Audubon’s Shearwater is being split into five species, distributed in various tropical and subtropical seas around the world. To avoid confusion, all are being given new English names. The one found off our southern Atlantic Coast will now be called Sargasso Shearwater (Puffinus lherminieri), named for the Sargasso Sea.
Lesser Sand-Plover: Thanks to a species split and a move to a different genus, the Lesser Sand-Plover (rare in Alaska and elsewhere) is becoming the Siberian Sand-Plover (Anarhynchus mongolus).
Hyphen Havoc: Three other English bird names are merely losing a hyphen. Black-crowned Night-Heron becomes Black-crowned Night Heron and Yellow-crowned Night-Heron becomes Yellow-crowned Night Heron. The Japanese Bush-Warbler (introduced in Hawaii) becomes Japanese Bush Warbler. Disagreements about the use of hyphens in bird names have been going on for at least half a century, and they’re likely to continue.
Summary of 2024 changes to the United States/Canada bird list
The list below summarizes all the above revisions and adds a few other cases in which only the scientific names are being altered. All in all, quite a year for changes!
1. Gray Francolin (Hawaii): from Francolinus pondicerianus to Ortygornis pondicerianus.
2. Double-striped Thick-knee (rare visitor): from Burhinus bistriatus to Hesperoburhinus bistriatus.
3. Eurasian Dotterel (rare): from Charadrius morinellus to Eudromias morinellus.
4. Lesser Sand-Plover (Charadrius mongolus) becomes Siberian Sand-Plover (Anarhynchus mongolus).
5. Greater Sand-Plover (rare): from Charadrius leschenaultii to Anarhynchus leschenaultii.
6. Wilson’s Plover: from Charadrius wilsonia to Anarhynchus wilsonia.
7. Collared Plover (rare): from Charadius collaris to Anarhynchus collaris.
8. Mountain Plover: from Charadrius montanus to Anarhynchus montanus.
9. Snowy Plover: from Charadrius nivosus to Anarhynchus nivosus.
10. Cory’s Shearwater is split into two species: Cory’s Shearwater (Calonectris borealis) and Scopoli’s Shearwater (Calonectris diomedea).
11. Audubon’s Shearwater (Puffinus lherminieri) becomes Sargasso Shearwater.
12. Brown Booby is split into two species: Brown Booby (Sula leucogaster) and Cocos Booby (Sula brewsteri).
13. Yellow Bittern (rare): from Ixobrychus sinensis to Botaurus sinensis.
14. Least Bittern: from Ixobrychus exilis to Botaurus exilis.
15. Intermediate Egret (rare) becomes Medium Egret.
16. Cattle Egret (Bubulcus ibis) becomes Western Cattle-Egret (Ardea ibis).
17. Black-crowned Night-Heron becomes Black-crowned Night Heron.
18. Yellow-crowned Night-Heron becomes Yellow-crowned Night Heron.
19. Barn Owl (Tyto alba) becomes American Barn Owl (Tyto furcata).
20. Brown Jay: from Psilorhinus morio to Cyanocorax morio.
21. Japanese Bush-Warbler (Hawaii) becomes Japanese Bush Warbler.
22. House Wren (Troglodytes aedon) becomes Northern House Wren.
23. American Pipit is split into two species: American Pipit (Anthus rubescens) and Siberian Pipit (Anthus japonicus).
24. Common Redpoll and Hoary Redpoll are combined into one species, Redpoll (Acanthis flammea).
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