Lumped or Split?

 The 58th American Ornithological Society (AOU) Supplement Explained

A simple take on the latest AOU supplement, and what it means to us

The latest AOU supplement is now online! I'll admit, writing this is a little outside my comfort zone. I'm not the type of birder who memorizes the taxonomical order of the New World passerines, or eagerly awaits the annual taxonomical update. Like many birders, I didn't know the AOU changed to American Ornithological Society (AOS) until recently.  I'm learning more about birds step by step, and the recent update to AOU taxonomy piqued my curiosity- but "figuring out" all of the proposed lumps, splits, and re-arrangements isn't of too much interest to me. I recently read Rick Wright's take on the changes  which helped me understand the supplement better. This inspired me to write my own blurb from what I learned along with a few photos and links to make it fun. 

Summary of Changes (select changes relevant to U.S. birders)

A "Kumlein's" Gull, Race Point, Massachusetts, December 2016

A "Kumlein's" Gull, Race Point, Massachusetts, December 2016

Thayer's Gull: Gone

Initially thought to be a subspecies of Herring gull, then split and made its own species in 1973, the journey for Thayer's gull has been a long and confusing one. The decision to make Thayer's a standalone species may not have been entirely supported by evidence, so inevitably the Thayer's gull is lumped back in with Iceland. While it will make Iceland Gulls much easier for beginners to identify, I'm sure larophiles (gull-lovers) all over will continue to refer to it as a Thayer's gull (at least for a while) and hopefully someone will study these pale-winged / dark-winged gulls on their breeding range and figure out exactly what is going on. Anyone out there up for a challenge?

Declined Splits:

-Willet (Proposed to split into Eastern and Western Willet) Maybe someday this will happen...

-Yellow-rumped Warbler  (Proposed to be split along subspecies breaks- see below) 

Here's a figure from the proposal to split Yellow-rumped Warblers- cool stuff! 

Here's a figure from the proposal to split Yellow-rumped Warblers- cool stuff! 


Potential Splits?  Decide Another Day

Brown Creeper, Nashville Warbler, Bell's Vireo are all candidates to be split along Eastern/Western subspecies lines. This time around they were declined by the vote. 

Some of the committee's votes and reasons for birds in batch 'C' can be found here

Baird's Junco

Yellow-eyed Junco, Arizona 2016

Yellow-eyed Junco, Arizona 2016

Although it does not live in the ABA area, the Baird's junco is superficially similar to the Yellow-eyed Junco of southeastern Arizona. It is endemic to Baja Mexico, living in semi-arid woodlands. It has an extremely small range, and a population estimated to be less than 10,000 individuals. Recent data has justified making this little guy a separate species, and the vote passed this time around.

Magnificent No More! 

This Magnificent (Rivoli's) Hummingbird was seen in the mountains of Arizona on Christian's 2016 Big Year

This Magnificent (Rivoli's) Hummingbird was seen in the mountains of Arizona on Christian's 2016 Big Year

The Magnificent Hummingbird was named in honor of the Duke of Rivoli, after it was described in the 1920's. (The Anna's hummingbird is named after his wife, the Duchess of Rivoli)  It remained "Rivoli's Hummingbird" until the mid-1980's when it was re-named Magnificent. This recent Supplement has split Magnificent hummingbird back into the Rivoli's and Talamanca hummingbird (the latter is found in Costa Rica)

Did We Gain A Crossbill? 

Yes! The Cassia crossbill is found in Cassia county Idaho, differing from the Red Crossbill by call type and is isolated breeding range in the South Hills/Albion Mountains.  In previous literature, it has been referred to as the "South Hills Crossbill" (Benkman, 1999) however the supplement's language likely will help the 'Cassia' part of the name stick. 

Zak Pohlen's stunning photo of the Cassia crossbill from Idaho. Check out his eBird list to hear the great recordings he made documenting this species!

Zak Pohlen's stunning photo of the Cassia crossbill from Idaho. Check out his eBird list to hear the great recordings he made documenting this species!

Why didn't the Redpolls get lumped?

Many birders have talked about and anticipated the redpoll lump for some time now. We have three Redpoll species in North America: the Common, Hoary, and Lesser. (the latter accidental to ABA area) It seems like my entire adult birding life people have debated the Common and Hoary redpoll, and speculated about when they would be lumped. Well, friends- the redpoll complex lives another day. To read about the Redpoll systematics, click here.

One Harrier becomes Two

The Northern Harrier (Circus hudsonius) is split from the Eurasian Harrier, in a long-overdue decision on this side of the pond. The BOU (British Ornithological Union) announced their decision to split this species in Winter 2016, and it's appropriate the AOU would follow suit. DNA research shows our American Harrier is more closely linked to the Cinereous harrier of South America, than the Hen Harrier of Eurasia.


Most of these changes are beyond my comprehension, but I think that some folks are excited with the re-arranging (and for field guide authors, the opportunity to publish a new-edition of their field guides) The Yellow-breasted Chat now has its own family, Icteriidae, which if I understand it correctly, is different than the blackbirds and oriole family Icteridae (Does that confuse anyone else?) 

I'm sure there will be more to figure out when the entire supplement is released, but if you're interested in the disappearance of the Provost Ground-sparrow, I'd encourage you to check out some of the other great pieces written about those changes- or for a fun challenge in understanding taxonomy- tackle the supplement yourself!

More Information

UPDATE: This post from the ABA Blog goes into more detail of all the changes made in the ltest supplement- definitely worth the read!

Want to see the proposed changes: Visit the 2017 AOU Checklist Proposals:  Part A  -  Part B

Here's all of the accepted changes on the 58th Supplement



Christian Hagenlocher started The Birding Project in 2016 while doing an ABA Big Year. He finished the year with 752 species, over 730 of them documented with images and sound recording. He is working on completing a book, while traveling the country giving talks and mentoring young birders. If you'd like to contact Christian, please use the email below.

Mistakes, misspellings, and erroneous information is never intended! I am always learning and willing to take comments and feedback to improve the accuracy of this post. Teachers too are always learning! Email if any mistakes are found.