In birding, a split is when scientists divide one species into two or more, and a lump is when they merge two or more species into one. Either can change your life list without a new sighting: a split can add a species you'd already seen, and a lump can take one away.
That's why your total can move while you sit at home. Here's what each one means, the recent changes North American birders noticed, and what happens to your records.
Key facts
- Herring Gull became four species in August 2025 (AOS). For most US birders, theirs is now American Herring Gull.
- Redpolls: in July 2024 the AOS merged Hoary and Lesser Redpoll with Common Redpoll, now one species.
- eBird updates its taxonomy once a year, in October, and applies the changes to your old records for you.
- AviList, the shared global checklist first published in June 2025, expected its next edition in September or October 2026.
Facts checked: September 30, 2026.
Recent changes at a glance
| When | What changed | Decided by | What it means for most US birders |
|---|---|---|---|
| July 2024 | Hoary and Lesser Redpoll merged with Common Redpoll, now just Redpoll | AOS | One fewer species if you'd counted two redpolls |
| August 2025 | Herring Gull split into four species | AOS | Usually no change: yours is now American Herring Gull |
| August and October 2025 | Warbling Vireo split into an eastern and a western species | AOS, then eBird/Clements (not AviList) | One more species if you've seen both |
| October 2025 | Yellow Warbler split in two | eBird/Clements; ABA in January 2026 | Usually no change: yours is Northern Yellow Warbler |
| October 2025 | Whimbrel split in two | eBird/Clements; ABA in January 2026 | Usually no change: yours is Hudsonian Whimbrel |
The details of each are below.
What is a split?
A split is when scientists decide that what was treated as one species is really two or more. Each new species gets its own name, and each can go on your list on its own.
Splits come from new evidence. When the American Ornithological Society (AOS) split Herring Gull in 2025, it pointed to differences in genes, appearance, ecology and voice.
If you've already seen both of the new species, a split can add a bird to your list without a new sighting.
What is a lump?
A lump is the reverse: two or more species are merged into one, because the evidence says they belong together. If you had counted both, your list goes down by one.
Recent examples
Herring Gull became four species (2025)
In August 2025 the AOS split Herring Gull four ways: American Herring Gull, Vega Gull, European Herring Gull and Mongolian Gull. According to Kenn Kaufman in Audubon magazine, American Herring Gull is the one to expect almost everywhere in North America. Vega Gull is the common one in parts of western Alaska. European Herring Gull is a very rare visitor to eastern Canada, and Mongolian Gull lives in Asia.
So for most US birders, the gull in their notebook is now called American Herring Gull, and the count doesn't change. Someone who has also seen a Vega Gull in Alaska gains a species.
Yellow Warbler and Whimbrel (2025)
In October 2025, eBird's checklist (Clements) split two familiar birds:
- Yellow Warbler became Northern Yellow Warbler and Mangrove Yellow Warbler.
- Whimbrel became Hudsonian Whimbrel and Eurasian Whimbrel.
The ABA added all four to its checklist in January 2026. Northern Yellow Warbler and Hudsonian Whimbrel are the common ones here. Mangrove Yellow Warbler breeds in the Florida Keys and locally in Texas, and Eurasian Whimbrel is a rare visitor.
Names can differ even when checklists agree on the species. AviList, the new global checklist, calls the same two warblers American Yellow Warbler and Mangrove Warbler.
The redpolls became one (2024)
In July 2024 the AOS lumped Hoary Redpoll and Lesser Redpoll with Common Redpoll. There is now one species, called simply Redpoll. Kaufman noted that birders no longer have to decide whether a pale bird is pale enough to count. If you had both Common and Hoary on your list, your total dropped by one.
When checklists disagree: Warbling Vireo
The AOS (August 2025) and eBird/Clements (October 2025) both split Warbling Vireo into an eastern and a western species. AviList's current edition, v2025b (June 2026), still treats it as one. Same birds, same sightings, but a different total depending on the checklist.
Why your total changes by itself
As eBird's help puts it, "new splits or lumps are regularly justified." Checklists are updated on a schedule:
- eBird updates its taxonomy once a year, in October.
- The AOS publishes yearly supplements to its North American checklist. The last two came out in July 2024 and August 2025.
- AviList plans one edition a year; its June 2026 update said the next one was due in September or October 2026.
So as we write this, at the end of September 2026, the next round of changes is only weeks away.
When an update arrives, apps such as eBird apply it to your old records for you. eBird's help page explains one catch. If you logged a bird under a recognizable subspecies group, the record moves neatly to the matching new species. If you logged it only under the old species name, it may become an "either/or" record, which doesn't count as a species.
A tip for the future: when your app lets you record a recognizable form, and you're sure which one you saw, record it. eBird's own example is Yellow-rumped Warbler, which you can log as "Myrtle" or "Audubon's".
Which checklist is right?
None of them is wrong. A checklist is the best scientific judgment at the time, and it changes as evidence comes in.
AviList was launched in June 2025 to bring the world's main checklists together. Its partners include the AOS, the Cornell Lab of Ornithology, BirdLife International, the International Ornithologists' Union and Avibase. The IOC World Bird List has stopped at version 15.2, and eBird/Clements is making final changes through 2026 to line up with AviList. So we expect the totals in different apps to drift closer together over time.
For what these changes mean for the total number of species in the US and Canada, see how many bird species are in the US and Canada.
How our books handle it
Birdfolio matches every record in your file to a species on AviList (version v2025b as we write this), and we credit AviList in every book. Here's what that means for you:
- Familiar names. Where AviList lists the eBird name for a species, we print that one. You'll see "Northern Yellow Warbler", as in your eBird list.
- Older names are placed for you. eBird and iNaturalist files include scientific names, which let us place older records. A Hoary Redpoll (Acanthis hornemanni) in your file goes under Redpoll. A notes page in the book lists every change like this. Before you order, the preview shows the same list under "Name changes we handled".
- Uncertain records are kept, not counted. A "gull sp." or a "Greater/Lesser Yellowlegs" appears on an "also recorded" page, not in your species total.
- No guessing. If we can't match a name, which can happen with an old name in a typed list, the preview tells you. You can then check the spelling or use today's name.
Because of cases like Warbling Vireo, your book's total can occasionally differ from your app's. When it does, the notes page shows exactly why.
To see how a finished book looks, page through a Birdfolio. For the basics, start with what is a life list?
Birdfolio is not affiliated with eBird, the Cornell Lab of Ornithology or iNaturalist.