The 66th Supplement to the AOS Check-list of North American Birds was published today in the journal Ornithology. An excellent summary of all the changes by Michael Retter is at https://www.aba.org/check-list-redux-2025/
As pointed out by Brandon Percival and Nathan Pieplow earlier today, the main change affecting birds in Colorado is the split of Warbling Vireo into Eastern and Western species. The Eastern species occurs on the eastern plains, but also reaches west of I-25 in the northern Front Range. Both can be heard in Boulder County, and an Eastern species individual was singing loudly from the west side of 95th Street when the Anhinga was first found in early June. This split will increase the Colorado state list to 522.
Another important update in this 66th Check-list is that it "catches up" with all the changes that were made to the eBird/Clements checklist in fall 2024. So, another change affecting Colorado birds is the split of Herring Gull into four species: the birds in Colorado are now American Herring Gull. eBird shows that there are two records of Vega Gull from the southeast corner of the Great Salt Lake in Utah. The CBRC has received two reports of Vega Gull in the past, but neither was accepted. However, a Vega Gull in Colorado is a possibility. If Slaty-backed Gull can get here, then so can Vega Gull !!
Other changes in this "catch up" involve bird families and latin names that I will make to the CBRC checklist in the near future.
Cheers, Peter Gent. Chairman CBRC.
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