A proposal to split the White-breasted nuthatches into several species was considered by the NACC (checklist Committee) a couple of years ago and not accepted. According to the comments published, they were pretty much in agreement that aculeata should be split, but decided to wait until some issues between the other taxa could be clarified.
In Oregon, there are two populations of White-breasted Nuthatches that can only be distinguished, to my understanding, by calls.
The subspecies I believe that is referred to as using the oak woodland of Oregon, "aculeata" has noticeably different vocalizations than the population found generally on the eastside of the Cascades, the "tenuissima" subspecies.
Awareness of the vocalizations, and habitat preferences, will help distinguish these two populations.
I am not aware that the White-breasted Nuthatch has actually been split, if it has been. But separation in the field is best done by listening to the birds since their plumage and structure are so similar.
I've been recording White-breasted Nuthatch in the Klamath Basin for a numb er of years, partly in anticipation of a future split, but mostly because I enjoy paying attention to bird vocalizations. Both aculeata and tenuissima subspecies are found in the Klamath Basin. I have not yet found a location where both are present.
Kevin Spencer Klamath Falls, OR
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------ Original message------ From: Karen Paulino Date: Tue, Oct 22, 2019 5:34 PM To: [ mailto:<obol...> | <obol...> ] ; Cc: Subject: [obol] Slender-billed nuthatches