Tanner wrote:
"So here are my questions: What do I need, as a birder in the inland
part of the hybridization zone, in order to confidently identify a pure
Rufous or Allen's hummingbird? Even though Rufous is the default species
on this side of the state line, what does it take to conclusively and
definitively rule out a hybrid? And if one did eventually find a good
candidate for Allen’s this far inland, what is needed to adequately
document it?"
You'd have to capture them and have them in your hand. You may even
need to pull a feather for genetic analysis.
So in other words, you can't. Not with 100% confidence.
Cheers
Dave Lauten
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