Does the northern oriole exist or is it the bullock and baltimore oriole seperately?
The Northern is the name for both Bullock and Baltimore. It comes and goes in the literature, because the 2 species are borderline separated. If more than 5% of the animals interbreed, they are considered one species. The orioles (and yellow rumped warblers) were divided in their breeding areas by the great plains. As this area became populated and trees were added, the western and eastern populations began to overlap. The female does have an adversion to a male of the other variety, so they pass the threshold.
