Date: 5/16/19 6:31 am From: Mike Patterson <celata...> Subject: [obol] Re: Malheur empids
I attach the relevant portion of the NAB account below, which roughly translates to: don't fool yourself. It's probably not possible to sort Western Flycatchers in zones of overlap (Eastern Oregon) no matter how nuanced you believe your hearing is...
From: Lowther, P. E., P. Pyle, and M. A. Patten (2016). Pacific-slope Flycatcher (Empidonax difficilis), version 3.0. In The Birds of North America (P. G. Rodewald, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bna.pasfly.03
"Species limits in the E. difficilis complex, which includes both E. difficilis sensu stricto (the Pacific-slope Flycatcher) and E. occidentalis (the Cordillean Flycatcher), are controversial. Despite his extensive, detailed data set and analyses, Johnson 1980b concluded that the only clear species break was between E. difficilis sensu lato and E. flavescens, although he revised this view after allozyme data were available (Johnson and Marten 1988) and then moved to have the species split, a proposal accepted by the American Ornithologists’ Union Checklist Committee (American Ornithologists' Union 1989). Evidence for the split rested on apparent genetic and vocal divergence, yet Phillips 1994c and Pyle 2012 noted that plumage and mensural characters allowed for only a statistical, not a biological, distinction; moreover, evidence for assortative mating is weak, with a mere two pairs documented (Johnson 1994c). Conversely, a mixed population breeds in northeastern California (Johnson 1980b, Johnson 1994c), where “bilingual” birds have been recorded, although even in allopatry songs and calls differ only in certain details (Johnson 1980b)—i.e., they are more similar than different (see Sounds: Vocalizations). Ostensible E. occidentalis at the eastern base of the Cascades in Washington utter Position Notes of E. difficilis sensu stricto (Tweit et al. 1990, Smith et al. 1997), and birds with E. difficilis Position Notes of have been found inland as far east as Missoula, Montana (C. A. Marantz, personal communication). A comprehensive genetic analysis of breeders in the Rocky Mountains of southwestern Canada found hybridization and introgression between the species (Rush et al. 2009c). The existence of hybridization between Pacific-slope and Cordilleran flycatchers raises concern about the decision to split these species; however, the authors also reported that "allopatric populations are genetically distinct in both mitochondrial and nuclear DNA, and the hybridization might not affect populations outside of the contact zone" (Rush et al. 2009c)."