Simple technique for distinguishing Yellow-bellied Flycatchers from Cordilleran and Pacific-slope flycatchers

• Published in: Journal of field ornithology 2014-12, Vol.85 (4), p.391-396
• Main Authors: Baumann, Matthew J., Galen, Spencer C., Pederson, Nicholas D., Witt, Christopher C.
• Format: Article
• Language: English
• Subjects: Animal wings; Biological taxonomies; Bird watching; Birds; Empidonax; Feathers; Flycatchers; Linear regression; misidentification; Mitochondrial DNA; mtDNA; Ornithological Methods; Ornithology; Plumage; vagrant birds; Western flycatchers
• ISSN: 0273-8570; 1557-9263
• DOI: 10.1111/jofo.12078

Flycatchers of the genus Empidonax are readily misidentified in the field, in the hand, and even in museum collections. We describe a novel plumage feature that can be used to distinguish Yellow-bellied Flycatchers (E. flaviventris) from the two species that comprise the Western Flycatcher complex, Cordilleran Flycatchers (E. occidentalis) and Pacific-slope Flycatchers (E. difficilis). The length of the buffy fringing on the anterior edge of each secondary feather, visible on the folded wing, is significantly shorter in Yellow-bellied Flycatchers than in Western flycatchers, with minimal overlap. A definitive identification can be made using a simple formula that includes measurements of wing chord and the length of the buffy fringing along the outer edge of the first secondary (S1). This method provides definitive in-hand identification, and the difference in length of the buffy fringing on the secondaries is also a useful field mark for visual identification. Testing our method with 113 museum specimens that had been identified a priori based on locality, we correctly identified 112 specimens. The exception was a specimen from Illinois that had been assumed to be a Yellow-bellied Flycatcher. However, based on our formula, it was a Western flycatcher and analysis of its mtDNA sequence confirmed this result, proving the utility of our method. Los tiránidos del genero Empidonax son constantemente mal identificados en el campo, en mano, y aún en colecciones de museo. Describimos un novedoso carácter de plumaje que puede ser usados para distinguir al Mosquetero vientre amarillo (E. flaviventris) de las otras dos especies que comprenden el complejo Mosqueteros del oeste, el Mosquetero cordillerano (E. occidentalis) y el Mosquetero californiano (E. difficilis). El largo de la franja difusa en el borde anterior de cada pluma secundaria, visible cuando el ala está plegada, es significativamente más corta en el Mosquetero vientre amarillo que en los Mosqueteros del oeste, con un solapamiento mínimo. Una identificación definitiva puede hacerse usando una simple fórmula que incluye medidas del largo del ala y del largo de la franja difusa a lo largo del borde externo de la primera secundaria (S1). Este método provee identificación definitiva en mano, y la diferencia en el largo de la banda difusa en las secundarias es también una marca útil en el campo para la identificación visual. Al poner a prueba nuestro método con 113 especimenes de museo que han sido identific