no sexual dimorphism; eye-ring, wingbars (California, USA; 2007-02-03)

Grey Flycatcher
Empidonax wrightii

Native Range: North America

Notes: this is another in a large group of small-sized Empidonax flycatchers that constitute a "sibling-species" complex, meaning that the species are nearly impossible to tell apart from one another in the field by plumage and morphology alone; instead, identification to a particular species relies on a combination of clues including habitat, subtle plumage features, behaviors in some cases, and especially the species' distinctive songs (which originally gave biologists the best hint that multiple species were present). This western species offers a unique behavioral cue for its identification: when perched, it consistently pumps its tail downward.

grey all over; pumps tail downward (California, USA; 2007-02-03)