If there is a group more difficult to identify than the pewees and Empidonax flycatchers (Empids) in the New World, then I don't know it... these members of the Tyrant Flycatchers family are extremely similar, specially here in Panama where most of them occur as long-distance migrants (so often with faded plumages and silent). The "difficult-to-ID" label doesn't apply to all of them... some are quite distinctive, as those residents of Panama's western highlands (check this). In Panama City (central Panama), there is only one resident pewee... the Tropical Pewee.
This species is extremely similar to other migrant pewees... but this one vocalizes frequently (that's how I identified the above individual), thus making it easy to ID. Also notice the pale loreal area (the area between the eye and the base of the bill) and the relatively short primary projection (the length of the wing/primaries beyond the tertials on a resting bird). Compare it with the next species:
VERY similar! Silent birds during migration season are hard to ID, but I also heard this bird, it is an Eastern Wood-Pewee. They become very common in Panama City as passage migrants, where they frequently vocalize as well. Now compare this bird with the next one (that I saw in the same site that this Eastern Wood-Pewee):
First of all, its darker overall color is evident at first glance. However, notice also its straight back. In comparison, the Eastern Wood-Pewee looks hunchbacked. This is a Western Wood-Pewee, which is not that common at all in Panama City during migration. This one didn't vocalize, but with careful observation it can be ID properly. Other field marks to notice are the different wing bars, with a dull upper wing bar and a bright lower wing bar. In Eastern Wood-Pewee, both wing bars are equally bright. Other differences are better appreciated in the next photo of the same individual:
It has a mostly dark lower mandible and a more extensive vest compared to Eastern Wood-Pewee. Other differences in posture, primary projection / tail length ratio and tail angle are not evident in these photos... but at least you can see that it is not absolutely necessary to listen these birds to positive ID them. It is a shame that we can't say the same about identifying Empids... check for example this one, I took the next photo the same day I saw both pewees above:
Prominent wing bars, eye-ring, coloration, behavior and short primary projection identify it as an Empidonax flycatcher (not a pewee)... considering the not-very-prominent eye-ring and size it can only be identified as a member of the former Traill's Flycatcher complex (Alder and Willow Flycatchers). I took the photo last weekend, so both species are expected. Anyone want to try? The only other regularly found Empid in Panama City is the Acadian Flycatcher, which usually favors a different habitat (forest), is smaller and has a more prominent eye-ring... but several other very-similar species have been recorded as vagrants around and close to the city.
The last pewee found in Panama is one relatively easy to identify due to its larger size, large-head look and prominent vest in the underparts, the Olive-sided Flycatcher.
So, are you ready to ID our pewees and Empids?