While going through thousands of images taken over the last month, I came across a bird that I could not identify. It was photographed at Hammonasset Beach State Park on May 14.
It's an Empidonax flycatcher that I thought was a Willow Flycatcher when I saw it, perhaps because they are resident birds, commonly seen and heard there in the spring and summer. The problem is that it wasn't singing, and I was busy trying to photograph it so I didn't study the details (not that I would be confident identifying it based on sight alone anyway). After reviewing the following two marginal images, I'm not sure the bird was a Willow Flycatcher.
The bird in the picture has a brighter and more prominent eye-ring than Willow Flycatchers are supposed to. Based on field guide descriptions of the eye-ring, head shape and wing projection, I think Acadian Flycatcher can be eliminated. It looks a bit too elongated, with a longer bill than a Least Flycatcher, which leaves the Willow /Alder (virtually identical) Traill's Flycatcher conundrum. If anyone feels more confident calling it or has a better educated guess than I do, please let me know.
Here are some reference shots of the four species;