For those people who aren't hard core birders this, along with several other small flycatchers are very hard to tell apart. The best way to tell is by the difference in voice. The onomatopoeic version of this Least Flycatcher voice is a quick "che-bek" usually repeated over and over. For the hard core birders, I couldn't believe the amount of these guys here given we hardly see them on the coast. They were in almost every list I made during this trip.