Walking the road to Mexil a birdy movement caught my eye, I focused on my quarry, and groaned. Groaned, because it was one of those small, mousy-gray, white wingbared, white eyeringed, tail-flicking, flycatchers of the genus EMPIDONAX, and the genus Empidonax is notorious for its many look-alike, hard-to-identify species. If they're not singing, sometimes in the field you just have to forget about getting a positive ID, and nowadays migratory birds in the Yucatán aren't singing. You can see my drably colored ambiguity below:
Actually, the Empidonax problem isn't as bad in the Yucatan as it is in much of Mexico. Howell's distribution maps in A Guide to The Birds of Mexico and Northern Central America indicate that among the Empidonax in the Yucatan only the Least Flycatcher overwinters, while the Yellow-bellied, Acadian and possibly the Alder and Willow Flycatchers pass through as they continue farther southward. Fourteen Empidonax species are listed for Mexico.
If I had to guess, I'd say that the bird in the picture is the Least Flycatcher, EMPIDONAX MINIMUS. Its eyering is especially bold, plus its throat isn't particularly white, and maybe it even has a wider- than-normal beak, all Least traits.
Howell writes that the Least "holds tail slightly below body plane; after tail flicks, tail wobbles slightly, unlike most Empidonax where tail usually stops after a discrete flick." You can see the "tail slightly below body plane" in the picture, plus that wobble after the tail flick is something to see! I'd never noticed that.
The most important evidence that it's a Least, however, is that only Leasts definitely overwinter here, and at this time of year the other species may be passing through but seldom would they be as common as the Leasts. None of these features enable me to ID the bird with certainty, however -- not until the song is heard.
During the North American summer Least Flycatchers occur over much of Canada and the northern US where they show up in scrub, along woods edges and orchards.