Black-tailed Gnatcatcher
Polioptila melanura
The black-tailed gnatcatcher reaches about 4.5 to 5 inches in length, much of it taken up by a long black tail lined with white outer feathers. The body is blue-grey, with white underparts, and while it is similar to the blue-grey gnatcatcher, the two birds are differentiated by the amount of black in the tail feathers. The male has a black cap during the summer that extends to the eyes. Females and winter males, lacking the black cap, are difficult to distinguish from the blue-grey gnatcatcher.
ID text from Wikipedia, CC BY-SA 4.0
Tropical Gnatcatcher
Polioptila plumbea
The adult tropical gnatcatcher is 10 to 12 cm (3.9–4.7 in) long, and weighs 6 to 8 g (0.21–0.28 oz). Its "jizz" is similar to that of other gnatcatchers; a small bird with a relatively long thin bill, a long frequently cocked tail, grey upperparts and whitish underparts. The central rectrices are black, while the outer are white (consequently, the tail appears primarily black from above, white from below), and there is a white patch in the wing (caused by broad white edging to the tertials).
ID text from Wikipedia, CC BY-SA 4.0
Where you might meet both
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