Tropical Kingbird is a relatively large tyrant flycatcher with a long, slightly notched tail, a gray head with a concealed reddish orange crown patch, grayish olive upperparts, olive chest, yellow underparts, and a slightly notched, brownish black tail. The bill and feet are black.
The range of Tropical Kingbird overlaps in eastern Mexico with that of very similar Couch’s Kingbird (Tyrannus couchii), from which it is best distinguished by voice (see Vocalizations). Tropical Kingbird is slightly smaller than Couch’s Kingbird, but Tropical’s bill is longer (Stouffer and Chesser 1998). Couch’s has paler brown wings and tail and a shallower fork in the tail, although there is considerable overlap between the two species (Traylor 1979a, Zimmer 1985, Pyle 1997).
Cassin’s Kingbird (Tyrannus vociferans) is distinguished from Tropical Kingbird by a dark gray breast band, lighter face, more squared tail, and shorter, thinner bill (Zimmer 1985). Additionally, the outer web of the outermost pair of rectrices is paler than in Cassin’s Kingbirds (Rea 1969).
Western Kingbird (Tyrannus verticalis) is distinguishable from Tropical Kingbird by less extensive and duller yellow underparts and lighter face. The tail of Western Kingbird is usually blacker and more squared (Zimmer 1985), the bill is shorter and thinner (Zimmer 1985), and the outer webs of the outermost pair of rectrices of Western Kingbird are white or yellowish (Rea 1969).
Tropical Kingbird also resembles White-throated Kingbird (Tyrannus albogularis) of South America, but White-throated is smaller, has lighter gray head, and has a yellow (not olive) chest.
Also somewhat similar to Snowy-throated Kingbird (Tyrannus niveigularis) of northwestern South America. Snowy-throated Kingbird is slightly smaller; has darker, more contrasting lores and auriculars (imparting a more "masked" appearance to the sides of the face); it is paler yellow below with a more extensively white throat (i.e., it has a broader, more obvious "bib"); the upperparts are grayer; and tail is square tipped, not notched as in Tropical (see Hilty and Brown 1986, Ridgely and Tudor 1994, and Phillips 1994 for further details).
Adult: Sexes similar, other than in the degree to which the outer primaries are modified (see below). Top and sides of head gray, with dusky auriculars and lores, and a concealed reddish orange crown patch. The back and rump are grayish olive, and the wings are dull brown or blackish. The wing coverts are edged gray; secondaries are edged whitish. The inner webs of the outer primaries of males are distinctly notched, and those of females slightly notched (notches on P6–P10 extend ≥8 mm from tip in males, <8 mm from tip in females; Pyle et al. 1987). Rectrices brownish black; tail slightly notched. Throat grayish white, shading to pale gray on foreneck and olive chest. Rest of underparts yellow, with black bill and feet (Ridgely and Gwynne 1989, Stiles and Skutch 1989, Howell and Webb 1995). Males are slightly larger than females in South America (Jahn et al. 2010b), but otherwise sexes are very similar, except for slight differences noted above.
Immature: Closely resemble adults, but lack or have a reduced crown patch, have brown edges on primary coverts, and lack notches on primaries (Stouffer and Chesser 1998).
Few details are available on molt in Tropical Kingbird, but in the subspecies satrapa in western Mexico, the first prebasic molt occurs on the wintering grounds, primarily September to November, and in later years occurs July to November, while the prealternate molt occurs occurs February to May (Pyle 1997). In Bolivia, birds of the nominate subspecies molt at least part of the body, flight or tail feathers during most months of the year (Jahn et al. 2010d).
Iris: dark brown
Tarsi and toes: black
Bare parts color data from Stouffer and Chesser (1998).
The overall length of males is 18.4–23.0 cm, and of females is 18.5–21.9 cm (Traylor 1979b). The mass of males is 32.0–40.6 g, and of females is 32.7–42.5 g (Dunning 1993). Average (mean) values for adults at Caparú Biological Station in northern Santa Cruz Department, Bolivia, are: wing chord: 111 mm (n = 264); culmen (nare to tip): 18 mm (n = 170); tarsus: 18 mm (n = 77); and mass: 42 g (n = 236; AEJ, unpublished data).