Although limited in its U.S. distribution, the Tropical Kingbird is a conspicuous, widespread bird, ranging from central Mexico to central Argentina. Found in most climatic regimes—from deserts to wet lowlands to altitudes of more than 3,000 meters—it is common along roadsides and in open areas and appears to thrive in gardens, plazas, and other landscapes modified by humans. It is one of the best-known birds throughout its range because it tends to perch in open view, such as on wires, even in the heat of the day. Its long sallies after flying insects and aggressive chases of potential nest predators also attract attention.
As might be expected, the northern limits of the species' breeding distribution, which lie in the U.S., have changed over time. First discovered nesting near Tucson, Arizona, in 1938, the Tropical Kingbird was reported in succeeding years at other localities in the state. By the 1980s it was breeding regularly only in the lower Santa Cruz Valley. Data collected in the 1990s, however, showed the species breeding extensively in southeastern Arizona and beginning to breed in south Texas, where it resides throughout the year. In addition, nonbreeders (mainly immatures), occur regularly in small numbers along the Pacific Coast of North America, primarily in fall.
The Tropical Kingbird is ecologically and behaviorally similar to its familiar North American congeners, the Eastern (Tyrannus tyrannus), Western (T. verticalis), and Cassin's (T. vociferans) kingbirds. Its U.S. breeding range overlaps with that of the Western, Cassin's, Thick-billed (T. crassirostris), and Couch's (T. couchii) kingbirds in Arizona and Texas. These kingbirds choose similar habitats, although the Tropical may be the most closely associated with human landscapes. Even so, the species often nest near each other, with few overt aggressive interactions ( Phillips et al. 1964a ).
Studies of flycatcher foraging in South America have shown the Tropical Kingbird to be among the most specialized of flycatchers, foraging almost exclusively by sallying after large flying insects (Fitzpatrick Fitzpatrick 1980a , Fitzpatrick 1981 ). This specialization may allow it to overlap with other Tyrannus species, which use other foraging techniques and eat a wider variety of prey. Like its congeners, however, the Tropical Kingbird also regularly supplements its diet with fruit.
Despite its abundance, the Tropical Kingbird has been the focus of little detailed study. Its systematics, both within the species and with Couch's Kingbird, have been difficult to untangle ( Traylor 1979e ). Its general behavior and breeding biology were described by Skutch ( Skutch 1954b , Skutch 1960b ). Its behavior, especially displays and vocalizations, was compared to that of other Tyrannus species by Smith ( Smith 1966d ). Many other aspects of its biology have received only cursory attention. Despite this dearth of basic information, this species would be an ideal one in which to examine geographic variation or how sympatric congeners coexist.