The Western Kingbird is a conspicuous bird of open habitats that breeds in the western United States and winters in southern Mexico and Central America. It occupies a variety of habitats including riparian forests and woodlands, savannahs, shrublands, agricultural lands (pasture and cropland), deserts, and urban areas. Key features of its breeding habitat include open areas for feeding and trees and shrubs for nesting and perching; human-made structures such as utility poles are also used for nesting. Typical of tyrant flycatchers, this kingbird forages by aerial hawking and perch-to-ground flights, often with acrobatic flying maneuvers. Insects make up the majority of its diet.
This species was originally known as the Arkansas Kingbird, but its name was changed to be more descriptive and to adapt to common usage. Morphologically it resembles Cassin's (Tyrannus vociferans), Tropical (T. melancholicus), and Couch's (T. couchii) kingbirds, but it is distinguished from these species by its smaller bill and the white outer edges of its two outer tail feathers. Its breeding range overlaps considerably with that of Cassin's Kingbird in the southwestern Unites States, but use of different nesting habitats keeps the two species ecologically separate.
The Western Kingbird vigorously defends a small territory around its nest against conspecifics, congenerics, and potential predators. It often mobs hawks and owls that perch or fly nearby. Males are most active in defense, using a harsh buzzing call during attacks. Several nonvocal displays, such as bill-snapping and raising and revealing the red crown feathers, are seen during aggressive behavior. Despite this aggressive nest defense, predation is one of the more significant causes of egg and nestling mortality.
The breeding range of this species has expanded gradually since the late 1800s, when settlers began altering habitats. The Western Kingbird was able to spread eastward across the northern mixed-grass prairies of the Dakotas and southern Canada due to the planting of trees. In other areas, such as Texas, range expansion was made possible by forest clearing and the proliferation of utility poles and wires. Recent survey data indicate that populations are increasing slightly across most of the nesting range.