Kingbirds (Tyrannus) are aerial-hawking insectivores of open spaces that occur in most physiographic regions of North America. Of the eight species that breed north of Mexico, the Eastern Kingbird is the most widely distributed (Figure 1); it and the Gray Kingbird (T. dominicensis) are the only species of Tyrannus with established breeding populations east of the Mississippi River. Despite its common name, the Eastern Kingbird breeds abundantly west of the Mississippi River, and its range extends to the Pacific Ocean in the state of Washington. In the Great Plains and Far West it may breed sympatrically with one or two other species of kingbirds.
Kingbirds are well known for their aggressive nature. Indeed, Tyrannus means “tyrant, despot, or king,” in reference to their aggressive defense of nests and mates, and their domination of other birds. Pairs are socially monogamous, maintain territories while breeding, and if both survive to the following breeding season, very often reform pair bonds and reuse former territories. Although socially monogamous, extra-pair paternity is widespread as a majority of nests contain young from multiple males (1, 2).
The Eastern Kingbird migrates to western South America and western Amazonia, where most individuals are intratropical migrants during the northern winter (3; D. H. Kim and MTM, unpublished data). While there, most individuals occupy two widely separated locations during the early and late nonbreeding period, and maintain different social and feeding behaviors than during the breeding season. Most individuals travel in flocks and forage on fruit, returning to North America to begin laying eggs between late May and mid June. Clutch size varies geographically (mode of 3–4 eggs), but females raise only a single brood per season. This low productivity is likely related to the species' reliance on flying insects for food; e.g., parents appear to have a difficult time feeding large broods adequately when cool, wet weather reduces the availability of flying insects. The extended period of post-fledging parental care (3–5 weeks) further limits parents to a single brood per year.
The reproductive biology of the Eastern Kingbird has been described in detail by several authors, including early work by Davis in central New York (4) and Montana (5), and later research by Blancher and Robertson (6, 7) in southeastern Ontario, and Murphy in western New York and eastern Kansas (8, 9, 10, 11, 12), central New York (13, 14) and eastern Oregon (15, 16). Vocalizations of Eastern Kingbirds have been described by Smith (17, 18) and Murphy (19, 20), and parental care behavior has been described by Morehouse and Brewer (21) in Michigan, and Murphy and students in central New York (22, 23, 24), and eastern Oregon (25, 26, 27).
The Eastern Kingbird is a widespread species, and although not considered abundant, is typically common. Nonetheless, long-term and ongoing continent-wide negative population trends are cause for concern, a condition shared with many other aerial insectivorous bird species (28).