Eastern Kingbirds are monogamous. If the pair survives their winter sojourn to South America, they usually remate and use the same territory. “Nevertheless,” write Murphy (1996), “extra-pair copulations and intraspecific brood parasitism may be common.”
Pairs only raise one brood of young per year. One reason for single brooding may be that catching enough flying insects to raise a brood is difficult, especially during cool, wet summers. The result is an extended period of parental care.