A migratory species, the eastern kingbird heads south for the winter, typically in late July or August (2) (5), with migratory flocks ranging in size from small groups of 5 to 12 birds to thousands of individuals (3). Interestingly, flocks tend to be larger during the autumn migration than during the northwards migration in spring, and social and breeding behaviours are also known to differ between winter and summer. The eastern kingbird returns to its northern breeding grounds in spring, and typically arrives in North America by early to mid-April, although the first birds sometimes arrive as early as March (5).
Aerial courtship has been observed in the eastern kingbird, with the male and female birds often greeting one another with a wing-flutter display (3). The female eastern kingbird is thought to select the nest site (2), and constructs the nest over a period of one or two weeks (2) (3) while the male keeps a look out for predators and competitors (2). Eastern kingbird pairs maintain a breeding territory throughout the summer, which is often used year after year. Males in particular can become very aggressive during territorial disputes, fighting in mid-air with other birds, often interlocking feet with its opponent while doing so. Fighting birds also pull out each other’s feathers. Similar aggression is shown towards large nest predators such as crows (Corvus species) and blue jays (Cyanocitta cristata) (2).
Eastern kingbird nests are constructed high up in the trees (4), and consist of a large, sturdy, open cup (3) built using bark strips, small twigs, dry weed stems and coarse roots (2) (3). The interior of the nest is typically softer, with components including willow catkins (Salix species), cottonwood fluff (Populus species), and cattail down (Typhus species) (2) (3) as well as horse hair (2).
The female eastern kingbird lays eggs between late April and August, with the timing varying depending on the location and individual (3). The eggs of this species are typically oval but are variable in shape, and are generally pale and smooth with an irregular ring of conspicuous reddish spots (2). The size of the clutch varies geographically (5), although typically three to five eggs are laid (2) (4), and usually only one brood is produced per season (2) (5). Incubation is carried out by the female alone (3), and lasts between 14 and 17 days (2) (3). The eastern kingbird chicks are fed by both adults (3) throughout the nestling period, which is typically about 16 or 17 days (2) (3), and for 3 to 4 weeks after fledging (3).
During the breeding season, the eastern kingbird feeds mostly on flying insects (2) (5) such as wasps, grasshoppers, flies and locusts (2), although it may also supplement its diet with fruit (2) (3) (5) including mulberries, blackberries and elderberries (2). Small vertebrates, including frogs, are occasionally taken (2) (3), and these are typically beaten against a perch before being swallowed whole (2). Large insects are also treated in this manner, whereas smaller insects are swallowed as soon as they are captured (2) (5). The eastern kingbird is a sit-and-wait predator (2) which captures most of its prey in flight by sallying from a perch (3) (4) (5). However, it occasionally takes prey from vegetation and the ground, as well as from water (2) (3) (5).
The eastern kingbird eats a lot more fruit during the autumn migration (2) (5), and on the wintering grounds fruit tends to make up the bulk of this species’ diet (2). Fruiting trees often attract large groups of up to thousands of birds (3). Interestingly, the eastern kingbird has rarely been observed drinking, and it is thought to obtain the moisture it requires from the insects and fruit upon which it feeds (2).
The eastern kingbird is known to live for up to ten years or more (2).