An energetic forager, Bell’s vireo searches for its invertebrate prey while hopping between branches, often flicking or bobbing its tail as it goes (2) (4). Bell’s vireo often flicks its wings while eating, and will take larger, hard-bodied prey to a branch and hammer it with its bill before consuming it (2) (4). A pair may forage together during the breeding season, spiralling up the vegetation, gleaning insects as they go. During the breeding season, the prey of Bell’s vireo includes beetles, grasshoppers, moths, caterpillars and small spiders. Prey is also sometimes captured in flight (2).
Bell’s vireo typically begins nesting in April, with nesting usually continuing through to July (2) (7). The male will establish and defend a territory, using high intensity singing to warn off rivals, although physical conflict may also occur. Singing begins before sunrise and continues persistently throughout the day (2).
Courtship and pair-bonding behaviour in Bell’s vireo involves aggression directed toward the female, mid-air chases, posturing and calling. Bell’s vireo pairs tend to be monogamous, although birds may switch mates from year to year, and occasionally between breeding attempts within the same year. Both adults share the nest building and incubation duties, although the female may incubate the eggs more often during the day, and always at night. The nest is an open, basket-like cup structure made of grass, straw-like stems and other plant material. It is often suspended from the forks of low branches, about one metre above the ground, and is decorated with spider egg cases (2).
Typically, 3 to 4 eggs are laid, and the chicks hatch after around 14 days. Bell’s vireo hatchlings are naked and pink, and take around 10 to 12 days to develop feathers and fledge. If the pair does not manage to successfully rear the young to fledging, they may re-nest, with pairs making up to seven nesting attempts per season (2). Bell’s vireo may be vulnerable to nest predation by a number of species, including ants, snakes, birds and mammals, such as rats (2).