The diet of the least flycatcher consists predominantly of insects and some spiders, although it also occasionally eats fruits and seeds, particularly in winter. Most foraging takes place from a low perch, from which the least flycatcher will dart out to catch insects in the air. Prey is also plucked from vegetation, often while the flycatcher is hovering (2) (3) (4) (5).
The least flycatcher usually breeds between May and August (2) (4). Males establish and defend small territories, but these are usually grouped together in loose clusters. The least flycatcher can be aggressive towards other species, often chasing them out of its territory (4) (5). The nest is built by the female, usually in the fork of a small tree, and consists of a neat, woven cup of bark, grass, twigs, rootlets, moss, pine needles, spider and caterpillar webs, leaves and other materials. It is lined with fine grass, hair, feathers, plant down and plant stems (2) (3) (4) (5), and even in one case with dragonfly wings (3).
Four yellowish- or creamy-white eggs are usually laid, and are incubated by the female least flycatcher for 12 to 15 days. Both adults feed the chicks, which leave the nest at about 12 to 17 days old and may be fed by the adults for a further 2 to 3 weeks (2) (4) (5). The least flycatcher first breeds at a year old, and has been known to live for over five years (2) (4).
An unusual feature of the least flycatcher’s annual cycle is the very short time it spends on its breeding grounds. The adults leave the breeding areas relatively early, and, unlike most other species, before moulting. This means that the breeding season lasts for no more than about 64 days in total, but it may allow the adults to arrive on the wintering grounds early to establish winter territories (2) (3) (4). Juvenile least flycatchers migrate south later than the adults (2) (3) (4) (5).