Least flycatcher  (Empidonax minimus)

The least flycatcher is classified as Least Concern (LC) on the IUCN Red List (1).

One of North America’s smallest and most common flycatchers, the least flycatcher (Empidonax minimus) is a small, rather drab bird, most easily identified by its characteristic ‘chebec’ song (2) (3) (4). Its plumage is largely brownish-olive to grey, with a whitish throat and whitish underparts. The underparts are washed greyish on the breast and sides and slightly yellowish on the belly. The least flycatcher also has a bold white eye ring, and two white to pale yellow bars on the wings (2) (3) (4).

The least flycatcher’s wings are fairly short and rounded, and its tail is greyish, narrow and slightly notched. Its legs and feet are blackish, and the short bill is black above, with a paler lower mandible (2) (4). The male and female least flycatcher are similar in appearance, while the juvenile has slightly browner upperparts, yellower underparts and more buffy wing bars (2) (3) (4).

In addition to its distinctive ‘chebec’song, the least flycatcher also uses a variety of other calls. The most common is a short, soft ‘whit’, while ‘weep-weep’ notes may be given in aggressive encounters, and quiet ‘churr’ and ‘thrr thrr’ calls are given while nesting. The male least flycatcher also performs flight songs, giving ‘weep’ calls before flying above the trees and giving a range of ‘chebec’ notes and other calls (2) (4).

Flycatchers in the genus Empidonax are notoriously difficult to tell apart. Other than by its song, the least flycatcher can only really be distinguished from related species by its smaller size, greyer plumage, and by small differences in its beak and in the relative lengths of its wing feathers (2) (3) (4) (5).

The least flycatcher breeds across Canada and the northern United States, migrating south to spend the winter in Mexico and Central America, as far south as Costa Rica and central Panama (2) (3) (4) (6). Some individuals also winter in the southern United States, particularly southern Florida (2) (5).

During the breeding season, the least flycatcher inhabits semi-open deciduous or mixed woodland, as well as orchards and shrubby fields (2) (3) (4) (5). It is often found around clearings and woodland edges, but sometimes also in forest interior, in areas with a well-developed canopy (2) (4) (5).

The least flycatcher usually spends the winter in wooded ravines, along woodland edges, in areas of secondary growth, or in pastures, brushland or thickets (2) (3) (4) (5). This species has been recorded at elevations up to around 1,500 metres in Central America (2) (4).

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).

The least flycatcher is a widespread and common species and is not currently considered to be globally threatened (2) (6). Its range may have expanded slightly westward in recent decades (4), but population declines have been noted in other areas (2) (3) (4) (5) (6).

Declines in the least flycatcher population may be due in part to the process of forest succession and increasing forest maturity, which affect the structure of its habitat. It may also be impacted by human alterations to its habitat, including logging, pollution, overgrazing and other disturbances, as well as the loss of forest understory due to high deer densities. Forest die-backs due to acid rain have also been identified as a threat to the least flycatcher in Quebec (2) (4).

There are no known specific conservation measures currently targeting the least flycatcher. Recommended actions for this small bird include preserving large, continuous tracts of suitable forest and minimising the number of forest disturbances, as well as conserving upland forest patches that may serve as important stopover sites during migration (4).

Other proposed conservation measures for the least flycatcher include controlling populations of the white-tailed deer (Odocoileus virginianus) in certain areas, to reduce damage to forest understoreys (4).

The least flycatcher would also benefit from further research into its mating systems, population trends, and its responses to habitat changes. In particular, more information is needed on this species in its wintering grounds and during migration, including on the threats it faces at these times (4).

Find out more about the least flycatcher and its conservation:

• BirdLife International - Least flycatcher:
  http://www.birdlife.org/datazone/speciesfactsheet.php?id=4281
• The Cornell Lab of Ornithology: All About Birds - Least flycatcher:
  http://www.allaboutbirds.org/guide/Least_Flycatcher/id
• Birds of North America Online - Least flycatcher (Empidonax minimus):
  http://bna.birds.cornell.edu/bna/species/099/articles/introduction