Alder Flycatcher

En bref

Migratrice
  • Scientific Name: Empidonax alnorum
  • Spanish Name: Mosquero de los alisos
  • Famille : Tyrannidae
  • Known Nicknames: Alder Flycatcher, alder flycatcher
  • Average Length: 13–15 cm / 5.1–5.9 in
  • Average Weight: 12–14 g / 0.42–0.49 oz
  • Wingspan: 21–23 cm / 8.3–9.1 in
  • Key Feature: Olive-green upperparts with pale yellowish underparts and a conspicuous white eye-ring
  • Régime alimentaire principal : Principalement insectivore
  • Range: North America (breeds in Canada and northern United States); winters in South America (Colombia to Bolivia)
  • Habitat: Moist shrubby areas, alder and willow thickets, bogs, and edges of wetlands
  • Social Structure: Solitary or loosely territorial during breeding; migrates in loose groups
  • Nesting/Breeding: Open cup nest in a shrub or small tree fork, often near water
  • Statut de conservation : Préoccupation mineure (LC)
  • Évolution démographique : Stable

The Alder Flycatcher (*Empidonax alnorum*) is a small, unassuming songbird that masterfully hides its identity within the notoriously tricky *Empidonax* genus, making it a true challenge for birders to distinguish from its look-alike cousins. Dressed in an olive-brown back, pale whitish throat, and two faint white wing bars, it presents a classic “little green bird” silhouette, but its true special feature lies in its voice: a sneezy, two-part *fee-bee-o* call that is its most reliable identifier, as visual differences from the Willow Flycatcher are nearly impossible in the field. A master of wet, brushy habitats like alder thickets and willow bogs across northern North America, this insectivorous flycatcher perches upright on exposed twigs, sallying out to snatch prey mid-air. Its unique breeding strategy involves building a compact, cup-shaped nest of grasses and bark, often placed in a vertical fork of an alder, where it fiercely defends its territory against rivals with aggressive chases and sharp *whit* notes.

Faits amusants

Despite their seemingly plain olive-brown plumage, the Alder Flycatcher possesses a remarkable vocal trick: their “free-beer” call is so distinctive it’s the primary field mark to separate them from their nearly identical cousin, the Willow Flycatcher. They are also dedicated nest builders, weaving cups of grass and bark that are so tightly bound they can hold water, often placed in dense alder thickets. A quirky behavior is their “wing-flicking” display—a rapid, nervous twitch of both wings while perched, which helps them startle insects into movement. They’ve also adapted to migrate incredibly long distances, wintering in South America as far south as Peru, yet returning to the same exact breeding patch in North America year after year.

Habitats et répartition

The Alder Flycatcher primarily inhabits wet, shrubby environments, especially alder and willow thickets, as well as bogs, marshes, and damp forest edges. It prefers areas with dense, low vegetation near water, such as beaver ponds or streamsides, where it perches on exposed branches to hunt insects. Its breeding range spans across Canada and the northern United States, from Alaska and the Yukon eastward through the boreal forest to Newfoundland and the northeastern U.S. states. During winter, it migrates to South America, occupying similar wet, scrubby habitats in countries like Colombia, Ecuador, Peru, and Bolivia.

Comportements & Reproduction

The Alder Flycatcher is a solitary, territorial bird outside of breeding, with pairs forming only for the reproductive season. Males arrive first on the breeding grounds and establish territories through persistent, harsh “fee-bee-o” songs, often perching conspicuously to defend boundaries from rivals. Courtship involves the male performing short, fluttering flights and chasing the female through dense shrubs, culminating in a brief copulation on a branch. The pair is socially monogamous for a single season, though extra-pair copulations may occur, and they typically raise only one brood per year. A unique reproductive strategy is the female’s construction of a deep, cup-shaped nest placed in a fork of a willow or alder, often over water, which she lines with fine grasses and plant down. She incubates 3–4 creamy, speckled eggs alone for about 12–14 days, while the male defends the territory and brings food. After hatching, both parents feed the nestlings a diet of flying insects, and the young fledge at roughly 13–15 days, becoming independent shortly after, with no further parental care.

Alimentation

The Alder Flycatcher is an insectivorous bird, with its diet consisting almost exclusively of a wide variety of flying insects and other arthropods. It primarily forages by hawking, sallying out from a perch to snatch prey mid-air, but will also glean insects from foliage. Common prey includes flies, moths, beetles, bees, wasps, and caterpillars. Interestingly, while they are highly specialized aerial hunters, they have been observed consuming small berries and seeds during fall migration or in late summer when insect populations decline, though this plant matter makes up a very minor portion of their overall diet. Another notable fact is that they often hunt near water bodies, taking advantage of the high concentration of aquatic insects like mosquitoes and midges that emerge from wetlands.

Couleurs

The Alder Flycatcher is a small, olive-brown bird with a pale yellow to whitish belly, faint wing bars on darker wings, and a subtle pale eye ring. Its throat is whitish, often with a faint olive wash, and it lacks bold markings, relying on muted, streaky plumage that blends into dense, shadowy shrubbery and alder thickets for camouflage.

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