"Fee-bee-o." This traditional description identifies the song of the Alder Flycatcher. Songs of Empidonax flycatchers, a notoriously difficult group to identify in the field, are the best, and sometimes only, means for determining species. This is especially true for separating the Alder Flycatcher from its sibling species, the Willow Flycatcher (E. traillii). Alder and Willow flycatchers cannot be identified reliably by sight alone, and even in-hand identification is not always certain. Alder (fee-bee-o song) and Willow (fitz-bew) flycatchers were considered one species called Traill's Flycatcher, a name still used to refer to the species pair. Of these two sibling species, the Alder Flycatcher has the more northern and boreal distribution. Alder Flycatchers are late migrants in spring and leave early in the fall; northern populations have a short 70 - 90 day breeding season. This flycatcher is single brooded, although individual pairs may renest after an early loss. Molt occurs primarily on wintering grounds. The Alder Flycatcher is thought to winter chiefly in northern South America (and thus further south than wintering Willow Flycatchers in Middle America and extreme northwestern South America). The only definite winter records for Alder Flycatcher, on basis of call, are from eastern Peru, eastern Ecuador, and northern and eastern Bolivia.