Primary song by a juvenile willow flycatcher

The timing of song development in suboscines, in which song appears not to be
learned from other adults is poorly known. The Willow Flycatcher (Empidonax traillii) is a
suboscine with a primary song typically referred to as fitz-bew. I report here an instance of
very early singing by a 6-8-wk-old Willow Flycatcher, which sang in an aggressive context in
response to a recording of adult flycatcher song. This is exceptionally early development of
primary song, even among suboscines. Early song development may assist in the defense of
winter territories.