As seen on the map below, the Willow Flycatcher has a far-reaching range that extends as far north as Canada and as far south as South America, depending on the time of year (Sogge et al.). The subspecies common to Los Angeles is called the “Southwestern Willow Flycatcher,” or Empidonax traillii extimus. The northern range of this subspecies is limited to the Southwest region of the United States while the southern range is more or less in the vicinity of Costa Rica – a distance of about 4,000 km (Sogge et al.).
A recent USGS report modeled likely habitat locations for the Southwestern Willow Flycatcher across the SW United States. The resulting spatial scale for the species is shown below.
(Hatten 2016)
A historical synopsis of the species in Southern California was written in a 2001 field report titled “Distribution and Abundance of the Southwestern Willow Flycatcher at Selected Southern California Sites in 2001” and published by the USGS. An excerpt follows below:
“Southwestern Willow Flycatchers were once widespread in coastal riparian woodlands of lowland California, and were commonly found in San Diego County, the Los Angeles basin and throughout the San Bernardino/Riverside region. However, survey data indicate that flycatcher populations have experienced significant declines over the past 50 years, with a marked decline from 1965 to 1979 (USFWS 1993). Unitt (1984) estimated that in 1984 the total breeding Willow Flycatcher population in San Diego County numbered fewer than 15 pairs. In response to this decline, the state of California listed the species as endangered in 1992. By 1993, it was estimated that the total flycatcher population in California numbered approximately 70 pairs (USFWS 1993). The U.S. Fish and Wildlife service subsequently listed the Southwestern Willow Flycatcher as endangered in 1995” (Rourke et al).
The reasons for the decline in numbers of the Southwestern Willow Flycatcher “include riparian habitat loss and degradation, cowbird brood parasitism, and the alteration of natural riverine flow regimes associated with the construction of dams and other water projects” (Rourke et al.). Presently, populations of the Southwestern Willow Flycatcher in Southern California “remain small, isolated, and disjunct” (Rourke et al.).
Southwestern Willow Flycatchers typically live in riparian woodland ecosystems near rivers or streams. The following map of Los Angeles provides a perspective on where these ecosystems lie. A larger version can be found at: http://frap.cdf.ca.gov/webdata/maps/los_angeles/fvegwhr_map.19.pdf
(FRAP: Fire Resource Assessment Program)
As seen in the map above, riparian woodlands occur in the western area of the county in the Santa Monica Mountains and in the northern portion of Los Angeles near the border with Kern County. The Southwestern Willow Flycatcher can be found in the dense cover typically offered by riparian woodlands, an example of which is shown below.
(Sogge et al.)
willow flycatcher 