Once considered common throughout much of the Sierra Nevada, the Willow Flycatcher (Empidonax trailii) has declined precipitously since the middle of the twentieth century. By the late 1990s the region’s population was estimated at just 300-400 individuals. Willow Flycatchers appear to have stopped breeding at many historically occupied meadows south of Lake Tahoe and 6% annual declines in population size are reported for the area between the south fork of the Feather River and Lake Tahoe. Recent studies suggest one explanation of the decline is poor nesting success, largely due to meadow desiccation, which allows mammalian predators easier access to Willow Flycatcher nests.
Causes of meadow desiccation throughout the Sierra Nevada include streambank erosion due to livestock grazing and road construction, water diversions, climate change, and other factors. Yet, many of these factors would appear to play little if any role within the confines of Yosemite National Park, where IBP research has documented that the species has stopped breeding in recent decades.
IBP’s work on Willow Flycatcher in the Sierra Nevada is focused on understanding causes of the population decline, assessing the current status of the species throughout the region, and identifying and facilitating opportunities for restoration and conservation.
For more information about IBP’s work with Willow Flycatchers, please contact Helen Loffland
Photo Credits: Top, Kelly Colgan Azar; Right Column Bottom, Kelly Colgan Azar