Sierra Nevada Willow Flycatcher Decline Continues but Losses Abate at Two Restored Meadows

Abstract

Willow Flycatcher (Empidonax traillii) populations have been declining across the western United States for decades. The Sierra Nevada–southern Cascades population in California is especially vulnerable, with fewer than 200 pairs remaining. Hydrologic restoration has been recommended for conserving this population. Other riparian songbirds have increased in response to restoration, but little is known about how restoration has affected the Willow Flycatcher. The Little Truckee River has long been a stronghold for the Willow Flycatcher, and the demography of the population there was studied intensively from the late 1990s through 2010. Baseline data from that study provided an opportunity to gauge the species’ response to pond-and-plug restoration projects completed at two meadows within the study area in 2009 and 2010. We aggregated and analyzed data from Willow Flycatcher surveys from 1997 through 2019 at the two restored meadows as well as nine nearby unrestored meadows with at least two Willow Flycatcher territories at some time during the demographic study. At most meadows, the number and density of Willow Flycatcher territories declined over the two-decade study period. However, losses at the unrestored meadows were significantly greater than at the restored meadows, where territory density clearly did not collapse following the disturbance caused by restoration and then remained largely stable thereafter. Within large meadows already occupied by Willow Flycatchers, meadow restoration that restores hydrologic function and increases flooding over creekbanks may be an effective strategy for stabilizing declining Willow Flycatcher populations in the Sierra Nevada.