Willow Flycatcher (Empidonax traillii)
The Willow Flycatcher has declined precipitously in the Sierra Nevada since the middle of the twentieth century. Once considered common throughout much of the Sierra Nevada, the Sierra population was estimated to have dwindled to just 300-400 individuals in the late 1990s. Willow flycatcher populations across the West are facing serious declines based largely upon habitat loss and destruction.
The loss of dense willow in meadows is thought to be the principal reason for the reduction of willow flycatcher population and the contraction of its range. This loss of meadow habitat leads directly to poor nesting success due to lack of nesting habitat and also because this reduction allows predators easier access to willow flycatcher nests. The degradation of meadow habitat is also a major problem for the species and this arises from trampling by livestock, road construction, recreation activities, adjacent timber harvests or fuels treatments, fire suppression, water diversions, mining, lodgepole pine encroachment, water diversion and hydroelectric development, and climate change.
Inappropriate and excessive livestock grazing directly impact willow flycatcher populations and habitat by trampling and knocking over nests in willow thickets, altering the vegetation and hydrology of montane meadows, consuming the lower branches and shrub layers of streamside vegetation, consuming or trampling willow and other riparian plants, reducing water quality, compacting soils, and accelerating streambank erosion. Heavy and long term grazing by non-native livestock has resulted in the transforming of what were once richly diverse Sierran meadows into severely impacted livestock pastures dominated by a few non-native grasses and coarse sedges.
Cowbird parasitism is also a significant threat to the willow flycatcher due to its tendency to lay eggs in willow flycatcher nests. Once this egg hatches the young cowbird forces the eggs of the willow flycatcher or newly hatched young out of the nest. Cowbirds are drawn to the type of heavily impacted and grass dominated landscapes where livestock are permitted to dominate.
Willow flycatchers require deep standing or running water near dense large patches of willow (5 to 6 feet tall) for breeding (USDA 2001 SNFPA pg.144 ). In the Sierra Nevada, willow flycatchers successfully breed only in meadows that contain willows of at least 10 acres in size with 50 to 60 percent dense willow cover.
Wet meadows of the Sierra Nevada are a critical resource for the rare willow flycatcher and for many other breeding birds. These meadows are typically managed for livestock production, often to the detriment of wildlife. Fencing stream and meadow areas to prevent the entry of cattle on these sensitive lands, coupled with monitoring and restoration, and in some cases removal of cows, as provided in the original Sierra Nevada Framework of 2001, are sound protection measures to help willow flycatcher populations survive. The Framework revisions of 2004 removed many of the restrictions on grazing, increased grazing in some cases, and does not provide the protection needed to allow this species to recover. The critical status of the willow flycatcher warrants reducing or excluding livestock grazing and other land uses adversely affecting montane meadows and riparian habitat, particularly where there are known flycatcher territories, unless new research can show the land uses have no detrimental effects on the flycatcher and other species. Developments which attract cowbirds such as campgrounds should be kept away from riparian areas to minimize the impacts of the cowbirds on willow flycatchers and other species nesting in willow thickets of mountain meadows.
The willow flycatcher is a Forest Service sensitive species, a U.S. Fish and Wildlife Service species of concern, and has been listed as an endangered species by the State of California since 1990. Currently, half of the California breeding population of the willow flycatcher is in the Sierra Nevada. According to the USFS, the Sierran subspecies of the willow flycatcher has the highest priority for conservation because of their high potential for extirpation from the Sierra (USDA 2001 SNFPA pg.143). Meadow habitat loss is a primary threat to this subspecies (Harris et al 1986; Valentine et al. 1988; USDA SNFPA 2001). Federal forests in California currently listing the species as a management indicator species are the Eldorado, Modoc, Sierra, Stanislaus, and Tahoe National Forests and the Lake Tahoe Basin Management Unit.
Cocimano, M.C., M.L. Morrison, H.A. Mathewson, and L.M. Vormwald. 2011. The influence of meadow moisture levels on activity of small mammal nest predators in the Sierra Nevada, California. Northwestern Naturalist, 92(1):50-56. (273 KB PDF)
Green, G.A., H.L. Bombay, and M.L. Morrison. 2003. Conservation Assessment of the Willow Flycatcher in the Sierra Nevada. Foster Wheeler Environmental Corporation and the University of California. (431KB PDF)
Mathewson, H.A., M.L. Morrison, H.L. Loffland, and P.F. Brussard. 2013. Ecology of willow flycatchers (Empidonax traillii) in the Sierra Nevada, California: effects of meadow characteristics and weather on demographics. Ornithological Monographs 75(1-32). (2.38 MB PDF)
California Department of Fish and Game Natural History Information (URL) --This California state website contains rather limited and old information but is a good basic background composite for the species. Choose from a drop-down list to select the animal you are interested in.