Effects of Managed Livestock Grazing on Potential Habitat of Southwestern Willow Flycatchers in West-Central Arizon

The southwestern willow flycatcher (Empidonax traillii extimus ; hereafter SWFL) is an endangered subspecies of willow flycatcher that inhabits dense riparian ecosystems of the southwestern United States. Many factors, including improper livestock grazing practices, are thought to have influenced the decline of this species although few studies have sought to quantify the effects of managed livestock grazing on SWFL habitat. The main goal of my study was to investigate how carefully managed (i.e., time-controlled), seasonal livestock grazing and episodic flooding affected potential SWFL habitat throughout the year. I monitored vegetation responses to livestock grazing in 3 pastures in west--central Arizona throughout 2015 and 2016. The 3 pastures encompassed 17.5 km of a riparian area that was potential habitat for SWFL but was unoccupied. I measured canopy cover (%) of the primary woody plant species; relative biomass (%) of the dominant plant life forms (both herbaceous and woody plants); density (number/m2) of the primary woody seedlings; and relative and total utilizations (%) of herbaceous and woody species. Conservative stocking rates, paired with relatively short seasonal grazing periods that were followed by longer periods of rest, resulted in very light levels of utilization on both herbaceous and woody plants for all sampling periods. Utilization levels were well below the recommended guidelines cited in the USFWS SWFL Recovery Plan for herbaceous and woody vegetation. Species compositions of herbaceous and woody plants were not adversely affected by the grazing management practices implemented in this study. Mean density of woody seedlings declined from 2015 to 2016 mostly in response to 3 consecutive flooding events in late 2015. My results are consistent with previous case studies that have demonstrated that proper livestock grazing practices can be compatible with maintaining SWFL habitat in the southwestern United States.