This is a planned 5-Year study. USGS will conduct a 2-phased investigation to: 1) document the abundance and distribution of flycatchers in San Diego County; and 2) collect demographic data that will permit an assessment of the San Luis Rey River population within the larger contexts of MSPA and the state. During phase 1, drainage-wide surveys were conducted from Lake Henshaw downstream to College Boulevard in Oceanside between May and August 2015. These surveys were repeated in 2016, focused on sites outside of the San Luis Rey drainage that have historically supported resident southwestern willow flycatchers, including the Otay, Sweetwater, and San Diego Rivers, Santa Ysabel Creek, and Agua Hedionda. Phase 2 demographic data collection through monitoring started in 2016 and continued through 2017. In 2018, the focus is on monitoring flycatcher pairs in the upper San Luis Rey River study area, and banding and re-sighting color-banded flycatchers. Surveys will also be conducted outside the San Luis Rey drainage.