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We surveyed for Southwestern Willow Flycatchers (Empidonax traillii extimus; flycatcher) at 33 locations along multiple drainages in San Diego County, including portions of Agua Hedionda Creek, Cottonwood Creek, Escondido Creek, Los Penasquitos Creek, Otay River, San Diego River, San Dieguito River, San Luis Rey River, Sweetwater River, and Tijuana River. Resident flycatchers were only found on two drainages in San Diego County, at San Dieguito and San Luis Rey Rivers, with 99 percent occurring on the San Luis Rey River. Resident flycatchers were detected at 18 percent of survey locations (Bonsall, Cleveland National Forest, Rey River Ranch, San Dieguito, and Vista Irrigation District [VID], and VID Lake Henshaw). Resident flycatchers were documented for the first time at Lake Henshaw, the only new location surveyed that supported flycatchers. We detected a minimum of 80 resident flycatchers from 2015 to 2019, most of these were upstream and downstream from Lake Henshaw. Transient flycatchers were found at 42 percent of survey locations; 38 transient individuals were detected at Agua Hedionda Creek, Otay River, San Diego River, San Dieguito River, and the San Luis Rey River. Over the course of this study, 11 locations historically occupied by resident flycatchers were resurveyed; only 5 were found to have resident flycatchers: (1) Bonsall, (2) Cleveland National Forest, (3) Rey River Ranch, (4) San Dieguito, and (5) Vista Irrigation District. The number of resident flycatchers declined from previous high counts at all five locations. Collectively, the number of resident flycatcher territories within the historically occupied area of the upper San Luis Rey River downstream from Lake Henshaw (Cleveland National Forest, Rey River Ranch, and Vista Irrigation District) declined 71 percent between 1999 (48) and 2019 (14); 42 percent of the decline occurred between 1999 and 2016, with an additional decline (50 percent) occurring between 2016 and 2019. In 2016, the distribution of flycatcher territories at the historically occupied area of the upper San Luis Rey River changed relative to the distribution in 1999: the proportion of territories at Cleveland National Forest and Rey River Ranch decreased to 36 percent each, while Vista Irrigation District increased to 29 percent, creating a more equal distribution of territories across the historically occupied area. By 2019, the distribution changed relative to 2016, with most of the territories spread equally bet

We surveyed for Southwestern Willow Flycatchers (Empidonax traillii extimus; flycatcher) along the upper San Luis Rey River near Lake Henshaw in Santa Ysabel, California, in 2021. Surveys were completed at four locations: three downstream from Lake Henshaw, where surveys occurred from 2015 to 2020 (Rey River Ranch [RRR], Cleveland National Forest [CNF], Vista Irrigation District [VID]), and one at VID Lake Henshaw (VLH) that has been surveyed annually since 2018. There were 78 territorial flycatchers detected at 3 locations (RRR, CNF, VLH), and 1 transient flycatcher of unknown subspecies was detected at VID. Downstream from Lake Henshaw, five flycatchers, including three males and two females, were detected at RRR and CNF. In total, three territories were established, consisting of two pairs and one male of undetermined breeding status. At VLH, we detected 73 flycatchers, including 32 males, 38 females, and 3 flycatchers of unknown sex. In total, 43 territories were established, containing 38 pairs (22 monogamous pairings, 7 confirmed polygynous groups consisting of 7 males each pairing with 2 different females, and 1 suspected polygynous group consisting of 1 male and 2 females), and 5 flycatchers of undetermined breeding status (2 males and 3 flycatchers of unknown sex). Brown-headed cowbirds (Molothrus ater; cowbird) were detected at all four survey locations. Flycatchers used five habitat types in the survey area: (1) mixed willow riparian, (2) willow-cottonwood, (3) willow-oak, (4) willow-ash, and (5) sycamore-oak. Eighty-seven percent of the flycatchers were detected in habitat characterized as mixed willow riparian, and 94 percent of the flycatchers were detected in habitat with greater than 95-percent native plant cover. Exotic vegetation was not prevalent in the survey area. There were 15 nests incidentally located during surveys: 1 was successful, 2 were seen with eggs or nestlings on the last visit, 9 failed, and the outcome of the remaining 3 nests was unknown. Three of these nests were parasitized by cowbirds. There were 13 juveniles detected at VLH during surveys; no juveniles were detected at RRR or CNF. Of the 10 banded flycatchers detected during surveys, 7 were resighted and confirmed to be adults that held territories in previous years. Three flycatchers with a single dark blue federal band, indicating that they were banded as nestlings in the former demo