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 2020. Surveys were completed at four locations: three downstream from Lake Henshaw, where nest monitoring occurred from 2015 to 2019 (Rey River Ranch [RRR], Cleveland National Forest [CNF], Vista Irrigation District [VID]), and one at VID Lake Henshaw (VLH) that was previously surveyed in 2018 and 2019.
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 2022. Surveys were completed at four locations: three downstream from Lake Henshaw, where surveys occurred from 2015 to 2021 (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.
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 2023. Surveys were completed at four locations: three downstream from Lake Henshaw, where surveys previously occurred from 2015 to 2022 (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.
We surveyed for Southwestern Willow Flycatchers (Empidonax traillii extimus; flycatcher) at select locations along the San Luis Rey River, including along the middle San Luis Rey River near Bonsall and the upper San Luis Rey River near Santa Ysabel, California, in 2024. Surveys were completed at six locations: two along the middle San Luis Rey River (Bonsall [BO] and Rincon), which were last surveyed in 2021, and four along the upper San Luis Rey River, including three downstream from Lake Henshaw that have been surveyed annually since 2015 (Rey River Ranch, Cleveland National Forest [CNF], Vista Irrigation District [VID]), and one upstream at VID Lake Henshaw (VLH) that has been surveyed annually since 2018.
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
We surveyed for Southwestern Willow Flycatchers (Empidonax traillii extimus; flycatcher) at the San Dieguito River and the upper San Luis Rey River in 2025. Surveys were completed at five locations: one along the San Dieguito River (San Dieguito [SD]), which was last surveyed in 2016, and four along the upper San Luis Rey River, including three downstream from Lake Henshaw that have been surveyed annually since 2015 (Rey River Ranch [RRR], Cleveland National Forest [CNF], Vista Irrigation District [VID]), and one upstream at VID Lake Henshaw (VLH) that has been surveyed annually since 2018. There was a minimum of 57 territorial flycatchers (22 male, 35 female) and 3 transient flycatchers of unknown subspecies detected at 1 location (VLH). In total, 37 territories were established, containing 35 pairs (20 males and 35 females) and 2 male flycatchers of undetermined breeding status. Of the 35 pairs, 12 were monogamous pairings, and 23 were polygynous pairings consisting of 3 males each pairing with 2 different females [6 pairs], 3 males each pairing with 3 different females [9 pairs], and 2 males each pairing with 4 different females [8 pairs]).
