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<oai_dc:dc xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:oai_dc="http://www.openarchives.org/OAI/2.0/oai_dc/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.openarchives.org/OAI/2.0/oai_dc/ http://www.openarchives.org/OAI/2.0/oai_dc.xsd">
  <dc:contributor>Barbara E. Kus</dc:contributor>
  <dc:creator>Scarlett L. Howell</dc:creator>
  <dc:date>2024</dc:date>
  <dc:description>&lt;html&gt;&lt;body&gt;&lt;p&gt;We surveyed for Southwestern Willow Flycatchers (&lt;i&gt;Empidonax traillii extimus&lt;/i&gt;; 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. There were a minimum of 74 territorial flycatchers detected at 1 location (VLH), and 12 transient flycatchers of unknown subspecies detected at 2 locations (CNF and VLH). At VLH, we detected a minimum of 31 males, 40 females, and 3 flycatchers of unknown sex. In total, 51 territories were established, containing 40 pairs and 11 flycatchers of undetermined breeding status (8 males and 3 flycatchers of unknown sex). Of the 40 pairs, 9–11 pairs were monogamous (1 male and 1 female), and 29–31 pairs were polygynous (1 male paired with more than 1 female). For the first time since annual surveys began in 2015, no territorial flycatchers were detected downstream from Lake Henshaw. Brown-headed cowbirds (&lt;i&gt;Molothrus ater&lt;/i&gt;; cowbird) were detected at all four survey locations. No banded flycatchers were detected during surveys.&lt;/p&gt;&lt;p&gt;Flycatchers used three habitat types in the survey area: (1) mixed willow riparian, (2) willow-cottonwood, and (3) oak-sycamore. Of the flycatcher locations, 86 percent were in habitat characterized as mixed willow riparian, and 95 percent were in habitat with greater than 95-percent native plant cover. Exotic vegetation was not prevalent in the survey area.&lt;/p&gt;&lt;p&gt;There were five nests incidentally located during surveys: one failed, one was seen with eggs on the last visit, and the outcome of the remaining three nests was unknown. One of these nests was parasitized by cowbirds, and a second nest was suspected to contain a cowbird nestling. Adult flycatchers in two territories were observed feeding cowbird fledglings. No juvenile flycatchers were detected during surveys.&lt;/p&gt;&lt;/body&gt;&lt;/html&gt;</dc:description>
  <dc:format>application/pdf</dc:format>
  <dc:identifier>10.3133/dr1194</dc:identifier>
  <dc:language>en</dc:language>
  <dc:publisher>U.S. Geological Survey</dc:publisher>
  <dc:title>Distribution and abundance of Southwestern Willow Flycatchers (&lt;i&gt;Empidonax traillii extimus&lt;/i&gt;) on the Upper San Luis Rey River, San Diego County, California—2023 data summary</dc:title>
  <dc:type>reports</dc:type>
</oai_dc:dc>