Type: report

Article abstract: 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]).