Status and Management of the Least Bell’s Vireo and Southwestern Willow Flycatcher in the Santa Ana River Watershed, 2016, and Summary Data by Site and Watershed-wide, 2000-2016 Prepared by The Santa Ana Watershed Association Prepared for Orange County Water District U.S. Fish and Wildlife Service U.S. Army Corps of Engineers Principal Field Investigators and Authors Susan M. Hoffman Richard Zembal Co-Authors and Field Investigators Melody Aimar Maricela Archer Allyson Beckman Cynthia Chavez Jill Coumoutso Nicole Housel Cameron Macbeth Terry Reeser November 2016 Table of Contents ABSTRACT ...................................................................................................................................................... 1 INTRODUCTION ............................................................................................................................................. 1 METHODS ...................................................................................................................................................... 3 Study Location ........................................................................................................................................... 3 Monitored Sites ..................................................................................................................................... 3 San Jacinto ............................................................................................................................................ 4 San Timoteo Canyon ............................................................................................................................. 4 Mockingbird Canyon ............................................................................................................................. 5 Santa Ana River (SAR) - Upstream ........................................................................................................ 5 Norco Bluffs, I-15 to River Rd. ............................................................................................................... 6 Chino Hills .............................................................................................................................................. 7 Santa Ana Canyon ................................................................................................................................. 7 Upper Canyon ........................................................................................................................................ 8 Green River Golf Club ............................................................................................................................ 8 Featherly Regional Park ........................................................................................................................ 9 Sampled Sites ...................................................................................................................................... 10 Temescal Canyon ................................................................................................................................ 10 Incidental Sites .................................................................................................................................... 10 Vireo Monitoring ..................................................................................................................................... 11 Brown-headed Cowbird Trapping ........................................................................................................... 12 RESULTS ...................................................................................................................................................... 14 Vireo Abundance ..................................................................................................................................... 14 Chronology of Breeding Activity .............................................................................................................. 15 Nesting Site Preferences ......................................................................................................................... 15 Predation Rates ....................................................................................................................................... 16 Brown-headed Cowbird Parasitism ......................................................................................................... 16 Repaired Nests ........................................................................................................................................ 17 Results and Discussion by Site ................................................................................................................. 17 Monitored Sites ................................................................................................................................... 17 San Jacinto .......................................................................................................................................... 17 San Timoteo Canyon ........................................................................................................................... 18 Mockingbird Canyon ........................................................................................................................... 20 Santa Ana River (SAR) - Upstream ...................................................................................................... 20 SAR - Riverside Ave. to Van Buren Blvd. .............................................................................................. 21 SAR - Hidden Valley - North (north side of river) ................................................................................. 22 SAR - Hidden Valley - South (south side of the river) .......................................................................... 22 SAR - Goose Creek, Norco to I-15 ........................................................................................................ 23 Norco Bluffs, I-15 to River Rd. ............................................................................................................. 24 Chino Hills ............................................................................................................................................ 25 Santa Ana Canyon ............................................................................................................................... 25 Upper Canyon ...................................................................................................................................... 28 Green River Golf Club .......................................................................................................................... 29 Featherly Regional Park ...................................................................................................................... 29 Sampled Sites ...................................................................................................................................... 31 Temescal Canyon ................................................................................................................................ 32 Incidental Sites .................................................................................................................................... 33 Southwestern Willow Flycatcher ............................................................................................................. 33 Sightings of Interest – Incidental Species Observations .......................................................................... 34 BROWN-HEADED COWBIRD TRAPPING RESULTS ....................................................................................... 34 Brown-headed Cowbird Trapping, March-July 2016 .............................................................................. 34 Non-Target Captures in Cowbird Traps, March-July 2016 ...................................................................... 35 Fall/Winter 2015-2016 Brown-headed Cowbird Trapping and Non-Target Captures ............................ 35 DISCUSSION ................................................................................................................................................. 35 MANAGEMENT RECOMMENDATIONS ........................................................................................................ 37 FUNDING ACKNOWLEDGEMENTS............................................................................................................... 39 ACKNOWLEDGEMENTS ............................................................................................................................... 39 Figure 1. Map of the Santa Ana Watershed. ............................................................................................... 43 Figure 2. Least Bell’s Vireo survey sites in the Santa Ana Watershed, 2016. ............................................. 44 Figure 3. Brown-headed Cowbird trap locations in the Santa Ana Watershed, 2016. ............................... 45 Figure 4. Norco Bluffs Vireo Survey Area. ................................................................................................... 46 Figure 5. Least Bell’s Vireo abundance in the Santa Ana Watershed, including Prado Basin, 2001-2016. 47 Figure 6. Brown-headed Cowbirds removed from sites in the Santa Ana Watershed, 2000-2016. .......... 48 Figure 7. Least Bell’s Vireo territories at four sites in the