San Diego Management & Monitoring Program


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2001 2001 Upper San Luis Rey River and PAMO Valley Brown-headed Cowbird Control Program report

Lead author: Jane C. Griffith
A trapping program was implemented along the upper San Luis Rey River (uslr) and Pamo Valley (pv) in San Diego County, California, to protect nesting southwestern willow flycatchers (Empidonax trail/ii extimus, flycatcher, swfl), least Bell's vireos ( Vireo bellii pusillus, vireo, lbvi), and riparian cohabitants from brood parasitism by the brown-headed cowbird (Molothrus ater). Four traps were operated in each location (8 total) from 1 April to 30 June 2001. We removed 284 cowbirds (68 males, 42 females, and 1j 11veniles at 11slr; 103 males, 60 females, and 10juveniles at pv). In addition, 290 individuals of 8 non-target species were captured (47 at uslr, 243 at pv), of which all but 2 (0.7%) were released unharmed. Topical protection from cowbird parasitism allows targeted populations of host species to increase annual productivity and to grow, but does not affect the regional cowbird population (Griffith and Griffith 2000).

2003 2003 Upper San Luis Rey River and PAMO Valley Brown-headed Cowbird Control Program report

A trapping program was implemented along the upper San Luis Rey River (uslr) and Pamo Valley (pv) in,San Diego County, California, to protect nesting southwestern willow flycatcher (Empidonax traillii extimus, flycatcher, swfl), least Bell's vireo ( Vireo bellii pusillus, vireo, lbvi), and their riparian cohabitants from brood parasitism by the brown-headed cowbird (Molothrus ater). Four traps were operated in each location (8 total) from 1 April to 30 June 2003. We removed 207 cowbirds (54 males, 38 females, and 0 juveniles at uslr; 61 males, 48 females, and 6 juveniles at pv). In addition, 330 individuals of 8 non-target species were captured (79 at uslr, 251 at pv), of which all but 6 (l.8%) were released unharmed. Topical protection from cowbird parasitism allows targeted populations of host species to increase annual productivity and to grow between years, but does not affect the regional cowbird population (Griffith and Griffith 2000).