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Brown-Headed Cowbirds and Willow Flycatchers

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Brown-Headed Cowbirds and Willow Flycatchers Brown-headed Cowbirds and Willow Flycatchers NaturalNatural HistoryHistory ofof CowbirdsCowbirds EffectsEffects onon WillowWillow FlycatcherFlycatcher ManagementManagement IssuesIssues BROWN-HEADED COWBIRD (Molothrus ater) BROWN-HEADED COWBIRD (Molothrus ater) Natural History of Cowbirds BroodBrood--parasiteparasite ExpansionExpansion ofof DistributionDistribution Cowbird colonization of the Far West, Rothstein 1994 Natural History of Cowbirds MigratoryMigratory andand ResidentResident BreedingBreeding SeasonSeason Natural History of Cowbirds Breeding Season Early AM activity Nest parasitism Prolific egg-layers Parasitize open-cup nesters Separate feeding and breeding areas Cowbird Abundance & Parasitism Rates Kern River Population 1.0 0.8 0.6 0.4 0.2 0.0 Parasitism Rate Parasitism 0 0.5 1 1.5 2 Point Ct Do cowbirds affect Southwestern Willow Flycatchers? Potential Effects of Parasitism on Willow Flycatchers NestNest abandonmentabandonment EggEgg LossLoss NestlingNestling LossLoss PopulationPopulation effects?effects? Parasitism and Desertion rates of parasitized Willow Flycatchers is highly VARIABLE in different regions. Parasitism Desertion Region rate (N) rate (N) Reference California 68% (19) 57% (14) Harris 1991 California 63% (60) 45% (38) Whitfield 1990 New 22% (129) 35% (26) Stoleson & Finch Mexico 1999 Arizona 7% (2034) 36% (14) Paradzick et al. 1999 Potential Effects of Parasitism on Willow Flycatchers NestNest abandonmentabandonment EggEgg LossLoss NestlingNestling LossLoss PopulationPopulation effects?effects? How often flycatcher young are produced in parasitized nests Arizona:Arizona: 44 outout ofof 3131 nestsnests (13%)(13%) California:California: 1818 outout ofof 133133 nestsnests (14%)(14%) Parasitism and SWFL Productivity 5.0 r KERN 4.0 PEN 3.0 2.0 y = - 0.01x + 1.73 Kern 1.0 Number Fledglings per Pai Number Fledglings 0.0 0.0 20.0 40.0 60.0 80.0 Percent of Nests Parasitized Kus et al. 2006 Potential Effects of Parasitism on Willow Flycatchers NestNest abandonmentabandonment EggEgg LossLoss NestlingNestling LossLoss PopulationPopulation effects?effects? Management practices typically prescribed to help populations of endangered host species CowbirdCowbird TrappingTrapping RemoveRemove cattlecattle Management practices typically prescribed to help populations of endangered host species CowbirdCowbird TrappingTrapping RemoveRemove cattlecattle oror livestocklivestock Experiments in Cowbird Removal Programs WIFL populations and Cowbird Trapping-NO PATTERN WIFL Pairs 60 40 20 0 Number of Pairs 1 2 3 4 5 6 Sites w/ trapping NO trapping SWFL Population Size (c) 50 KERN PEN 40 30 20 Cowbird Control Initiated 10 Number of Territories Number 0 1989 1992 1995 1998 2001 2004 Year Southern CA Cowbird Trapping 2004 (Famolaro summary, Sweetwater) Counties:Counties: Riverside,Riverside, Orange,Orange, SanSan BernardinoBernardino andand SanSan DiegoDiego 180180 trapstraps AboutAbout 59005900 cowbirdscowbirds trappedtrapped AboutAbout 730730 EUSTEUST andand HOSPHOSP trappedtrapped AboutAbout 18,350*18,350* NontargetNontarget speciesspecies releasedreleased AboutAbout 200200 NontargetNontarget ‘‘takentaken’’ Possible impacts of cowbird control: EffectiveEffective cowbirdcowbird trappingtrapping removesremoves thethe selectiveselective pressurepressure ofof parasitismparasitism necessarynecessary toto promotepromote thethe selectionselection ofof antiparasiticantiparasitic defensedefense mechanismsmechanisms Economic,Economic, political,political, ethicalethical Cowbird control is effective in reducing parasitism and increasing annual productivity produces population increases in some species is effective only as long as suitable habitat is available Should be thought of as a short-term tool for managing T&E species Management practices typically prescribed to help populations of endangered host species CowbirdCowbird TrappingTrapping RemoveRemove cattlecattle oror livestocklivestock Cowbirds and Livestock Cowbirds on Los Padres NF 2002 Results with Cowbird ‘Chatter’ Playback Not just livestock… InIn aa centralcentral--southernsouthern CaliforniaCalifornia forest,forest, cowbirdscowbirds areare notnot associatedassociated withwith livestocklivestock However,However, cowbirdscowbirds AREARE associatedassociated withwith passerinepasserine birdsbirds first,first, andand second,second, urbanurban landland--use.use. TheThe availabilityavailability ofof hosthost birdsbirds andand cowbirdcowbird feedingfeeding sitessites likelylikely affectaffect cowbirdcowbird distribution.distribution. SUMMARY CowbirdCowbird effectseffects onon willowwillow flycatchersflycatchers areare sitesite--specificspecific andand temporal.temporal. CowbirdCowbird managementmanagement recommendationsrecommendations mustmust alsoalso bebe sitesite-- specificspecific andand shouldshould bebe reviewed.reviewed. CowbirdCowbird controlcontrol cancan helphelp inin thethe shortshort--term,term, butbut recoveryrecovery ofof SWFLSWFL isis *not**not* dependentdependent onon cowbirdcowbird control.control..
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