brown-headed cowbirds and willow flycatchers · 2013. 1. 18. · flycatchers are site-specific and...
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Brown-headed Cowbirds and Willow Flycatchers
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Natural History of CowbirdsNatural History of CowbirdsEffects on Willow FlycatcherEffects on Willow FlycatcherManagement IssuesManagement Issues
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BROWN-HEADED COWBIRD(Molothrus ater)
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BROWN-HEADED COWBIRD(Molothrus ater)
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Natural History of Cowbirds
BroodBrood--parasiteparasiteExpansion of DistributionExpansion of Distribution
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Cowbird colonization of the Far West,Rothstein 1994
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Natural History of Cowbirds
Migratory and ResidentMigratory and ResidentBreeding SeasonBreeding Season
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Natural History of Cowbirds
Breeding SeasonBreeding SeasonEarly AM activityEarly AM activityNest parasitismNest parasitismProlific eggProlific egg--layerslayersParasitize openParasitize open--cup nesterscup nestersSeparate feeding and breeding areasSeparate feeding and breeding areas
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Cowbird Abundance & Parasitism RatesKern River Population
0.00.20.40.60.81.0
0 0.5 1 1.5 2
Point Ct
Para
sitis
m R
ate
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Do cowbirds affect Southwestern Willow Flycatchers?
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Potential Effects of Parasitism on Willow Flycatchers
Nest abandonmentNest abandonmentEgg LossEgg LossNestling LossNestling LossPopulation effects?Population effects?
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Parasitism and Desertion rates of parasitized Willow Flycatchers is highly VARIABLE in different regions.
RegionParasitism
rate (N)Desertion rate (N) Reference
California 68% (19) 57% (14) Harris 1991
California 63% (60) 45% (38) Whitfield 1990
New Mexico
22% (129) 35% (26) Stoleson & Finch 1999
Arizona 7% (2034) 36% (14) Paradzick et al. 1999
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Potential Effects of Parasitism on Willow Flycatchers
Nest abandonmentNest abandonmentEgg LossEgg LossNestling LossNestling LossPopulation effects?Population effects?
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How often flycatcher young are produced in parasitized nests
Arizona: 4 out of 31 nests (13%)Arizona: 4 out of 31 nests (13%)California: 18 out of 133 nests (14%)California: 18 out of 133 nests (14%)
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Kus et al. 2006
Parasitism and SWFL Productivity
0.0 20.0 40.0 60.0 80.00.0
1.0
2.0
3.0
4.0
5.0
Num
ber F
ledg
lings
per
Pai
r
PENKERN
Kern
y = - 0.01x + 1.73
Percent of Nests Parasitized
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Potential Effects of Parasitism on Willow Flycatchers
Nest abandonmentNest abandonmentEgg LossEgg LossNestling LossNestling LossPopulation effects?Population effects?
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Management practices typically prescribed to help populations of endangered host species
Cowbird TrappingCowbird TrappingRemove cattleRemove cattle
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Management practices typically prescribed to help populations of endangered host species
Cowbird TrappingCowbird TrappingRemove cattle or livestockRemove cattle or livestock
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Experiments in Cowbird Removal Programs
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WIFL populations and Cowbird Trapping-NO PATTERN
WIFL Pairs
0204060
1 2 3 4 5 6Num
ber o
f Pai
rs
Sites w/ trapping NO trapping
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SWFL Population Size
(c)
1989 1992 1995 1998 2001 2004
Year
0
10
20
30
40
50
Num
ber o
f Ter
ritor
ies PEN
KERN
Cowbird Control Initiated
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Southern CA Cowbird Trapping2004 (Famolaro summary, Sweetwater)
Counties: Riverside, Orange, San Counties: Riverside, Orange, San Bernardino and San DiegoBernardino and San Diego180 traps180 trapsAbout 5900 cowbirds trappedAbout 5900 cowbirds trappedAbout 730 EUST and HOSP trappedAbout 730 EUST and HOSP trappedAbout 18,350* About 18,350* NontargetNontarget species releasedspecies releasedAbout 200 About 200 NontargetNontarget ‘‘takentaken’’
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Possible impacts of cowbird control:
Effective cowbird trapping removes the Effective cowbird trapping removes the selective pressure of parasitism necessary to selective pressure of parasitism necessary to promote the selection of promote the selection of antiparasiticantiparasiticdefense mechanismsdefense mechanisms
Economic, political, ethicalEconomic, political, ethical
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Cowbird controlis effective in reducing parasitism and increasing annual productivityproduces population increases in somespeciesis effective only as long as suitable habitat is available
Should be thought of as a short-term tool for managing T&E species
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Management practices typically prescribed to help populations of endangered host species
Cowbird TrappingCowbird TrappingRemove cattle or livestockRemove cattle or livestock
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Cowbirds and Livestock
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Cowbirds on Los Padres NF
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2002 Results
with Cowbird ‘Chatter’ Playback
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Not just livestock…In a centralIn a central--southern California forest, southern California forest, cowbirds are not associated with livestockcowbirds are not associated with livestockHowever, cowbirds ARE associated with However, cowbirds ARE associated with passerine birds first, and second, urban passerine birds first, and second, urban landland--use.use.The availability of host birds and cowbird The availability of host birds and cowbird feeding sites likely affect cowbird feeding sites likely affect cowbird distribution.distribution.
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SUMMARYCowbird effects on willow Cowbird effects on willow
flycatchers are siteflycatchers are site--specific and specific and temporal.temporal.
Cowbird management Cowbird management recommendations must also be siterecommendations must also be site--specific and should be reviewed.specific and should be reviewed.
Cowbird control can help in the Cowbird control can help in the shortshort--term, but recovery of SWFL is term, but recovery of SWFL is *not* dependent on cowbird control.*not* dependent on cowbird control.