Habitat Partitioning by Neotropical Migrant Warblers in the Lower Colorado River Valley

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Introduction
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Objectives

• To determine patterns of neotropical migrant
  warbler migration in Mexico and Arizona along the
  Colorado River corridor.
• To evaluate effects of habitat management
  practices along the Colorado River corridor,
  through comparison of native (Cottonwood-willow)
  vs. non-native (tamarisk) as neotropical migrant
  warbler foraging habitat.

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Projected Migration Paths of Neotropical Migrant
Birds
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Baja California Native
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Cibola Native
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Salt Cedar
Baja California
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Methods
Point counts
Mist netting
ForagingObservations
InvertebrateSampling
Tree Phenology
Vegetation sampling
AUWA
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Results
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MGWA
NAWA
BTYW
Relative Warbler Abundance
WIWA
OCWA
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Honey Mesquitehigh flower
Honey Mesquitelow flower
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Tamariskin flower
Baja California
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Warbler abundance and flower phenology on
Tamarisk and Honey Mesquite
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a
a,c
a,b,c
a,b,c
a,b,c
a,b,c
b
a,c
Plt0.001
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P0.077
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Invertebrate Sampling
Cibola Native
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Foliage Invertebrates on Riparian Tree Species
b
p lt.001
a,c
c
a,c
a
Non-Native Habitat
Native Habitat
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Discussion
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MGWA
NAWA
BTYW
Relative Warbler Abundance
WIWA
OCWA
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6m
NAWA
BTYW
AUWA
YWAR
LUWA
Relative foraging ht.
BTYW
OCWA
LUWA
NAWA
YWAR
NAWA
OCWA
WIWA
3m
WIWA
AUWA
Cibola NWR
Mesquite
Tamarisk
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Overall bird abundance as related to vegetation
composition
R20.52
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Neotropical migrant bird abundance as related to
vegetation composition
R20.57
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Conclusions

• Neotropical migrant warblers partition arrival
  times on the lower Colorado River.
• Neotropical migrant warblers partition foraging
  locations within vegetation strata.
• Foraging locations of neotropical migrant
  warblers differ between native and introduced
  vegetation.
• Insects are more abundant in native vs.
  introduced habitats along the lower Colorado
  River corridor.
• Neotropical migrant warblers prefer native over
  introduced vegetation along the lower Colorado
  River corridor, and respond differently to
  varying amounts of native vegetation.

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a
a,b
a,c
a
a
a
a
b,c
P lt 0.001