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THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 123, No. 1, March 2011 
2000) levels (U.S. Department of Commerce 
2010). Our estimates likely represent drought 
conditions that have continued to be representa¬ 
tive and may endure with projected climatic 
conditions (Dixon et al. 2009). 
We are not aware of other source-sink or 
population status results from the region to 
compare for these species. Yellow-breasted Chat 
and Abert’s Towhee had stable trends in Arizona 
over the last 10- and 40-year periods based on 
Breeding Bird Survey (BBS) data (Sauer et al. 
2007). However, BBS population trends for these 
species were highly variable in Arizona over the 
period of the study (Sauer et al. 2007), which may 
indicate variability in population status among 
riparian systems. Further documentation of pop¬ 
ulation status, habitat selection, and habitat 
quality among watersheds over a similar time 
period is needed to gain landscape and regional 
perspectives of population dynamics for these 
species. Bell’s Vireos in Arizona, also based on 
Breeding Bird Survey (BBS) trends, had a non¬ 
significant decline over the past 40-years (-2.3% 
per year, P = 0.38) but declined significantly over 
the past 10-years ( — 3.7% per year, P = 0.0001; 
Sauer et al. 2007). The low nest survival rates on 
the Bill Williams River (Averill-Murray et al. 
1999) and low seasonal fecundity and X estimates 
in this study for the San Pedro are surprising since 
these rivers should represent some of the best 
habitat within the limited range of Arizona Bell’s 
Vireos (Kus et al. 2010). There is increasing 
evidence that additional conservation focus is 
needed for Bell’s Vireos in Arizona. The status of 
these species depends on their fecundity and 
survivorship, and we believe the future research 
effort needed to obtain this information from local 
populations is warranted. 
ACKNOWLEDGMENTS 
We appreciate the work of the field crew that assisted 
with data collection on the San Pedro River: Mark Faherty, 
Janine McCabe, Brian Acord, Carey Hill, Devin Biggs, 
Chris Putnam, Brynne Langan, and Dolly Crawford. The 
Bureau of Land Management, San Pedro Project Office, 
provided access to the San Pedro National Conservation 
Area as well as housing for the three summers of data 
collection effort. We are also grateful for permission to 
work on lands granted by numerous private landowners. We 
thank Steve Beissinger for discussions that contributed to 
this research. We also thank Julie Stromberg, James 
Diffendorfer, Clait Braun, and two anonymous reviewers 
for their helpful comments on this manuscript. Karl 
Benedict kindly provided the map of the study area. Data 
collection for this research was funded by the Strategic 
Environment Research and Development (SERDP) project 
CS-1100. Analysis and writing portions for LAB were 
supported by SAHRA (Sustainability of Semi-Arid Hydrol¬ 
ogy and Riparian Areas) under the STC Program of the 
National Science Foundation, Agreement #EAR-9876800. 
and the U.S. Environmental Protection Agency “Integrated 
Modeling and Ecological Valuation” EPA STAR GRANT 
Program #2003-STAR-G2. 
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