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The Wilson Journal of Ornithology 123(1):48—58, 2011 
SEASONAL FECUNDITY AND SOURCE-SINK STATUS OF 
SHRUB-NESTING BIRDS IN A SOUTHWESTERN RIPARIAN CORRIDOR 
L. ARRIANA BRAND 13 - 4 AND BARRY R. NOON 1 2 
ABSTRACT.—Saltcedar ( Tamarix spp.) has increasingly dominated riparian floodplains relative to native forests in the 
southwestern U.S., but little is known about its impacts on avian productivity or population status. We monitored 86 
Arizona Bell’s Vireo ( Vireo bellii arizonae ), 147 Abert’s Towhee ( Melozone aberti), and 154 Yellow-breasted Chat ( Icteria 
virens ) nests to assess reproductive parameters in cottonwood-willow ( Populus-Salix ), saltcedar, and mesquite ( Prosopis 
spp.) stands along the San Pedro River, Arizona during 1999-2001. We also assessed source-sink status for each species in 
each vegetation type using field data combined with data from the literature. There were no significant differences in 
reproductive parameters between vegetation types for Abert’s Towhee or Yellow-breasted Chat, although seasonal 
fecundity was quite low across vegetation types for the latter (0.75 ± 0.14; mean ± SE). Bell’s Vireo had extremely low 
seasonal fecundity in saltcedar (0.10 ± 0.09) and significantly fewer fledglings per nest in saltcedar (0.09 ± 0.09) 
compared with cottonwood (1.07 ± 0.32). Point estimates of X were substantially <1 for all three focal species in all 
habitats indicating the entire study area may be performing as a sink; 90% Cl of X included 1 only for Abert's Towhee 
across vegetation types and Bell’s Vireo in cottonwood vegetation. These results are surprising given the San Pedro is 
considered to be one of the best remaining occurrences of lowland native riparian vegetation in the southwestern United 
States. Received 15 April 2010. Accepted 8 October 2010. 
The proportion of lowland riparian corridors 
covered by exotic saltcedar (Tamarix spp.) 
relative to native broadleaf forests and shrublands 
has increased dramatically in the Southwest over 
the past 50 years (Hunter et al. 1987, Sher et al. 
2000, Morisette et al. 2006, Stromberg et al. 
2007). Avian density responses to these vegeta¬ 
tion types have been documented in numerous 
studies across river systems, yet few studies have 
assessed measures of productivity for southwest¬ 
ern riparian birds. In particular, little is known 
about the impacts of exotic vegetation on avian 
productivity or population status in the region 
(Sogge et al. 2008). 
Many canopy-nesting bird species have highest 
densities in tall, gallery cottonwood-willow ( Po¬ 
pulus-Salix) forests compared with saltcedar, 
although saltcedar has maintained high abundance 
of some shrub-nesting species (Hunter et al. 1987, 
1988; Ellis 1995; Brand et al. 2008, 2010). Exotic 
vegetation is one circumstance in which patterns 
of abundance and productivity may diverge (Van 
1 Department of Hydrology and Water Resources, 
University of Arizona, Sustainability of Semi-Arid Hydrol¬ 
ogy and Riparian Areas (SAHRA) Center, P. O. Box 
210158-B, Tucson, AZ 85721, USA. 
Department of Fish, Wildlife, and Conservation Biol¬ 
ogy, Colorado State University, Fort Collins, CO 80523 
USA. 
Current address: U.S. Geological Survey, Western 
Ecological Research Center, San Francisco Bay Estuary 
Field Station, 505 Azuar Drive, Vallejo, CA 94592, USA. 
Corresponding author; e-mail: arriana_brand@usgs.gov 
Home 1983, Battin 2004, Bock and Jones 2004); 
thus, it is important to assess productivity and 
population status for shrub-nesting birds in 
different habitat types comprised of native and 
exotic vegetation. Brand et al. (2010) documented 
nest survivorship of common shrub-nesting birds 
on the San Pedro River and found a tendency for 
Arizona Bell’s Vireo (Vireo bellii arizonae) to 
have higher nest survivorship in cottonwood 
versus mesquite (Prosopis spp.) and saltcedar. 
but no difference in nest survivorship between 
vegetation types for Yellow-breasted Chat (Icteria 
virens) and Abert’s Towhee (Melozone aberti). 
Nest survival is only one component of avian 
fecundity, and further work is needed to document 
productivity and population status for these 
species. Source-sink models have been applied 
extensively to assess habitat quality of fragmented 
versus contiguous habitats across the Midwest and 
other regions in the U.S. (e.g., Pulliam 1988, 
Donovan et al. 1995, Fauth 2000, Yackel Adams 
et al. 2007), but little is known about productivity 
or source-sink status of shrub-nesting birds in 
southwestern riparian habitats. 
Our primary research objectives were to assess 
repioductive parameters (e.g., clutch size, young 
per nest, seasonal fecundity) and source-sink 
status of three relatively common shrub-nesting 
bird species on the San Pedro River in southeast¬ 
ern Arizona among vegetation types. This study 
supplements and provides greater context for 
previous nest survivorship estimates (Brand et 
al. 2010) for this population with additional 
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