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The Wilson Journal of Ornithology 123(3):628—631, 2011 
First Record of Interspecific Breeding of Least Bell’s Vireo and 
White-eyed Vireo 
Melissa A. Blundell l 2 - 3 and Barbara E. Kus 1 * 
ABSTRACT.—We provide the first known docu¬ 
mentation of a male Least Bell's Vireo (Vireo bellii 
pusillus) breeding with a female White-eyed Vireo ( V. 
griseus) and the first report of a White-eyed Vireo 
breeding in California at the San Luis Key River. 
Oceanside. San Diego County. We discovered the pair 
building a nest on 12 May 2010. The female laid four 
eggs, and the pair successfully raised and fledged four 
nestlings. We collected DNA samples from each 
nestling and the female during the nestling stage and 
banded them with a numbered federal leg band for 
future identification. We obtained detailed'"nest mea¬ 
1 U.S. Geological Survey. Western Ecological Research 
Center. 4165 Spruanee Road. Suite 200. San Diego CA 
92101, USA. 
3 Current address: I Shields Avenue. Department of 
Evolution and Ecology. University of California, Davis CA 
95616, USA. 
Corresponding author; e-mail: mablundell@ucdavis.edu 
surements after fledging and monitored the territory for 
further nesting attempts. No additional nesting attempts 
were detected. Received 29 November 2010. Accepted 
29 March 2011. 
The Least Bell's Vireo (Vireo bellii pusillus) is 
a federally endangered migratory songbird that 
breeds from southern California. USA to northern 
Baja California, Mexico between late March and 
mid-August ( Kus et al. 2010) with the majority ol 
the population breeding in San Diego Count) 
along the San Luis Rey and Santa Margarita 
rivers. The White-eyed Vireo (V. griseus ) i s a 
migratory songbird that primarily breeds in 
eastern North America (from southern Florida to 
southeast Massachusetts and west through Illi¬ 
nois) and into central North America (from 
