SHORT COMMUNICATIONS 
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FIG. 1. A male Least Bell’s Vireo (left) building a nest with a female White-eyed Vireo (right) at the San Luis Rey 
River, Oceanside. San Diego County. California (2010). Photograph by Lisa D. Allen. 
eastern Iowa to west-central Texas and northeast¬ 
ern Mexico) between early April and early August 
IHopp et al. 1995). White-eyed Vireos arc rare 
^grants in California, with 67 confirmed sight¬ 
ings statewide between 1969 and 2009. only eight 
of which occurred in San Diego County (Califor¬ 
nia Bird Records Committee 2007. 2010). Five of 
'he San Diego County sightings were during the 
breeding season, while three were fall migrants 
(| 1 Sep-30 Oct). We report the first known 
documentation of a Least Bell’s Vireo, one of four 
subspecies of Bell's Vireo ( V. bellii ), breeding 
W| Ih a White-eyed Vireo. This is the first 
documented case ol' a White-eyed Vireo breeding 
in California and appears to be the first successful 
nesting of a mixed pair of any two vireo species 
observed in the field. 
OBSERVATIONS 
We observed a male Least Bell’s Vireo 
breeding with a female White-eyed Vireo at the 
s an Luis Rey River. Oceanside. San Diego 
County, California (33 13.86' N. 117 20 . 68 ' 
W). One observer (MAB) observed a male Least 
Be ll's Vireo building a nest with a female White¬ 
eyed Vireo on 12 May 2010 (Fig. 1). The pair 
likely had just, started building the nest, as it was 
-10% complete and consisted of a woven 
hammock attached to the branch of an arroyo 
willow (Salix lasiolepis). The following day (13 
May), the nest was 60-70% complete with a 
strong cup formation. The Least Bell’s Vireo was 
identified as male as he sang on the nest. Two 
additional observers corroborated identification of 
the female as a White-eyed Vireo on the same 
day. Six days later (19 May) and 12 days later (25 
May), two and four eggs, respectively, were 
observed in the nest. The presence of eggs 
corroborated the White-eyed Vireo was female. 
The male was incubating the eggs during these 
two visits. The nest was still active on I June with 
four eggs and the female was incubating the 
clutch. Four days later (5 Jun), four nestlings 
ranging from 1 to 2 days of age were present, 
placing 3 June as the approximate hatch date. 
We banded the four nestlings (5-6.5 days of 
age) on 9 June with single anodized aluminum 
dark blue numbered federal bands. We used a mist 
net during the same visit to catch the female 
White-eyed Vireo as she approached the nest. We 
