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THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 123, No. 3. September 2011 
of a single trill (a single syllable rapidly repeated), 
while songs of the 'Red-backed' form in northern 
Arizona (J. hyentalis dorsalis) frequently consist 
of two or three trills, or a trill with one or two 
buzzy notes (Thatcher 1968. Sibley 2000, Chris¬ 
tian Nunes recordings), and are apparently inter¬ 
mediate in complexity between the songs of other 
Dark-eyed Juncos and those of J. p. palliatus 
Yellow-eyed Juncos in southeastern Arizona. This 
trend of increasing complexity may continue south 
at least to Oaxaca. It is presently unknown 
whether songs of the Yellow-eyed Junco subspe¬ 
cies south of the Isthmus of Tehuantepec (J. p. 
fulvescens and ./. p. alticola) differ from those 
north of the Isthmus, and wc do not know of any 
recordings of these taxa. Howell and Webb (1995: 
731) describe the song of J. p. alticola, which 
resides south of the isthmus, as “a varied series of 
bright chips, usually the last note rising... much 
like phaeonotus." Additional recordings from the 
two southernmost subspecies are needed to 
understand vocal variation among juncos. 
It is clear the song of J. p. bairdi is distinct 
from that of other Yellow-eyed Junco subspecies, 
but whether this difference is indicative of an 
important reproductive barrier is unknown. Still 
needed are field and molecular studies. Playback 
experiments are necessary to ascertain whether 
and how individuals of J. p. bairdi respond to 
songs from other regions and vice versa. Molec¬ 
ular analyses comparing mitochondrial and nu¬ 
clear DNA of J. p. bairdi with those groups 
included in Mila et al. (2007) may provide insight 
on whether gene How exists between Baja 
California juncos and populations on the mainland 
and, if it does not, how long the population has 
been genetically isolated and how it is related to 
the rest of the clade. Promotion to species status 
may be warranted if field and molecular studies 
confirm that J. p. bairdi is behaviorally and 
genetically distinct from mainland juncos. 
ACKNOWLEDGMENTS 
We thank Carat Beard more, David Kmeper, Richard 
Erickson. Gary Nunn. Eduardo Palacios, Victor Anguiano. 
Western Field Ornithologists, and the Sonoran Joint 
Venture for organizing and assisting with the expedition 
to the Sierra La Laguna, We thank the Cornell Laboratory 
of Ornithology. Borror Laboratory of Bioacoustics. Xeno- 
Canto, Tom Webber of the Florida Museum of Natural 
History. S. N. G. Howell. Christian Nunes, Andrew 
Spencer, and Richard Webster for help in obtaining 
additional recordings for analysis. We also thank Alexander 
Cruz and Sarah Wagner for helpful comments on an early 
version of this manuscript. CDF thanks the National 
Evolutionary Synthesis Center (NESCent) for support 
(NSF EF-0905606) during the final preparation of this 
manuscript. 
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