The Wilson Journal of Ornithology 123 ( 3 ): 464 ^ 71 , 2011 
SONG DIFFERENCES AMONG SUBSPECIES OF YELLOW-EYED 
JUNCOS (JUNCO PHAEONOTUS) 
NATHAN D. PIEPLOW 1 - 4 AND CLINTON D. FRANCIS 2 - 3 
ABSTRACT.—We compared 13 song features among three populations of Yellow-eyed Junco (Junco phaeonotus): J. p. 
bairdi from Baja California Sur. Mexico; J. p. palliatus from southeast Arizona. USA; and J. p. phaeonotus from Oaxaca. 
Mexico. Songs of J. p. hairdi differed significantly from those of J. p. palliatus in II of 13 features and differed 
significantly from those of J. p. phaeonotus in six of 13 features. Songs of J. p. palliatus differed significantly from those of 
J. p. phaeonotus in only four of 13 features. Discriminant function analysis clearly distinguished songs of / p. hairdi from 
those of the two other subspecies, which were not clearly distinguishable from one another. Additional investigations using 
playback experiments and genetic analyses may be warranted to better evaluate the merits of promoting J. p. bairdi to 
species status. Received 22 August 2010. Accepted 24 January 2011. 
Ornithologists have long hypothesized that 
geographic song variation affects gene flow and 
can lead to assortative mating, reproductive 
isolation, and population divergence (Grant and 
Grant 19%. Irwin et ul. 2001, Slabbekoorn and 
Smith 2002). However, the relative extent to 
which geographic variation in bird song influenc¬ 
es speciation remains controversial (Baker and 
Cunningham 1985. Slabbekoorn and Smith 2002). 
There are now several recent examples of song 
variation functioning as a reproductively isolating 
barrier among co-occuring cryptic species (e.g., 
Irwin et al. 2001, Toews and Irwin 2008), 
suggesting song variation may also act as a 
barrier to hybridization among populations that 
are currently separated, were they to become 
sympatric in the future. 
The 'Yellow-eyed Junco ( Junco phaeonotus) is 
a sedentary resident of arid conifer and pine 
(Pinus)- oak ( Quercus) forests with a current 
distribution restricted to mountains between 
southeastern Arizona. USA and Guatemala (Sul¬ 
livan 1999). Geographic song variation in the 
Yellow-eyed Junco is obvious to the ear and is 
one factor contributing to disagreement about how 
many species are involved in the complex. The 
fifth edition ot the American Ornithologists’ 
Union Checklist (AOU 1957) recognized two 
species; Baird’s Junco (currently J. p. hairdi ), 
isolated in the mountains of Baja California Sur 
Mexico; and Yellow-eyed Junco (J. p. palliatus 
M745-B White Rock Circle. Boulder. CO 80301. USA 
Ecology and Evolutionary Biology. UCB 334. Univer¬ 
sity of Colorado, Boulder, C'O 80309, LISA 
^ Sl,ilc A20 °- 
4 Corresponding anchor; e-rn.il: „piep|„ w @ gIIlaiUom 
and J. p. phaeonotus), occurring in mainland 
Mexico and Arizona, USA. The AOU (1957) did 
not mention ./. p. fulvescens or J. p. alticola. 
which occur in the mountains of Chiapas, Mexico 
and Guatemala, respectively. The 32 nd AOU 
checklist supplement (AOU 1973) lumped Baird’s 
Junco into Yellow-eyed Junco (J. phaeonotus. 
including J. p. fulvescens and J. p. alticola) 
without explaining the rationale for the change, 
although it cited authors who had lumped the 
groups (Paynter 1970) or recommended doing so 
(Mayr 1942). The AOU continues to treat all 
juncos with yellow eyes as a single species (AOU 
1998). Howell and Webb (1995), however, 
recognized J. p. hairdi as a separate species from 
the rest of die Yellow-eyed Junco complex. 
Howell and Webb (1995) describe marked 
differences in song between J. p. hairdi and 
mainland birds: J. p. phaeonotus sings “a varied 
series ol bright chips, often with trills or buzzes 
thrown in. typically the last note rising or 
upslurred... |that) can be confused with songs of 
Rufous-sided Towhee [Pipilo spp.] and Bewick's 
Wren [Thryonumes bewickiiy ’ (page 731). while 
J. p. hairdi sings "a pleasant, tinkling, and trilled 
warble... (that] may suggest a small Troglodytes 
wren and strikingly different from mainland 
Yellow-eyed Juncos" (page 730). 
Differences between the songs of mainland J. p- 
phaeonotus and peninsular J. p. bairdi may be 
obvious to the human ear, and contributed to 
Howell and Webb’s (1995) treatment of the 
populations as separate species, but the distinction 
has not been investigated quantitatively. The 
objective of this study was to investigate the 
extent and nature of vocal differences between 
J- p. bairdi Yellow-eyed Juncos and mainland 
Yellow-eyed Juncos from two regions (Arizona, 
464 
