Janes and Ryker • BLACK-THROATED GRAY WARBLER SONG 
345 
TABLE 2. Geographic extent of the Type I song forms 
of Black-lhroated Gray Warblers in southwestern Oregon 
and northern California. Numbers in parentheses indicate 
song variant areas whose complete distributions are 
undescribed. 
Song variant 
Area (km 2 ) 
Emigrant 
2 
Applegate 
472 
Caves 
1,631 
Crooks 
209 
Grave 
503 
Diamond Rock 
107 
Cow 
91 
Starvout 
170 
Days 
(333) 
Humbug 
(825) 
Happy Camp 
(165) 
Agness 
(415) 
Winchuck 
(1,050) 
Smith 
(125) 
as it neared the Caves population to the southwest. 
A distinct tonal note in the A-phrase syllables and 
a tendency for B 3 and B 4 to fuse distinguished this 
song. 
Geographic Extent.— The geographic extent of 
variants differed (Table 2). The largest exceeded 
1.500 knr within the study area, and limited 
sampling beyond the study area indicates the Days 
variant exceeded 3,000 km 2 . Five of the variants 
occupied <5% of the area of the largest. 
All variants occupied a fragmented range 
resulting primarily from natural habitat heteroge- 
ne >ty but also due to human activities (e.g., 
agriculture, housing, and forest management 
activities). Groups of males sharing territorial 
boundaries and surrounded by uninhabited areas 
seldom exceeded 12-20 singing males, and many 
included only one to three males. 
DISCUSSION 
Type I songs of Black-throated Gray Warblers 
exhibit considerable geographic variation. Several 
variants were structurally distinct and occupied 
discrete areas, but others were not. either 
overlapping other variants geographically or 
possessing intermediate features between adjacent 
variants. The most fragmented song populations 
bad high variation even among males within local 
Populations. Some dialects can be identified, but 
Type I songs of Black-throated Gray Warblers do 
n °l exhibit a clear system of dialects in the 
manner noted among Hermit Warblers (Janes and 
Ryker 2006) and White-crowned Sparrows (Not- 
tebohm 1969, Chilton and Lein 1996), 
The high geographic overlap and variability 
within the region noted in some Type 1 variants of 
Black-throated Gray Warblers suggests a dynamic 
system. New variants appear to arise and spread 
by gradual infiltration into other song variant 
areas while other variants decline fracturing into 
small disjunct song populations, eventually being 
overwhelmed by more vigorous variants. 
Sampling over a 16-ycar period, representing 
only five of the song forms reported indicated 
there was no change in variant boundaries or 
change in song structure (SWJ and LR, unpubl. 
data). This evidence suggests that, while this is 
likely a dynamic system, changes occur over a 
period of many decades or longer. 
The Type I dialects of Hermit Warblers in 
comparison are more distinct in both structure and 
geographic distribution (Janes and Ryker 2006). 
suggesting a long history of independent devel¬ 
opment. Variation is apparent within dialect areas, 
but songs with intermediate characteristics be¬ 
tween adjacent dialects were rare. Temporal 
changes in the distribution and structure of 
dialects appear to occur in a different manner 
than suggested for Black-throated Gray Warblers. 
One temporal change has been noted in dialect 
boundaries of Hermit Warbler dialects in southern 
Oregon. This involved the advance of one dialect 
boundary by 6 km and the complementary retreat 
of the neighboring dialect (SWJ and LR, unpubl. 
data). A similar system of moving boundaries was 
described for dialects of White-crowned Sparrows 
(Chilton and Lein 1996). 
The diversity of variants in the region is 
comparable between Black-throated Gray and 
Hermit warblers. Nine of the variants of Black- 
throated Gray Warblers reported occurred in the 
area where eight dialects of Hermit Warblers song 
were previously identified (Janes and Ryker 
2006). However. Hermit Warblers occupy a much 
ereater portion of the area and exhibit a more 
continuous distribution. The area occupied by 
most Black-throated Gray Warbler variants is 
much smaller due to more limited suitable habitat. 
The most restricted Hermit Warbler dialect 
encompassed 688 knr. In contrast, five of the 
eight variants of Black-throated Gray Warblers 
for which distributions were completely described 
occurred in areas <250 km 2 . 
The considerable variation in Type I song in 
these two western wood-warblers is in contrast to 
