Isler and Whitney • SPECIES LIMITS IN AN ANTBIRD COMPLEX 
11 
plumage characters, such as the presence/absence 
of a black throat patch, served to distinguish 
almost all subspecies at the 100% level. The 
single exception was duidae and lepidonotus , 
whose differences in coloration (redder female, 
paler male in duidae ) may or may not prove to be 
clinal when additional specimens are obtained in 
Colombia. The clear differences in plumage 
characters led us to concentrate our analysis on 
the biogeographic relationships between members 
of pairs of parapatric populations. Considering 
duidae and lepidonotus as a single taxon (lepido¬ 
notus has priority), locality data indicated that 
geographic ranges of five pairs of taxa (poecili- 
notus/lepidonotiis , lepidonotus/griseiventris, gut- 
turalis/griseiventris, griseiventris/nigrigula , and 
nigrigula/vidua) were not separated, or only 
partially separated, by wide river barriers. Large 
geographic gaps in our knowledge of the taxa 
occupying these potential contact zones currently 
prevents us from ascertaining whether: (1) some 
or all of these plumage-defined populations are 
evolving independently and deserve species status 
under the BSC; (2) there is widespread intergra¬ 
dation between neighbors; or (3) secondary 
contact of populations is only incipient, and the 
evolutionary dynamic in regions of overlap is yet 
to unfold. Consequently, we reserve judgment on 
the possible species status of the taxa listed as 
subspecies. Field work in potential contact zones 
is needed not only to obtain morphological data 
and material for genetic analysis, but also to 
record vocalizations. Differences in vocal charac¬ 
ters between these populations did not meet our 
conservative requirements to be diagnosable, but 
recordings from contact zones may provide a 
different perspective. Geographically fine-grained 
recording of loudsongs can provide a test of 
whether vocalizations converge or diverge in 
contact zones, and it is possible that calls rarely 
recorded for the complex may differ diagnosably. 
Collections of specimens and vocal recordings 
are needed from the Andean foothills (>800 m) 
population of lepidonotus given the suggestion in 
vocalizations and preliminary molecular studies 
that it may be distinct from lowland populations. 
The two available examples of the contact call of 
lepidonotus >800 m were short in duration and 
therefore similar to that of griseiventris. 
Genetic analysis now underway at FMNH (J. 
M. Bates, pers. comm.) should provide relevant 
insights into the phylogenetic relationships of 
these taxa including whether members of para¬ 
patric pairs are closest relatives. Early results 
showed 6.8% divergence in two mitochondrial 
genes between nigrigula and griseiventris across 
the Rio Teles Pires near the confluence of the 
Rio Cristalino; 0.6% divergence of griseiventris 
between left bank Teles Pires and right bank Rio 
Jiparana; 0.5% divergence between nigrigula on 
right bank Teles Pires and two sites (Serra dos 
Carajas and 52 km S Altamira) of vidua (Bates et 
al. 2004). In addition, a study of speciation in the 
region of the upper Rio Negro in northwestern 
Brazil found 10.8% genetic divergence between 
poecilinotus and duidae (Naka 2010). Differences 
in duration of contact call notes of Willisornis 
populations north and south of the Amazon 
suggest an early divergence that should be 
relevant to evolutionary studies as well as 
systematics. 
Current knowledge provides only the “tip of 
the iceberg,” and valuable insights relevant to 
systematics, conservation, and broader studies of 
evolution await further investigation of the Will- 
isomis complex. 
ACKNOWLEDGMENTS 
We are deeply grateful to P. R. Isler for preparing the 
figures of spectrograms and for helpful comments, to J. V. 
Remsen Jr. for his careful review of an earlier version of the 
manuscript, and to L. F. Silveira and Fabio Schunck of 
MZUSP for excellent fieldwork and collection of speci¬ 
mens. Two anonymous reviewers and C. E. Braun provided 
helpful comments. L. M. Martinez supplied distributional 
data from COP. G. F. Budney and M. D. Medler provided 
recordings and distributional data from the Macaulay 
Library. We appreciate the efforts of Paul Sweet and 
Thomas Trombone in providing a large series of detailed 
photographs of specimens collected on Mt. Duida, Vene¬ 
zuela, housed in the AMNH. L. N. Naka contributed 
important location data and molecular results from northern 
Brazil. J. M. Bates provided descriptions of FMNH 
specimens and shared early results of his ongoing molecular 
study. G. A. Bravo confirmed the identification of 
specimens housed in the Instituto de Investigation de 
Recursos Biologicos Alexander von Humboldt. Finally, we 
thank the recordists credited in the Appendix, especially K. 
J. Zimmer, for providing recordings essential to this study. 
LITERATURE CITED 
Agne, C. E. Q. and J. F. Pacheco. 2007. A homonymy in 
Thamnophilidae: Dichropogon Chubb. Revista Brasi- 
leira de Omitologia 15:484-485. 
Baptista, L. F. and D. E. Kroodsma. 2001. Avian 
bioacoustics. Pages 11-52 in Handbook of the birds of 
the world. Volume 6. Mousebirds to hombills (J. del 
Hoyo, A. Elliott, and J. Sargatal, Editors). Lynx 
Edicions, Barcelona, Spain. 
