Isler and Whitney • SPECIES LIMITS IN AN ANTBIRD COMPLEX 
5 
FIG. 2. Loudsongs of Willisornis populations. Nomenclature follows recommendations of this paper. Acronyms for 
recording archives in Appendix. (A) W. p. lepidonotus, Kapawi Lodge, Pastaza, Ecuador (ISL BMW 157:001). (B) W. v. 
nigrigula , km 209 on BR 230 south of Itaituba, Para, Brazil (ISL BMW 226:002). (C) W. p. lepidonotus , Kapawi Lodge, 
Pastaza, Ecuador (ISL BMW 157:001). (D) W. v. vidua, Caxiuana, Para, Brazil (ISL BMW 109:022). Magnified notes are 
expanded 3X on frequency axis, 4X on time axis. 
differences in quality were apparent in the field 
and laboratory to the human ear. 
Differences in loudsong characteristics among 
other populations did not meet our criteria as 
diagnostic, but when values were plotted geo¬ 
graphically, distributional patterns emerged that 
may prove relevant to future species-level anal¬ 
ysis. For example, frequency measures of the first 
note of poecilinotus loudsongs (37 individuals) 
were higher pitched than those of duidae (18 
individuals), and ranges barely overlapped. When 
these frequency characters were mapped geo¬ 
graphically, the extreme examples of each popu¬ 
lation occurred at considerable geographic dis¬ 
tance from the contact zone, and loudsongs 
recorded closest to the contact zone (although 
only 2 individuals of each taxon) differed 
substantially. 
Similar differences were found between duidae 
and lepidonotus loudsongs with duidae notes 
delivered at lower frequencies and a slower pace. 
For example, the mean of the lowest frequency of 
the central note of duidae was 1,948 Hz (range = 
1,332-2,177, SD = 242, n = 18), whereas that of 
lepidonotus was 2,302 Hz (range = 2,177-2,678, 
SD = 128, n = 24), but the difference did not 
meet our significance test. Plotting frequency and 
pace geographically did not suggest a tendency 
for duidae loudsongs either to diverge or converge 
clinally with lepidonotus , although recordings are 
needed from the region where these populations 
are likely to come into contact. No significant 
