Acoustic differentiation in a sub-oscine calls: females call with more entropy than males

Abstract

We quantified variation at the individual, pair and sex levels in acoustic attributes of Vermilion Flycatcher (Pyrocephalus rubinus)’s peent calls. We recorded calls of 15 pairs during the breeding season, and analyzed seven acoustic measures encompassing temporal, frequency and entropy measures. We run Principal Component Analysis to reduce the number of acoustic parameters; the first three principal components (PCs: PC1, PC2, and PC3) were related to call frequency, call entropy and call duration, respectively. These PCs were further used in Discriminant Function Analysis (DFA), and logistic regressions. Although all three PCs varied more among than within individuals, the DFA correctly classified only 57% of males and 63% of females, casting doubts on the possibility that the peent functions as an individual marker. At the pair level, only PC1 (call frequency) differed among pairs; however, the DFA correctly classified only 6.7%. of pairs. At the sex level, male peents had lower values of PC2 (call entropy) than female peents; the DFA correctly classified 66.7% and 73.3% of individuals as males and females, respectively (mean correct classification 70%). Binary logistic regression confirmed that only call entropy differed between sexes, and correctly classified 73.3% of females and 80% of males. Our data show sexual acoustic dimorphism in the peent, and open the possibility that variation in peent entropy may allow for sex discrimination in this species.