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

  • Alejandro Ariel Ríos-ChelénEmail author
  • Xhareni Díaz-Lezama
  • Bibiana Montoya
Original Article


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.


Vermilion flycatcher Pyrocephalus rubinus Suboscine Call Sexual dimorphism Animal communication 


Akustische Differenzierung bei suboszinen Rufen: Weibchen rufen mit mehr Entropie als Männchen. Wir quantifizierten die Variation akustischer Eigenschaften des sogenannten Peent-Rufes (ein spitzer und langer Ruf, engl. peent call) beim Rubintyrann (Pyrocephalus rubinus) auf individueller, paarbezogener und geschlechtsspezifischer Ebene. Dafür nahmen wir Rufe von 15 Paaren während der Brutsaison auf und analysierten sieben akustische Parameter, die Zeit-, Frequenz- und Entropiemessungen umfassten. Wir führten Hauptkomponentenanalysen durch, um die Anzahl an akustischen Parametern zu reduzieren. Die ersten drei Hauptkomponenten (engl. principal components, PCs: PC1, PC2 und PC3) standen im Zusammenhang mit Ruffrequenz, -entropie bzw. -dauer. Diese PCs wurden weiter für Diskriminanzanalysen (engl. Discriminant Function Analysis; DFA) und logistische Regressionen verwendet. Auch wenn alle drei PCs größere Variationen zwischen den Individuen als innerhalb der Individuen zeigten, klassifizierte die DFA nur 57% der Männchen und 63% der Weibchen korrekt. Dies lässt Zweifel an der Funktion des Peent-Rufes als individuelles Kennzeichen aufkommen. Auf paarbezogener Ebene zeigte nur PC1 (Ruffrequenz) Unterschiede zwischen den Arten. Jedoch klassifizierte die DFA nur 6.7% der Paare korrekt. Auf geschlechtsspezifischer Ebene zeigten männliche Peent-Rufe geringere Werte bei der PC2 (Rufentropie) als weibliche Peent-Rufe. Die DFA klassifizierte 66.7% bzw. 73.3% der Individuen korrekt als Männchen bzw. Weibchen (durchschnittlich richtige Klassifizierung 70%). Die binäre logistische Regression bestätigte, dass sich nur die Rufentropie zwischen den Geschlechtern unterschied und klassifizierte 73.3% der Weibchen und 80% der Männchen korrekt. Unsere Daten weisen auf einen akustischen Sexualdimorphismus beim Peent-Ruf hin und eröffnen die Möglichkeit, die Variation in der Peent-Entropie zur Geschlechtsunterscheidung in dieser Vogelart zu nutzen.



We thank Margarita Martínez-Gómez for logistic support. We are grateful to Laura Corkovic who translated the title and abstract from English to German. We are thankful to two reviewers who improved the quality of this paper. This study complies with the current laws of the country in which they were performed.

Compliance with ethical standards

Conflict of interest

The authors declare that they have no conflict of interest.

Supplementary material

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© Deutsche Ornithologen-Gesellschaft e.V. 2020

Authors and Affiliations

  1. 1.Centro Tlaxcala de Biología de la ConductaUniversidad Autónoma de TlaxcalaTlaxcalaMexico
  2. 2.Escuela de BiologíaBenemérita Universidad Autónoma de PueblaPueblaMexico

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