| Summary: | 碩士 === 臺灣大學 === 森林環境暨資源學研究所 === 95 === Duets are formed when pair members coordinate their songs with temporal precision. More and more evidence showed that these apparently cooperative displays could also be driven by sexual conflict. I combined a descriptive study and an experimental study to investigate the functions of duetting in Steere’s Liocichla. Experiments were carried out at Meifeng, central Taiwan during breeding season from 2005 to 2006. In the descriptive study, detailed quantification of duet structure and duetting behavior is provided to understand the vocal strategies of both sexes. I recorded vocalizations under natural condition from 15 breeding pairs. Females rarely sang spontaneously, and almost all duets were led by males (96.43%). Male Steer’s Liocichlas sang whistle songs and 9.71% of which were followed by females with buzz notes to form duets. Female notes extend a narrower frequency range, but modulate more rapidly than male notes. Songs of both sexes are highly individualistic; nevertheless, male songs contain higher individuality than female songs. Each male have a repertoire of 2-4 types, but all female songs are of the same type. While male song rate decreased once offspring hatched, female responsiveness remained equally low irrespective of breeding status. Males sang shorter song bouts if their mates were more willing to join in and joined more quickly. In the experimental study, I performed stereo duet playbacks to ten pairs to test hypotheses of functions of duetting. Treatments included playback of female solo, male solo, pair duet of strangers and pair duet of neighbors. Treatments were played through opposite channels in two rounds. In the first round, male song initiation rates were not significantly different among the three stranger treatments but lower in neighbor duet playback. In the second round, males initiated fewer songs in the female solo and neighbor duet playback. In both rounds, females answered their partner’s song more frequently in response to female solo and stranger duet playbacks. In most cases (10/14), members of a pair approached speakers together. In cases which pair members approached different speakers, birds spent the majority of time on the side of the speaker broadcasting elements of the same sex with them. Taken together, the descriptive study and experimental study showed consistent results. Male and female Steere’s Liocichlas have pronounced differences in vocal structure and duetting strategies. Responses to simulated intrusions indicate that in addition to joint territory defense, duetting in this species may also serve a mate guarding function. Sexual differences in vocal structure comprising duets and the way how duets are delivered suggest that under the apparently cooperative act, sexual conflict may operate in the evolution of duetting in Steere’s Liocichla.
|
|---|
