Antiphonal duetting and sex hormones in the tropical bush shrike Laniarius funebris (HARTLAUB)

Abstract

We investigated changes in antiphonal duetting with phases of reproduction and circulating levels of luteinizing hormone, testosterone, and estradiol in slate-colored boubous ( Laniarius funebris) breeding in aviaries. Frequency of overall male singing did not vary with reproductive phase while frequencies of female singing and female vocal responses to male song were reduced during incubation and feeding of nestlings. This resulted in significant changes in frequency of duetting. Males sang the sexual song type M1 more often during courtship and nest building than during the nestlings phase. Their territorial song types M2 and M4 did not vary with breeding phase. Females were less responsive to M1 during incubation and to M2 during the nest building and nestlings than during the courtship phase. Plasma levels of luteinizing hormone and testosterone increased in males from the prebreeding to the courtship phase. While testosterone decreased already during nest building and remained low during subsequent phases of reproduction, luteinizing hormone decreased during incubation and feeding of nestlings. Female luteinizing hormone levels were highest during nest building. Female estradiol levels decreased from nest building to incubation and increased again during subsequent nest building. Female testosterone levels were low but not basal and did not vary with phase. Neither the overall male and female singing frequencies nor the frequencies of male song types were correlated with hormonal state. However, female participation in territorial duets M4 correlated positively with their testosterone levels. It is suggested that in this monogamous, duetting species with prolonged pairbonds behavioral cues between the mates are more important than the hormonal state in control of male and female singing.