Variability in the Repertoires and Singing Behavior of Male and Female ‘I‘iwi (Drepanis coccinea)

Abstract

Oscine passerines (songbirds) are notable for their complex, learned songs and an immense variability of vocal characteristics across the clade. Studying oscine vocal behavior can teach us about the selection forces that drive songbird evolution, but more research is needed on many species, especially with regard to female singing in tropical, monomorphic species. In this study, I cataloged and described the vocalizations and vocal behaviors of ‘i‘iwi (Drepanis coccinea), a Hawaiian honeycreeper, and compared male and female repertoire size, repertoire content, and vocalization rate. I recorded the vocalizations and behavior of individual ‘i‘iwi at Hakalau Forest National Wildlife Refuge, then examined spectrograms of ‘i‘iwi vocalizations, classified syllable types, and recorded quantitative measurements of time and frequency for each syllable. I selected seven male and six female ‘i‘iwi for statistical analysis. I observed whisper song, duetting, female solo singing, and females vocalizing from the nest among other behaviors, and was able to characterize a few common modes of ‘i‘iwi vocal behavior. I found no significant difference between male and female ‘i‘iwi in repertoire size, rate of vocalization, or proportion of shared syllables. A network analysis for modularity found that ‘i‘iwi repertoires are significantly modular, but modules mostly comprised single individuals rather than grouping ‘i‘iwi by sex. Additional measurements showed that ‘i‘iwi repertoires were highly individualistic. Overall, this study reveals previously unknown details about ‘i‘iwi vocal behavior and provides a baseline of knowledge that will contribute to ‘i‘iwi population monitoring tools and provide insight into the evolution of behavioral traits in ‘i‘iwi, among Hawaiian forest birds, and among songbirds worldwide.