Acoustic Traits of Three Hawaiian Honeycreepers in a Fragmented Landscape

Habitat fragmentation is a global issue impacting animal populations and is primarily caused by human activities. The main consequences of habitat fragmentation are habitat loss and patchiness, although fragmentation can also increase habitat diversity and landscape complementation. While the impact of habitat fragmentation on animal communities is heterogeneous due to positive and negative effects on biodiversity, its influence on the diversity of learned cultural traits within those communities remains less understood. This study assesses the acoustic traits of three species of native Hawaiian honeycreepers ('Apapane <i>Himatione sanguinea</i>, 'I'iwi <i>Drepanis coccinea</i> and Hawai'i 'Amakihi <i>Chlorodrepanis virens</i>) across a naturally fragmented landscape. Using automatic recording units, we gathered bird vocalization data from five bird populations across the Big Island of Hawai'i and used these data to manually identify the distinct syllables vocalized by individuals of the three species. Additionally, we assessed the habitat connectivity between these five populations using a model that considered the land-cover type, the species' likelihood of occurrence in each land-cover, the cost of multiple dispersal pathways, and bird susceptibility to a disease constrained by topography. Finally, we compared the acoustic repertoires among the different populations and examined the relationship between their acoustic dissimilarity, geographic distance, and inter-population connectivity. The results show that the three honeycreeper species have large repertoires (i.e., with 52-215 different syllables), with low overlap among study sites. Acoustic dissimilarity was not related to geographic distance for any species, although inter-population connectivity determined the acoustic traits of one of the species ('I'iwi <i>Drepanis coccinea</i>). The study suggests that landscape connectivity plays a variable role in shaping acoustic differences. Overall, this study contributes to a better understanding of the impact of habitat fragmentation on the acoustic diversity of animal communities and highlights the importance of considering cultural traits in conservation efforts.