Documenting acoustic variability among windward Hawai'i 'Amakihi (Hemignathus virens virens) populations on Hawai'i Island

Abstract

Vocalizations play a fundamental role in many aspects of a bird's life, including territoriality, mate choice, individual recognition, and predator avoidance. This is the first study to investigate how vocalizations differ across populations of a Hawaiian honeycreeper. I recorded song from 329 adult male Hawaii 'Amakihi (Hemignathus virens virens) in five populations across an elevational gradient on the windward side of Hawaii Island during the 2011-2013 breeding season and used sound analysis software to examine how eight song components vary within and among populations. Our results demonstrated that song varies greatly among populations with greatest divergence and lowest song variability in the low elevation population, where 'Amakihi have recently recovered from a disease-induced bottleneck. I also tested predictions of the Acoustic Adaptation Hypothesis (AAH) by examining how song characteristics vary between open and closed understory vegetation. 'Amakihi in open understory sang at higher frequencies relative to neighboring 'Amakihi in dense understory, thus providing moderate support for the AAH. This study demonstrates that both isolation and habitat heterogeneity has led to localized structuring of song over relatively short geographic distances.