Helicopter noise in Hawaiʻi's protected natural areas changes temporal characteristics of songbird vocalizations

Abstract

Anthropogenic noise has adverse effects on birds, including decreased breeding success, increased flushing behavior, and changes in vocalization patterns. The avifauna in Hawaiʻi is among the most threatened in the world, and helicopter noise in Hawaiʻi’s forests could be another stressor native birds face in addition to disease, habitat loss, and non-native species, but its effect on bird vocalizations has never been assessed. My primary objective was to determine if helicopter noise affects the temporal characteristics of songbird vocalizations within protected natural areas. I placed automated acoustic recorders in three forested areas that are subjected to helicopter traffic from air tours, two in Hawaiʻi Volcanoes National Park and one in the Upper Waiākea Forest Reserve on the Island of Hawaiʻi. I found that songbirds change their vocalization time in response to the power (dB) of approaching helicopter noise. These results indicate that birds are using temporal shifts in vocalizations to mitigate masking effects from helicopter noise. Additionally, I found that the strength and direction of the response is species-specific. Warbling White-eye increased vocalization time, and ‘Apapane and Japanese Bush-warbler decreased vocalization time as helicopter noise power increased, suggesting differences in resilience to helicopter noise between species. Furthermore, results of this study suggest that birds respond the strongest to helicopter noise in areas with very loud and frequent helicopter traffic. My results demonstrate impacts of anthropogenic noise on native bird habitat and may serve as the foundation of an air tour management plan that considers reducing the number of helicopter overflights over protected natural areas to 4 or less helicopters per hour and enforcing a higher flight altitude to decrease power levels of overflights to 191 dB or less.