Context Anthropogenic noise is relatively new to natural soundscapes and may have adverse effects on acoustically active species. In birds, adverse effects include changes in vocalization patterns. Helicopters and songbirds are ubiquitous in protected natural areas but the effect of helicopter noise on songbirds has never been assessed. Objectives Our objective was to determine if helicopter noise affects temporal characteristics of songbird vocalizations within protected natural areas. Methods We collected soundscape recordings in three protected areas with varying levels of helicopter tour activity, including one with the second highest air tour activity in the United States. We examined songbird response to helicopter noise at the species level by measuring changes in vocalization time, and at the community level by employing the Bioacoustic Index, an acoustic measure of biological sound. Results We found a strong association between increasing helicopter noise and songbird vocalizations, indicating that some bird species use temporal shifts in vocalizations to mitigate masking effects from helicopter noise. The strength and direction of the response was species-specific, suggesting differences in resilience to helicopter noise between species. Furthermore, our results suggest that bird response to helicopter noise is strongest in areas with very loud and frequent helicopter traffic. Conclusions Our study is the first to examine and demonstrate impacts of helicopter noise on songbird vocalizations. Our results may serve as the foundation of an air tour management plan that considers reducing the number of helicopter overflights over protected natural areas and enforcing higher flight altitudes to decrease noise power levels.

中文翻译：

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夏威夷自然保护区与直升机噪音相关的鸣禽发声的时间变化

背景 人为噪声对于自然音景来说相对较新，可能对声学活跃的物种产生不利影响。在鸟类中，不利影响包括发声模式的变化。直升机和鸣禽在自然保护区无处不在，但直升机噪音对鸣禽的影响从未得到评估。目标 我们的目标是确定直升机噪音是否影响自然保护区内鸣禽发声的时间特征。方法 我们收集了三个保护区的音景录音，这些保护区具有不同程度的直升机旅游活动，其中一个在美国的空中旅游活动中排名第二。我们通过测量发声时间的变化，研究了鸣禽在物种层面对直升机噪音的反应，在社区层面，通过使用生物声学指数，一种生物声音的声学测量。结果我们发现增加的直升机噪音和鸣禽的叫声之间存在很强的关联，这表明一些鸟类使用发声的时间变化来减轻直升机噪声的掩蔽效应。反应的强度和方向是物种特异性的，表明物种之间对直升机噪音的恢复能力存在差异。此外，我们的结果表明，在直升机交通非常嘈杂和频繁的地区，鸟类对直升机噪音的反应最强。结论我们的研究是第一个检查和证明直升机噪音对鸣禽发声的影响的研究。