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This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Throughout the world, birds represent the primary type of wildlife that people experience on a daily basis. However, a growing body of evidence suggests that alterations to the acoustic environment can negatively affect birds as well as humans in a variety of ways, and altered acoustics from noise pollution has the potential to influence human interactions with wild birds. Birds respond to approaching humans in a manner analogous to approaching predators, but the context of the interaction can also greatly influence the distance at which a bird initiates flight or escape behavior (i.e., flight initiation distance or FID). Here, we hypothesized that reliance on different sensory modalities to balance foraging and threat detection can influence how birds respond to approaching threats in the presence of background noise. We surveyed 12 songbird species in California and Wyoming and categorized each species into one of three foraging guilds: ground foragers, canopy gleaners, and hawking flycatchers and predicted FIDs to decrease, remain the same and increase with noise exposure, respectively. Contrary to expectations, the canopy gleaning and flycatching guilds exhibited mixed responses, with some species exhibiting unchanged FIDs with noise while others exhibited increased FIDs with noise. However, FIDs of all ground foraging species and one canopy gleaner decreased with noise levels. Additionally, we found no evidence of phylogenetic structure among species' mean FID responses and only weak phylogenetic structure for the relationship between FIDs and noise levels. Although our results provide mixed support for foraging strategy as a predictor of bird response to noise, our finding that most of the species we surveyed have shorter FIDs with increases in noise levels suggest that human observers may be able to approach ground foraging species more closely under noisy conditions. From an ecological perspective, however, it remains unclear whether these mixed responses translate into lost foraging opportunity for hypervigilant birds that flee a threat too soon or greater predation risk due to impaired surveillance for those that only respond once approaching threats are near.

Protected natural areas are not free from noise, especially noise generated by traffic within park boundaries. Natural soundscapes are important for maintaining community structure, providing positive visitor experiences, and increasing visitor support for management actions that reduce impacts on natural resources. To test experimental quieting as a strategy to increase both wildlife habitat quality and visitor experience, we enforced decreased speed limits and presented educational signage to reduce sound levels along a road system in an alternating, on-off block design within Grand Teton National Park, Wyoming, USA. We continuously recorded background sound levels while conducting bird space use assessments and visitor-intercept surveys along the experimental corridor. Our mitigation approach lowered sound levels during sign-present weeks, yet there was no relationship between bird space use near roadways and traffic noise, perhaps due to the increased duration of noise exposure created by lower speed limits. There was, however, a relationship between visitor perception of birdsong diversity and background sound level. Critically, visitors preferred soundscape mitigation strategies limiting personal access in exchange for better experiences in natural soundscapes.

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A growing body of evidence suggests that traffic noise negatively affects wildlife. Protected natural areas are not free from noise exposure, both external to and within park boundaries. Natural soundscapes are important in many aspects of animal life histories, for increasing positive visitor experiences, and for providing psychological ecosystem services. To examine the use of signs as an effective traffic noise mitigation strategy, we experimentally altered speed limits from 45 mph to 25 mph, with additional educational signage, along the Oxbow Bend traffic corridor in Grand Teton National Park, USA. We continuously recorded sound levels between alternating week-long blocks while conducting avian point counts at each station. We detected 2,217 individuals of 48 species across all stations throughout the study. To assess visitor experiences with the soundscapes and visitor attitudes towards sign use and management strategies, we conducted stated-choice intercept surveys along a park turnout within the experimental corridor. We administered 471 surveys at an 82% response rate. Future data will evaluate impacts of traffic noise on avian abundance and distributions, visitor attitudes towards mitigation strategies, and the potential coupling between human and natural systems via the soundscape.   Featured photo from Figure 2 in report.