Individual differences show that only some bats can cope with noise-induced masking and distraction

Airport noise disturbs foraging behavior of Japanese pipistrelle bats

The expansion of anthropogenic noise poses an emerging threat to the survival and reproductive success of various organisms. Previous investigations have focused on the detrimental effects of anthropogenic noise on the foraging behavior in some terrestrial and aquatic animals. Nevertheless, the role of airport noise in impairing foraging activities of most wild animals has been neglected. Here, we aimed to assess whether foraging behavior in free-living Japanese pipistrelle bats (Pipistrellus abramus) can be disturbed by airport noise. We used audio recording to monitor foraging activities of bats at 11 sites around the runway of a municipal airport. We quantified noise level and spectra, aircraft activity, habitat type, nightly temperature, wind speed, and moon phase for each site. The analysis revealed that noise level and aircraft activity were significant negative predictors for the number of bat passes and feeding buzzes around the runway, even after controlling for the effects of other environmental factors. There was no marked spectral overlap between bat echolocation pulses and airport noise in the presence and absence of low-flying aircraft. The spectro-temporal parameters of echolocation vocalizations emitted by bats were dependent on noise level, aircraft activity, and habitat type. These results provide correlative evidence that airport noise can reduce foraging activities of wild pipistrelle bats. Our findings add to the current knowledge of adverse impacts of airport noise on foraging bats in artificial ecosystems and provide a basis for further research on the mechanisms behind noise pollution near airports.

Should I use fixed effects or random effects when I have fewer than five levels of a grouping factor in a mixed-effects model?

As linear mixed-effects models (LMMs) have become a widespread tool in ecology, the need to guide the use of such tools is increasingly important. One common guideline is that one needs at least five levels of the grouping variable associated with a random effect. Having so few levels makes the estimation of the variance of random effects terms (such as ecological sites, individuals, or populations) difficult, but it need not muddy one's ability to estimate fixed effects terms-which are often of primary interest in ecology. Here, I simulate datasets and fit simple models to show that having few random effects levels does not strongly influence the parameter estimates or uncertainty around those estimates for fixed effects terms-at least in the case presented here. Instead, the coverage probability of fixed effects estimates is sample size dependent. LMMs including low-level random effects terms may come at the expense of increased singular fits, but this did not appear to influence coverage probability or RMSE, except in low sample size (N = 30) scenarios. Thus, it may be acceptable to use fewer than five levels of random effects if one is not interested in making inferences about the random effects terms (i.e. when they are 'nuisance' parameters used to group non-independent data), but further work is needed to explore alternative scenarios. Given the widespread accessibility of LMMs in ecology and evolution, future simulation studies and further assessments of these statistical methods are necessary to understand the consequences both of violating and of routinely following simple guidelines.

Natural and anthropogenic noise increase vigilance and decrease foraging behaviors in song sparrows

Animals glean information about risk from their habitat. The acoustic environment is one such source of information, and is an important, yet understudied ecological axis. Although anthropogenic noise has become recently ubiquitous, risk mitigation behaviors have likely been shaped by natural noise over millennia. Listening animals have been shown to increase vigilance and decrease foraging in both natural and anthropogenic noise. However, direct comparisons could be informative to conservation and understanding evolutionary drivers of behavior in noise. Here, we used 27 song sparrows (Melospiza melodia) and 148 laboratory behavioral trials to assess foraging and vigilance behavior in both anthropogenic and natural noise sources. Using five acoustic environments (playbacks of roadway traffic, a whitewater river, a whitewater river shifted upwards in frequency, a river with the amplitude modulation of roadway traffic, and an ambient control), we attempt to parse out the acoustic characteristics that make a foraging habitat risky. We found that sparrows increased vigilance or decreased foraging in 4 of 6 behaviors when foraging in higher sound levels regardless of the noise source or variation in frequency and amplitude modulation. These responses may help explain previously reported declines in abundance of song sparrows exposed to playback of intense river noise. Our results imply that natural soundscapes have likely shaped behavior long before anthropogenic noise, and that high sound levels negatively affect the foraging-vigilance trade-off in most intense acoustic environments. Given the ever-increasing footprint of noise pollution, these results imply potential negative consequences for bird populations.

Anthropogenic noise affects insect and arachnid behavior, thus changing interactions within and between species

Urbanization and the by-product pollutants of anthropogenic activity pose unique threats to arthropods by altering their sensory environments. Sounds generated by human activities, like construction and road traffic, can oversaturate or interfere with biotic acoustic cues that regulate important ecological processes, such as trophic interactions and the coordination of mating. Here, we review recent work exploring how anthropogenic noise impacts inter-intra-specific interactions in insects and arachnids. We outline empirical frameworks for future research that integrate three mechanisms by which anthropogenic noise alters behavior through interference with acoustic cues: masking, distraction, and misleading. Additionally, we emphasize the need for experimental designs that more accurately replicate natural soundscapes. We encourage future investigations on the effects of developmental exposure to noise pollution and the impacts of multiple interacting sensory pollutants on insect and arachnid behavior.

Noise distracts foraging bats

Predators frequently must detect and localize their prey in challenging environments. Noisy environments have been prevalent across the evolutionary history of predator–prey relationships, but now with increasing anthropogenic activities noise is becoming a more prominent feature of many landscapes. Here, we use the gleaning pallid bat, Antrozous pallidus, to investigate the mechanism by which noise disrupts hunting behaviour. Noise can primarily function to mask—obscure by spectrally overlapping a cue of interest, or distract—occupy an animal's attentional or other cognitive resources. Using band-limited white noise treatments that either overlapped the frequencies of a prey cue or did not overlap this cue, we find evidence that distraction is a primary driver of reduced hunting efficacy in an acoustically mediated predator. Under exposure to both noise types successful prey localization declined by half, search time nearly tripled, and bats used 25% more sonar pulses than when hunting in ambient conditions. Overall, the pallid bat does not seem capable of compensating for environmental noise. These findings have implications for mitigation strategies, specifically the importance of reducing sources of noise on the landscape rather than attempting to reduce the bandwidth of anthropogenic noise.