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Sounds are more easily transmitted underwater than through air and many freshwater fish species can hear them, particularly over the low frequencies. Recent studies on freshwater fish evidenced that hearing sensitivities can be limited by the level of ambient noise, a phenomenon also known as acoustic masking. However, it is still unclear whether variations in ambient noises, such as those produced by human activities, may alter fish trophic interactions.The general objective of this study was to propose and evaluate a theoretical framework explicitly linking fish attack rates to species hearing sensitivities and ambient noise levels in freshwater ecosystems. The proposed model shows that the feeding activity of fish at an intermediate position in the food web is conditional on the probability of being acoustically detected by their predators, or of encountering an acoustically distressed resource.Model simulations and preliminary field results suggest that yellow perch (Perca flavescens) could feed more actively in the presence of augmented ambient noise levels. Yellow perch captures per unit effort were higher by a factor of 2.7 in noisy versus quiet days. We argue that fish exposed to intermediate levels of noise could maximise the probability of detecting food patches while minimising their predation risk.Acoustic monitoring programmes for freshwater ecosystems require a fundamental knowledge of underwater noise levels, species hearing sensitivities and features affecting sound propagation. The approach proposed in this paper is seminal in linking the above descriptors in a coherent mathematical framework to understand the effect of underwater sounds on trophic interactions. Such framework is needed to make testable predictions and generalise to other taxa and ecological contexts. [ABSTRACT FROM AUTHOR]

Anthropogenic noise has been shown to alter the transmission environment and distort acoustic signals, prompting vocalizing species to use compensatory mechanisms. Through a meta-analysis we investigated the relative importance of biological and contextual factors predisposing species to shift their singing/calling frequencies in response to anthropogenic noise. We gathered data from 36 studies, synthesizing information on more than 160 experiments and 60 bird and anuran species. To estimate the breadth of frequency shift, we calculated a standardized effect size using Hedges' g. We fitted a multilevel linear mixed-effect model on g as the dependent variable weighted by its inverse variance, with typical frequency, body mass, experimental condition, and noise source type as independent terms. Our results reveal broader shifts in smaller bird species when compared with bigger species, an effect that was emphasized in the low-frequency component of the song spectrum. Birds increased their dominant frequencies when confronted to anthropogenic noise, whereas anurans were less prone to such shifts. Human-altered acoustic environments can be considered a novel selective force impelling change to the communication patterns of many vocalizing species. [ABSTRACT FROM AUTHOR]