Trends and knowledge gaps in field research investigating effects of anthropogenic noise.

Anthropogenic noise is a globally widespread sensory pollutant, recognised as having potentially adverse effects on function, demography, and physiology in wild animals. Human population growth, and associated changes in urbanisation, transportation, and resource extraction, all contribute to anthropogenic noise and are predicted to increase in the coming decades. As a result, wildlife exposure to anthropogenic noise is expected to rise correspondingly. Data collected by field research are uniquely important in advancing understanding of the real-world repercussions of human activity on wildlife. We therefore performed a comprehensive systematic review of literature published between 2008-2018 that reported field investigations of anthropogenic noise impacts. We evaluated publication metrics, geographical distribution, study subject, and methodology. Research activity increased markedly over the assessment period. However, there was a pronounced geographical bias in research, with most being conducted in North America or Europe, and a notable focus on terrestrial environments. Fewer than one-fifth of terrestrial studies were located in rural areas likely to experience urbanisation by 2030, meaning data on ecosystems most likely to be affected by future changes are not being gathered. There was also bias in the taxonomic groups investigated: most research was conducted on birds and aquatic mammals, whereas terrestrial mammals, reptiles, amphibians, fish, and invertebrates received only limited research attention. Almost all terrestrial studies examined diurnal species, despite evidence that nocturnality is the prevailing animal activity pattern. Nearly half the studies investigated effects of road or urban noise, with the bulk of research effort being restricted to functional, rather than physiological or demographic consequences. Few experimental studies addressed repercussions of longer-term exposure to anthropogenic noise, or longer-term post-exposure effects, and multiple noise-types or levels were rarely compared. These knowledge gaps will need to be tackled swiftly if we are to successfully manage effects of increasing worldwide wildlife exposure to anthropogenic noise. Article impact statement: Future field research into effects of noise pollution on wildlife must focus on underrepresented ecosystems, taxa, and activity patterns. This article is protected by copyright. All rights reserved.