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There is a global and growing concern with regard to anthropogenic noise impact on wildlife and natural habitats, but it is difficult to find consensus regarding scoping and assessment tools. This study adapts noise mapping procedures, common to most European countries, to a low traffic road (below 1000 vehicles per day) noise impact assessment in a breeding colony of the largest bird of prey in Europe. Results show that nest sites are located avoiding road traffic Leq levels higher than 40 dB. This means a road-effect zone of up to 500 m width from road margins, which previous scientific literature only refers in cases of traffic volumes higher than 10,000 vehicles per day. This finding is a noticeable impact by road traffic noise that reduces the breeding potential habitat more than 11% within the study area. This work shows the feasibility of expanding common methods and mapping tools for assessing and managing environmental noise in protected areas, which has worthwhile implications for both acoustics and conservation.

Anthropogenic noise is a growing ubiquitous and pervasive pollutant as well as a recognised stressor that spreads throughout natural ecosystems. However, there is still an urgent need for the assessment of noise impact on natural ecosystems. This article presents a multidisciplinary study which made it possible to isolate noise due to road traffic to evaluate it as a major driver of detrimental effects on wildlife populations. A new indicator has been defined: AcED (the acoustic escape distance) and faecal cortisol metabolites (FCM) were extracted from roe deer faecal samples as a validated indicator of physiological stress in animals moving around in two low-traffic roads that cross a National Park in Spain. Two key findings turned out to be relevant in this study: (i) road identity (i.e. road type defined by traffic volume and average speed) and AcED were the variables that best explained the FCM values observed in roe deer, and (ii) FCM concentration was positively related to increasing traffic volume (road type) and AcED values. Our results suggest that FCM analysis and noise mapping have shown themselves to be useful tools in multidisciplinary approaches and environmental monitoring. Furthermore, our findings aroused the suspicion that low-traffic roads (< 1000 vehicles per day) could be capable of causing higher habitat degradation than has been deemed until now.