# Exploring the Influence of Avian Vocal Presence on Appraisal of Urban Soundscapes
## 1 Introduction  
Human well-being in cities is partly determined by the acoustic environment, which has been changing in multiple ways in the past decades [1; 2; 3]. Noise pollution has been an important topic for society since it is clear that negative effects are spreading rapidly across different environments and across species [4; 5; 6; 7]. Environmental acoustics deals with noise and vibration caused by traffic, aircraft, industrial equipment, and recreational activities [8; 9]. Not only are there seriously detrimental effects for humans [10; 11], but anthropogenic noise is causing a serious loss of habitat, biodiversity, and natural soundscapes [5; 12; 13]. Consequently, approaching the noise pollution problem from just an acoustical point of view is not enough. There is a strong need for a multidisciplinary approach and collaboration between experts from different disciplines (e.g., acousticians, biologists, ecologists, urban planners, etc.) [5; 14]. City sounds typically contain a lot of traffic noise and frequent presence of human voices, for which we know well how they are appreciated by urban residents. From the human perspective, many people live in very noisy conditions and can often cope withthe constant presence of urban noise. However, exposure to exceptionally high and unpredictable levels of noise can have several negative consequences for human health, including both physical (e.g., respiratory agitation, racing pulse, high blood pressure, headaches) and psychological symptoms (e.g., attacks of stress, fatigue, depression, anxiety) [15; 16]. Furthermore, exposure to high noise levels can cause sleep, memory, and concentration disorders [17; 18; 19]. Acoustic appreciation of noisy urban conditions can improve by masking irritating or frustrating sounds or by the addition of appreciative sounds. Noisy activities of humans also affect animals and have caused, for example, a decline in bird diversity and abundance in urban and natural environments [5; 10; 11]. Given the continuous rise of the human population and the global spread of urbanization and anthropogenic noise, biodiversity conservation has become a global priority for policy makers; industry and nongovernmental organizations; and researchers of urban ecology, human perception, and well-being. Biodiversity not only has intrinsic value but is also beneficial for humans since many studies have shown that people find natural environments and the associated sounds pleasant and desirable (e.g., the sound of water or birds) [20; 21; 22; 23]. Our traffic noise may, therefore, have a direct negative impact on us, as well as an indirect one, through the impact of bird diversity loss and therefore, reduced vocal diversity. The vocal presence of birds can positively affect appreciation of urban soundscapes and increase the perceived soundscape restorativeness [24; 25], but few studies have addressed this psycho-acoustic hypothesis [26]. A convenient way to explore human perception of natural sounds in urban acoustic environments is by using the soundscape concept [27; 21; 28]. The soundscape consists of three components: biophony, including all natural sounds of animals; geophony, including all natural sounds of abiotic origin; and anthropony, including all sounds made by humans, human machinery, and activity [3]. The appreciation of a particular biophony component is best tested in the presence of realistic levels and diversity of both other components. The impact of the presence of birdsong, for example, can be tested experimentally by playback of natural recordings, which consist of most common anthropogenic sounds (e.g., traffic and human voices) together with some wind turbulence or rustling leaves, together with and without a bird singing. An adequate psycho-acoustic study on preference variation in urban soundscapes requires appropriate objective sound measurements of the test stimuli used for exposure.