Indeed, noise pollution has a dramatic impact on habitat selection, foraging patterns and communication networks of animals (anurans: Bee & Swanson, 2007 Grace & Noss, 2018 birds: Swaddle & Page, 2007 terrestrial mammals: Shannon et al., 2014 marine mammals: Nowacek et al., 2007 McMullen, Schmidt & Kunc, 2014) with serious implications for their survival and reproduction (reviewed in Brumm & Slabbekoorn, 2005 Blickley & Patricelli, 2010 Brumm, 2013 McGregor et al., 2013). Anthropophony can alter the behavior, phenotype and homeostasis of animals living near or within the cities, with potential effects at a population level ( McGregor et al., 2013 Giraudeau et al., 2014). Anthropophony is closely associated with human activity routine, from construction and mass recreation to transportation (aerial, terrestrial and marine), the latter being considered as one of the most pervasive acoustic perturbations on Earth ( Barber, Crooks & Fristrup, 2010 Shannon et al., 2016). Although urban habitats may provide benefits to city-dwelling animals, such as greater food availability and less exposure to natural predators ( Muhly et al., 2011 Adams, 2016), anthropogenic disturbances often have detrimental consequences on wildlife ( Ciuti et al., 2012 Hendry, Gotanda & Svensson, 2017 Palacios, D’Amico & Bertellotti, 2018), which has given rise to a field of research known as “urban wildlife ecology” that aims to understand the effects of human disturbance on animal populations that live within the cities or close to human settlements ( Gill, Sutherland & Watkinson, 1996 Frid & Dill, 2002 Magle et al., 2012 Gaynor et al., 2018).įor many organisms, an omnipresent source of stress is represented by anthropogenic sound ( Slabbekoorn et al., 2018 Kunc & Schmidt, 2019 Raboin & Elias, 2019), also called anthropophony ( Pijanowski et al., 2011). Owing to the constant expansion of cities and deforestation around the world, humans have increasingly invaded wildlife habitats, reshaping the landscape into man-altered ecosystems ( Hendry, Gotanda & Svensson, 2017). Our study thus indicates reduced alarm calling through habituation to human presence and suggests a titis’ resilience to anthropogenic noise with little evidence of physiological stress. Finally, titis’ response to the mannequin varied according to our expectation, with alarm calling being greater in distant groups relative to highway.
Validated enzyme-immunoassays of fecal samples however detected surprisingly low cortisol concentrations, unrelated to the changes observed in the RMS and M indices. Focal sampling analysis revealed that the time spent moving by adult pairs was inversely correlated with noise, the behavioral change occurring within a gradient of minimum sound pressures ranging from 44 dB(A) to 52 dB(A). Study groups resided in small, overlapping home ranges and they spent most of their time resting and preferentially used the lower forest stratum for traveling and the higher levels for foraging. Sound pressure measurements and systematic monitoring of soundscape inside the titis’ home ranges confirmed the presence of a noise gradient, best characterized by the root-mean-square (RMS) and median amplitude (M) acoustic indices importantly, both anthropogenic noise and human presence co-varied. We hypothesized that groups of titi monkeys exposed to higher levels of anthropogenic noise and human presence would react weakly to the mannequin and show higher concentrations of fecal cortisol compared with groups in least perturbed areas. We mapped group movements, sampled the titis’ behavior, collected fecal samples from each study group and conducted experiments in which we used a mannequin simulating a human intrusion in their home range. We studied six family groups of titis residing at increasing distances from a busy highway, in a park promoting ecotourism near Santa Cruz de la Sierra, Bolivia. Yet, little is known to what extent these animals can tolerate anthropogenic noise arising from roadway traffic and human presence in their habitat. Worldwide urban expansion and deforestation have caused a rapid decline of non-human primates in recent decades.
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