Anthropogenic Noise Affects the Bird Song Frequency and Behavioral Response: A Review

Abstract

Nowadays, as anthropological disturbance increases in animal’s life, they are adjusting their nature to a novel environment. Birds have also severe constrain on vocal communication by interfering with selection of acoustics signals. Noise from urban area affects negatively bird fitness with their communication and, for instance, activity related to breeding also had bad impact on predator detection. It influences also local distribution patterns as well as bird communities due to continuing exposure. Sometimes birds can survive with urban noise, but mechanism remains unknown. Here, we focused on relation between firstly anthropogenic noise and bird richness secondly noise level and song modification and then species noise tolerance and detection frequency. This kind of noise may hamper recognition of song by female, makes difficulties in territory marking, and also affects the maintenance of pair bond in birds. Studies on the quantification and documentation of acoustical characteristics and structural variability in birdsong provide substantial information on its conceptual and empirical significance. Songs may vary at local level in neighboring groups of birds and the level of variations depends on selection, based on various behavioral and ecological factors. So, it is important to understand the vocal communication for successful breeding for the conservation and for maintaining a balance within ecosystem.

1. Introduction

Avian habitat is becoming increasingly scarce due to rising populations. They have a deleterious impact on communication, territorial behavior, foraging, and reproduction in the entire animal community. The vocal cord of songbirds may be affected by anthropogenic interference as urbanization increases in cities. Higher-frequency song of blackbird (Turdus merula) components had greater amplitudes as well, and city birds tended to sing higher-frequency (and consequently higher amplitude) song elements over forest species [1]. Anthropogenic noise is a pervasive pollutant that changes how animals communicate acoustically. Some animals adjust their vocalizations in response to environmental noise. There is still much to discover about how much adjustment efficacy varies depending on the source of the noise, if signal adjustments improve communication in noise, and how individual physiology variance varies depending on reaction time. After assessing each subject’s adrenocortical response, songs that had been modified for noise and those that had not been modified were played to wild Savannah Sparrows (Passerculus sandwichensis). Under some altered acoustic conditions, the playback of songs that were rewritten for loud surroundings was able to successfully reestablish suitable conspecific territorial hostile behavior [2].

Finding a link between adrenocortical responsiveness levels that reduced communication mistakes in some types of infrastructure and increased errors in others was unanticipated. Song alterations that worked well at pump jacks did not function well at screw pumps for persons with poorer adrenocortical reactivity and vice versa. These results demonstrate that vocal adaptations can sometimes compensate for communication gaps caused by environmental noise, but physiological variations among receivers may limit the use of these adaptations. Mitigation strategies must consider both the acoustic and physiological effects of infrastructure in order to reduce anthropogenic noise.

Acoustic communication can be disrupted by noise, which can then have an impact on signaling behavior and the development of acoustic communication [3]. The Lombard effect, cultural transmission, an unintentional change in vocal effort, or a decisive action by the signaler are examples of mechanisms of selection that can result in changes in acoustic behavior as a result of efforts to enhance signal detection and discrimination in the presence of background noise (e.g. adjustment in timing of vocalization) [4, 5, 6]. Immediate signaling flexibility (ISF), a context-dependent type of behavioral plasticity, enables animals to change their acoustic behavior momentarily in response to changes in background noise. This can involve adjusting the amplitude, spectral or temporal features of acoustic signals, or the timing of signaling behavior [7, 8]. However, the way and degree to which the signal is altered vary between and within species depending on the species’ capacity for behavioral flexibility, developmental plasticity, and micro-evolutionary responses as well as the flexibility of the signaler, their own flexibility, their past experiences, and their perception of noise [9].

2. Amplitude increases with frequency

Nemeth found that in the frequency range of up to 2.2 kHz, blackbird song components clearly showed a positive association between frequency and amplitude. The amplitude varied significantly with frequency; for instance, the average maximum amplitude level increased by more than 15 dB from 1.5 to 2.5 kHz. Blackbird song showed a coupling between peak frequency and amplitude, and city birds tended to sing higher-frequency components that can be produced at louder sound intensities. Both the raised frequency and the corresponding increase in amplitude lessen the acoustic masking caused by low-frequency traffic noise, but the frequency-dependent amplitude change has a stronger impact. City birds may be able to sing at larger amplitudes to lessen acoustic masking by noise by selecting higher elements [10]. This discovery supports earlier research that found positive relationships between frequency and amplitude in other songbird species [11]. This finding implies that nearby mechanisms, such as physical impedances [12], biophysical constraints [13], or physiological restraints [14], maybe what prevent the production of loud vocalizations at the lower end of the frequency range.

Noise’s detrimental effects on reproduction may be linked to its effects on communication. Anthropogenic noise may be interfering with mating selection due to masking effects and the need to modify communication [15]. Additionally, we are aware that parental and child interaction is crucial for the survival of the latter [16]. For instance, begging is a behavior used by nesting passerine birds to signal their need for food. Begging involves a combination of postures and sounds.

Studies have indicated that anthropogenic airborne noise affects auditory communication [17]. Synthetic traffic stimuli (spectral peak: 10 Hz) elicited a call-rate change at a lower threshold than synthetic wind-turbine playbacks, whereas the former did not (spectral peak: 100 Hz).

3. Discussion

It is hypothesized that noise sources that are both novel or unpredictable and related to a physiologically significant sound will elicit reactions resembling those linked to predation risk [18]. Therefore, cutting back on or stopping calling could increase the likelihood of avoiding the predator’s attention. Furthermore, compared to a multimodal stimulus, a particular univocal stimulus supplied to the animals may be ineffective [19]. No matter the reason, a drop in calling rate can have repercussions. Numerous scientists have claimed that elevated airborne noise levels have negative effects on animal communication during mating, which can affect reproductive success [20]. It also has a negative impact on species interaction within population and male–female response and playback song behavior.

According to projections, an additional two billion people will require a place to live in the next 20 years, but they will not reside in the existing cities but rather in newly built urban regions [21]. Rare species are typically negatively impacted by urbanization, while more widespread species that can include native generalist species but frequently refers to non-native urban colonizers are favored [22, 23, 24, 25]. Diversified urban ecology does offer a wide range of niches, therefore urbanization does not always result in a loss of species diversity [26]. However, on a broader scale, urbanization results in homogenization and a loss of diversity since, regardless of the original fauna, typical urban species end up being the same everywhere [27, 28]. Urban problems may be particularly stressful for animals that still exist in cities and outside of them, as evidenced, for example, by a divergence in heterophil-leucocyte ratios [29] or elevated baseline corticosterone levels in male birds in urban habitats [30].

However, despite the fact that many species leave cities because they depend on habitat elements that no longer exist, others find a new home among the bricks and concrete and adjust to life in the city [31]. Many animal groups utilize acoustic signaling to protect their territories, alert conspecifics to oncoming predators, or attract mates [32]. Individual fitness and population persistence may suffer from any changes to the transmission environment that prevent acoustic signals from reaching the intended receiver or alter the information content of the signal. Chronic noise exposure is a result of expanding transportation networks, resource exploitation, motorized recreation, and urban expansion, even in the most remote wilderness locations [33, 34]. Only if signalers change the form of their songs or if receivers are able to shift their perceptual apparatuses in reaction to background noise can effective animal communication be maintained in altered auditory settings [9]. When background noise and a particular species’ auditory output coincide in their frequency spectra at a specific time and location, acoustic masking may result.

Animals frequently employ acoustic communication to share information among themselves. It is done by using an auditory signal that is produced by a sender, travels through the environment, and is picked up by a receptor [35]. Acoustic waves can travel great distances and carry data, including the sender’s identity, position, and sexual orientation. Their use is appropriate in a variety of situations, such as luring mates for breeding, defending one’s territory, and warning of danger. Interactions between communicators are hampered when the communication process is inefficient from signal emission to signal reception. Thus avian species in urban climates have a high frequency in their song in comparison to non-urban climates. They have to produce high pitch sounds for a song, affect male–female interaction and behavioral responses due to anthropogenic noise, and somehow indirectly affect the breeding.

4. Conclusion

Anthropogenic noise is a category of sound that can interfere with communication and be viewed as a form of environmental pollution. The next critical step in determining the true ecological effects of noise pollution is more research into how species in the wild not only detect but also distinguish between signals within noise gradients. Therefore, it is crucial to comprehend how noise pollution might contribute to further habitat degradation for sensitive species already suffering from habitat loss and climate change, as well as how ecological effects from acoustic environment modification compare to anthropogenic effects that have drawn ecologists’ attention for a longer period of time. In the future, we propose developing studies to disentangle the distinctions between distraction and masking, to investigate how an organism’s behavior may be influenced by anthropogenic noise that is outside of its vocal range. To examine how a greater variety of song types affect issues of detection and discrimination and to better understand demographic effects, we also recommend including examples with vocal qualities that deviate from normative conditions. According to playback trials, anthropogenic vibratory stimuli significantly decreased the calling activity in focused males, with their mean call rate falling by 50%. Vibrations from wind turbines and vehicles had an equivalent effect on call volume. The results of comparing the prerecorded and artificial stimuli show that the whole vibrational spectrum, not just its peak frequency, was responsible for the observed responses. Additionally, playback of naturally recorded audio decreased the sound strength threshold at which animals changed their baseline calling behavior and other interaction in populations toward each other. Future research, particularly field-based experiments in appropriate systems, will allow for a better understanding of the full extent of anthropogenic noise’s effects on species and communities, how the acoustic environment has changed in comparison to other well-studied human-induced habitat modifications, and how these effects might be mitigated through avian conservation measures that could be viewed as a form of environmental pollution and that could potentially help.