Effects: Birds and Noise Pollution

Next, I’d like to explore the effects of noise pollution on birds specifically. While many birds have long been exposed to loud natural sounds, anthropogenic noise pollution is a new phenomenon that birds have to cope with (Ortega, 2012).

There are multiple effects of noise pollution on birds, such as physical damage to their ears, stress responses, fright-flight responses, avoidant responses, changes in other behavioural responses e.g. foraging, changes in reproductive success, changes in vocal communication, interference with the ability to hear predators and other important sounds and potential changes in populations (Ortega, 2012). In particular, colonial bird species are more susceptible to noise – when one bird reacts, others will respond similarly.

Bird calls

Birds might change how their song sounds either by singing more loudly or changing the frequencies or timing of their songs. This is an example of how wildlife adapts to urban habitats.

Changing bird songs have implications for the ability to attract females for mating and securing territory for reproduction (Ortega, 2012). Data collected on bird nesting across the United States identified that human-produced noise affected birds that had calls of different pitches (Senzaki et al., 2020). Birds with low-frequency vocalisation such as the white-breasted nuthatch had calls that were of similar frequency to human noise, and thus human noise easily masked its calls, which could compromise its reproduction ability. On the other hand, the house wren, having a higher-pitch call frequency, was unaffected by noise (Senzaki et al., 2020). This suggests that anthropogenic noise pollution does compromise natural bird behaviour.

Noise masking is also an effect of noise pollution on bird calls. Masking occurs when sounds hide or interfere with the detection of bird calls, or sounds made by predators (Ortega, 2012). One study has also suggested that birds adjust the frequency of their calls by either increasing the lowest frequency with no change in the highest frequency (i.e. the range of their calls is decreased) or by shifting the entire vocalisation to a higher frequency (Ortega, 2012). Those with higher-pitched songs are less susceptible to noise pollution (Rheindt, 2003). Naturally, this has implications for the survival of certain species as birds utilise vocal communication to attract mates and defend their territories.

Specifically, the “dawn chorus” temporally overlaps with the heaviest commuter-traffic rush hours, which may determine habitat quality and reproductive success. The temporal shift of birds in cities singing earlier in the morning is attributed to light pollution, however, tropical birds experience little variations in day length, and hence, light. A study investigating the tropical species’ rufous-collared sparrows in Columbia, suggested that birds may sing earlier in noisy areas to avoid acoustic masking by traffic noise (Dorado-Correa, Rodríguez-Rocha and Brumm, 2016).

Reproductive Success

Noise pollution may also contribute to lowered reproductive success as the noise could affect the ability of birds to find or attract mates, and for parents to hear and respond to begging calls (Ortega, 2012). Noise may affect egg production, incubation, brooding, and predators. A study across highway infrastructure documented the disruption of between-species information transfer (Grade and Sieving, 2016). Titmice and chickadees are species that broadcast specific calls to alert other birds of predator threats, and other species may eavesdrop on these alarm calls to avoid predators. Recorded alarm calls were broadcasted to cardinals in natural areas near and far from highways – cardinals reliably produced predator avoidance responses in quiet areas, but those in noisy areas failed to respond (Grade and Sieving, 2016).

Other effects

Few studies have suggested a negative impact of noise on bird foraging. In Florida, a significant reduction in foraging was observed by five species of birds in the presence and absence of people (Ortega, 2012).

Investigating rainforest birds around Refugio Amazonas found that the birds responded strongly to noise treatments, with both visibility and vocalisation frequency decreasing in response to noise. In particular, insectivores, species that feed on insects, were strongly affected by noise (Karp and Guevara, 2010). This has consequences for ecotourism, which presents a more sustainable option compared to mass tourism, yet still has the potential to influence the natural environment. Noise reduction is hence a win-win for all stakeholders – wildlife, lodge owners and tourists, as silence would likely lead to tourists encountering more wildlife.

When environmental conditions change, natural selection favours bird calls that move effectively through the habitat (Ortega, 2012). As covered in earlier posts, noise does have health implications for humans. Naturally, high noise levels will also have negative consequences on the way birds function. Noise reduction and maintaining noise levels should be of top concern for us, as many higher-level noises are generated from anthropogenic sources.

 

References