Effects of Noise Pollution on Urban Wildlife

THE PROBLEM

Noise pollution can potentially impact wildlife at the individual, population, species and community levels. These impacts occur in both urban and rural environments and, in some situations, could be a significant contributor to local and regional extinctions of small or geographically-confined populations. The overall impacts of anthropogenic (human-generated) noise are likely to increase significantly over at least the next few decades as urban areas expand into new areas, the human population increases in distribution and abundance, and human activities become more intensive and widespread. Therefore, there is an urgent need for ecological impact assessments to pay greater attention to noise impacts on wildlife, and to develop and implement more effective measures of avoiding or minimising them. There also needs to be scientifically-valid assessments of the effectiveness of these measures for each development or activity. This can be achieved through appropriate legislation and government regulation. Unfortunately, we seem to be moving in the opposite direction (i.e. less vigilant about disturbances, such as noise pollution, on the natural environment) because our environmental legislation, regulations and processes are becoming increasingly more bureaucratic (and less meaningful) and focused on habitat drivers of biodiversity protection (e.g. habitat protection and management, and biodiversity offsetting). While these drivers are important, they should not be pursued by ignoring or giving only momentary thought to other significant impacts.?

The present article identifies the main sources of anthropogenic noise, known impacts on wildlife at the individual, population and community levels, and discusses measures for avoiding or mitigating these impacts.

SOURCES OF NOISE POLLUTION

Transportation systems. Roads and their associated vehicular traffic, airports and aircraft, off-road vehicles, trains and ships. Although the land surface area of roads is relatively small, the ecological effects extend well beyond their boundaries. For instance, road traffic noise impacts about one-fifth of the land area of the United States.

Industry Noise e.g. refineries and factories, and oil and mining operations.

Construction and Demolition Noise. Noise from the construction and demolition of highways, roads, buildings and pedestrian walkways. Common sources of this form of noise include pneumatic drills and hammers, air compressors, bulldozers, trucks and pavement breakers.

Sport and Outdoor Entertainment Events e.g. ?high-speed racing car and rally car events, loud music events in outdoor stadiums and other outdoor public space areas, public activity in urban parks and fireworks displays.

Noise from Buildings. Examples of this kind of noise include loud music in the home, noisy social gatherings of people in outdoor areas, large air-conditioning units, electrical tools (e.g. electric saws and drills), garden maintenance equipment (e.g. lawnmowers), indoor electrical appliances and noisy pets (e.g. barking dogs).

Agricultural Noise. Use of farm machinery (e.g. bulldozers, harvesters) and pest deterrent acoustic systems (e.g. propane canons, sonic and ultrasonic devices).

Military Activity e.g. discharge of firearms, cannon-fire, explosions, low-flying aircraft.

Mobile Phone Towers, Traffic Control and Weather Radars and Wind Turbines. There is some evidence that the high sound frequencies emitted by mobile phone towers may interfere with the echolocation of bats, thus making it difficult for them to navigate and/or locate and capture prey.

Modification of Natural Environmental Sounds. Habitat clearing or thinning may also allow natural sounds such as those produced by wind, running water and the calls of animals to travel longer distances. In addition, urban structures may deflect, absorb or amplify natural sounds, thus preventing them from travelling great distances and echoing them to different areas.

Each source type varies in amplitude (loudness), frequency (pitch), spatial (distribution) and temporal patterns (timing, duration and predictability). There is both interspecific and intraspecific variation in the sensitivity and response to anthropogenic noise. A single individual may also vary its response temporally to anthropogenic noise. For instance, under different health and physiological conditions, age, life history stage, or due to past history of exposure to anthropogenic noise.

IMPACTS ON WILDLIFE

Overview

Loud noise has a greater impact on fauna than does quieter noise. Noise at frequencies that are similar to those used in vocalisations are most likely to interfere with animal communication and performance. Most anthropogenic noise is at low frequencies (less than 250 MHz), which can travel long distances with relatively little energy loss and is often difficult to avoid or mitigate. If a sound occurs at frequencies outside an organism’s hearing range, it will not have a direct impact. But if the organism can hear the sound, its acoustic energy could cause permanent or temporary hearing loss, but this might only occur when the animal is extremely close to the source of the noise.

It is often difficult to recognise the direct impacts of anthropogenic noise on fauna because they usually occur with other impacts such as increased human activity, vibration or habitat clearance, degradation and fragmentation. Even if an ecological investigator suspects that fauna are impacted by anthropogenic noise, it may not be obvious, and is often difficult to measure. An organism may show little or no response to noise in terms of habitat occupancy or foraging behaviour, but may experience strong negative impacts in terms of pairing success, number of offspring, physiological stress, or other measures of biological fitness. For instance, microchiropteran bats may roost successfully under wooden or concrete road and rail bridges by day, thus giving an ecological investigator the impression that they are not impacted significantly by traffic noise and vibration. But individuals within the colony may have elevated basal levels of circulating corticosteroids (stress hormones), which at sustained levels impact adversely on their health, longevity and reproductive success.

Behavioural Impacts

Most noise-related behavioural changes in wildlife involve:

1. Temporal changes in patterns of activity, e.g. songbirds singing at night when noise levels are lower than during daylight hours.
2. Altered spatial distribution or movements, usually expressed as site abandonment and decreased spatial abundance.
3. Decreased foraging and provisioning activities, which are usually coupled with increased vigilance and anti-predator behaviour.
4. Changes in mate attraction and territorial defence. In some bird species the strength of the pair bond is also weakened because females either have difficulty identifying the calls of their mates, or pair-bond strengthening calls are masked. Therefore, the females are more likely to copulate with extra-pair partners, which can change the genetic and social dynamics of a population, and ultimately the population’s biological fitness.

Health and Physiological Impacts.

Noise impacts on animals extend to the neuroendocrine system, reproduction and embryonic development, metabolism, cardiovascular health, cognition and sleep, hearing loss, a compromised immune system, and DNA integrity and gene expression. However, links between physiological, behavioural responses and fitness of a population are complex and remain understudied.

Faecal glucocorticoid metabolites (fGMs) in Northern Spotted Owls were elevated when the birds were exposed experimentally to motorcycle traffic and motorcycle noise. Elevated fGMs are a sign that the owls are physiologically-stressed. Spotted Owls nesting in areas with higher levels of traffic noise fledge fewer offspring. Sage Grouse on leks that were exposed experimentally to natural gas drilling noise or intermittent road noise also had elevated fGMs, inhibited social interactions and heightened vigilance for predators. These two examples suggest a possible causal link between anthropogenic noise, physiological stress and population fitness.

There are also likely temporal changes to physiological responses, e.g. circulating levels of stress hormone groups, such as catecholamines (adrenalin and noradrenalin) and steroid hormones (cortisol, corticosterone and aldosterone), may initially be elevated in response to noise, but subside as the individual becomes habituated to the disturbance.

Population Impacts

While anthropogenic noise impacts individuals, if enough individuals in a population are impacted by noise from a single development of activity, or the cumulative noise impacts of many developments, then it may have significant consequences at the population level. This can be manifested as a significant population decline, or a local or regional extinction. For instance, if a threatened species or population has already declined as a result of habitat loss, and then abandons otherwise suitable retained habitat to avoid anthropogenic noise, then its status could potentially become more critical. Reduced habitat use and lower breeding success has already been documented for species and populations subjected to sustained anthropogenic noise.

AVOIDANCE AND MITIGATION

The most common approach to minimising noise impacts associated with transportation, industrial activity and general urban environmental noise is the erection of physical barriers. But the effectiveness of these barriers is seldom monitored scientifically once installed, the barriers often extend only a short distance, and may compound habitat fragmentation impacts by restricting animal movements.

Other forms of noise management include limiting noise-generating activities to times when animals are less sensitive to noise disturbances (e.g. early evening or early morning periods, or outside breeding periods), and avoidance of loud noise in or adjacent to important wildlife habitat areas.

There also needs to be stricter noise standards that regulate for lower and more time-sensitive anthropogenic noise levels, and for the use of construction materials that absorb noise or deflect it away from noise-sensitive habitat areas.