Noise pollution isn’t just affecting human city dwellers. Animals are also being impacted by the unintended byproduct of urbanization. In some cases, this can even lead to changes that are evolutionary in nature, as animals must learn to adapt to or avoid noisy environments.
The spread of urban noise is much greater than one might initially imagine. One recent study that took place in 22 national parks across the United States found that urban noise was audible about 28% of the time. Additionally, the World Health Organization has stated that being exposed to noises louder than 40 decibels on a regular basis can be damaging in the long run.
Animals frequently rely on sounds to locate food, avoid predators and find mates. With noise disruption, these activities are often interrupted. By using a variety of different observational techniques, scientists have been able to better understand just what kind of role human noise plays in the behavior of animals. Studies have shown that the effects are quite noticeable.
Most affected by human noise pollution are dolphins and songbirds. Both of these animals rely heavily on noise as a form of communication. Dolphins have been known to be affected by noises from ships, and these noises can cause disruptions to their foraging and physiological stress. In some cases, it can even cause marine animals to become stranded from their families. Additionally, crabs and eels that have been exposed to ship noise have been shown to express more anti-predator behaviors.
As for songbirds, noise pollution has led to a decline of bird populations in particularly noisy areas, such as around cities and along roadways. Some species have made adjustments to their vocal techniques so that their callings can be better differentiated from human noises.
For example, urbanized great tits have raised the frequency of their calls in order to reduce the acoustical masking that occurs in a predominantly low-frequency urban environment. Meanwhile, certain robins have managed to change the timing of their singing in order to coincide with quieter times of the day in cities. And black-chinned hummingbirds and house finches have actually chosen to settle in particularly noisy areas to avoid being detected by predators.
When exposed to road noise, prairie dogs have been shown to reduce their foraging efforts and increase their vigilance behavior. This could lead to long term population issues, especially when combined with other stressors for the prairie dogs, such as disease and habitat loss. Road noise has also been shown to affect the foraging efficiencies of bats, and it has led to changes in the vocal communications of frogs.
While more research needs to be done, it appears that human made noise is having an effect on more than just humans. Time will tell if animals will be able to adapt to the sounds produced by humans and their growing urban environments. This phenomenon might even lead to some very interesting evolutionary changes in the long term.