February 18, 2017

The 3 A's of Coping with Anthropogenic Noise

Animals use their cognitive abilities to respond to anthropogenic noise in three different ways: avoidance, adjustment, and adaptation.
By JoAnna Pendergrass, DVM
Anthropogenic noise (e.g., road traffic, industrial noise) is generated by human activity. This type of noise, which can affect animals’ acoustic communication, has altered the natural landscape since the industrial age. Compared with natural noise sources (eg, water, wind, animals), anthropogenic noise has more energy; this energy can vary over time or stay consistent.
How anthropogenic noise affects animals has become an increasingly popular research topic involving multiple fields of study. To date, most anthropogenic noise studies have used birds, given that acoustic communication in birds is essential to their survival and reproduction. However, the effects of anthropogenic noise have also been studied in other species, including marine mammals and amphibians.
The Effect of Anthropogenic Noise on Animal Cognition
Anthropogenic noise affects an animal’s behavior and hearing abilities. Exposure to chronic, elevated anthropogenic noise can damage an animal’s eardrums, leading to temporary or permanent hearing loss. This hearing loss can affect an animal’s ability to perceive and respond to acoustic signals effectively.
Whether anthropogenic noise is a stressor remains under debate. Studies have reported the negative effects of elevated glucocorticoid levels, indicative of a stress response, on cognition in animals. Other studies investigating a potential link between anthropogenic noise and long-term elevated glucocorticoid levels, though, have reported conflicting results. As the author noted, “The link between noise, elevated glucocorticoids and cognition is still as yet primarily theoretical.”
The relationship between chronic noise and neurotransmission has also been evaluated. Rats exposed to chronic noise have demonstrated spatial memory loss, indicated by increased levels of the excitatory neurotransmitter glutamate in the hippocampus. Chronic noise exposure has also caused sleeplessness and depression in rats, likely due to altered neurotransmission. Despite these findings, it is not yet known how and why chronic noise affects neurotransmission; the effect of chronic noise on cognitive neural pathways also remains unknown.
Coping Mechanism #1: Avoidance
Avoidance, either spatial or temporal, is one type of coping mechanism for anthropogenic noise. Studies have reported animals establishing habitats away from noisy areas; notably, species richness is low near roadsides. How animals decide to actively avoid noisy areas is unknown. It is possible that they perceive anthropogenic noise as a predator threat.
Temporally, animals avoid anthropogenic noise by communicating during noise gaps, known as “gap calling behavior.” Because anthropogenic noise can mask acoustic communication, animals use their cognition to perceive noise volume and decide when to make acoustic signals.
Coping Mechanism #2: Adjustment
Animals that cannot avoid loud anthropogenic noise can make immediate or long-term behavioral adjustments. Immediate adjustments include making louder acoustic signals or, in the case of songbirds, adjusting song type; the neural mechanisms underlying these adjustments are unknown. Long-term adjustments resemble acclimation and are learned through repeated trial and error.
Learning to make these adjustments indicates behavioral phenotypic plasticity, or the ability to adjust phenotypic behavior according to environmental changes. Such plasticity can affect how well an individual or population can thrive in a noisy environment when noise avoidance is not feasible.
Coping Mechanism #3: Adaptation
Animals can adapt to anthropogenic noise by selecting which acoustic signals will be most effective in certain environments. This adaptation occurs over multiple generations but is more likely to be cultural than genetic. Whether anthropogenic noise directly selects for heritable traits is unknown.
Overall, cognition’s role in how wild animals respond to anthropogenic noise requires further investigation. As the author wrote, “Progress in this field is ongoing, and our current knowledge provides a solid foundation from which to pursue many exciting opportunities.”

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