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In general, a noise impact to wildlife can be determined by the degree to which the noise disrupts a functioning ecosystem.  Noise has the potential to affect wildlife in a variety of ways, varying between different types of animals.  Research shows that the degree of reaction to noise often varies with age, sex, season, situation, previous exposure to noise (habituation), noise level, and frequency spectrum. 

Potential noise effects on wildlife include; auditory damage, physiological changes, and behavioral alterations.  These effects are further characterized into primary and secondary effects.  Primary effects are direct physical effects to the animal.  Secondary effects are indirect changes which occur between the animal and its environment.  The following table and text describe these effects in more detail. 
 


Effects of Noise on Wildlife
 
  

 
Type of Effect Primary Secondary
 
Auditory Hearing Loss Change in Predator-Prey relationships
  Threshold Shift Mating Interference
    Reduction in Functioning
 
Physiological Stress Reduced Reproductive Capacity
  Metabolic Change Weakened Immune System
  Hormonal Change Reduction in Functioning
 
Behavioral Signal Masking Change in Predator-Prey relationships
  Avoidance Behavior  Population Reduction
    Migration and Loss of Habitat
    Mating Interference

 
  

Auditory Effects  -  Auditory effects are associated with very high noise levels (often in excess of 90 dBA) which typically only exist in laboratory settings.  These effects would involve hearing loss or threshold shifts which are a reduced sensitivity to sound similar to a partial hearing loss.  Threshold shifts have the potential interfere with communication and reduce an animal’s functioning ability.

Physiological Effects  -  Physiological effects, such as metabolic and hormonal changes, are often associated with stress.  Stress in wildlife in their natural setting is typically a difficult response to quantify.  For wildlife, stress reactions are part of survival and a routine occurrence.  Stress reactions involve what is commonly referred to as the “fight or flight” response.  When this reaction is inappropriate, such as fleeing from a non-threaten noise, impacts begin to occur.  Inappropriate reactions unnecessarily deplete an animal’s energy resources which can increase susceptibility to predators, disease, and starvation. 

Behavioral Effects  -  Changes in normal behavioral patterns are the most apparent effects of noise on wildlife.  When noise becomes an objectionable intrusion on wildlife habitats, these changes include alterations in habitat locations and migration patterns, and abnormal behavior that can cause difficulty in mating and survival. 

Summary

Noise has the greatest effect on wildlife which rely heavily on auditory signals for survival.  The frequency content of noise can be a factor for wildlife that use specific signals for establishing mating or territory.  Increases in background sound levels can interfere or mask communication signals used in mating or survival, which consequently could influence mating activity, population distributions, and detection of predators or prey. Noises that causes wildlife to startle or flee have the potential to deplete the animal's resources resulting in diminished performance and potential harm or injury.

It is important to note that numerous wildlife habitat areas exist in high-noise environments such airport runway areas and military installations. These areas often become wildlife habitats because human use is limited and or prohibited. For animals that migrate into these areas, the noise exposure may be less significant than the benefit of privacy and habitat these areas provide.