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Effects of Noise on Wildlife

As human beings continue their encroachment upon the last remaining vestiges of untouched wilderness, wildlife populations around the globe continue to diminish in size. The impacts of human encroachment and environmental pollution are evident wherever research biologists perform their studies: loss of habitat and territory; loss of food supply; behavioral changes in mating predation and migration; and changes in interspecies relationships, altered predator-prey balance, increased competition for food and shelter.

Human-induced noise pollution is one of many factors contributing to the depletion of wildlife populations. Laboratory studies and limited field research have uncovered four major ways in which animals are adversely affected by noise pollution:

  • hearing loss, resulting from noise levels of 85 db or greater;
  • masking, which is the inability to hear important environmental cues and animal signals;
  • non-auditory physiological effects, such as increased heart rate and respiration and general stress reaction; and
  • behavioral effects, which vary greatly between species and noise characteristics, resulting in, for example, abandonment of territory and lost reproduction.

Studies on Rhesus Monkeys in the lab have shown that a 30% increase in blood pressure following exposure to as an average 85 db (lower at night, higher during the day) for eight months resulted in a permanently higher blood pressure and heart rate even after one month of quiet time!

Sound, stressed mice have been shown to be much more susceptible to disease, less able to learn mazes, and to experience 40-100% resorption of embryos and 66% reduction in fetal weight when exposed to 82-85 db (equivalent to a power lawn mower ) for eight hours per day.

Exposure of Desert Kangaroo Rats to dune buggy sounds (95 db at 4 meters, on and off for 500 seconds) caused a major reduction on detection distance for its principal predator the Sidewinder (Rattlesnake). In fact, the distance for the normal sand kicking response to the snake's presence was reduced from 40 cm. to 2 cm., and it took three weeks for the rat to recover. Surely in the field, this nocturnal rodent could not have survive at such a disadvantage!

Plenty of evidence exists to indicate that serious damage is occurring to animals in the wild. Long-term effects from medium to low level noise intrusion need much more study, with emphasis on threatened and endangered species. The synergistic effects of noise with other stressors on animals also need investigation.

Dave Cornman
Nature Sounds Society

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