Communication Masking by Man-Made Noise

Abstract

Conservationists and regulators are often challenged with determining the masking effects of man-made sound introduced into the environment. A considerable amount is known from laboratory studies of auditory masking of communication signals in birds, so that it is now feasible to develop a functional model for estimating the masking effects of noise on acoustic communication in natural environments not only for birds but for other animals as well. Broadband noise can affect the detection, discrimination, and recognition of sounds and whether acoustic communication is judged comfortable or challenged. Estimates of these effects can be obtained from a simple measure called the critical ratio. Critical ratio data are available in both humans and a wide variety of other animals. Because humans have smaller critical ratios (i.e., hear better in noise) than other animals, human listeners can be used as a crude proxy for estimating the limits of effects on animals. That is, if a human listener can barely hear a signal in noise in the environment, it is unlikely that an animal can hear it. The key to estimating the amount of masking from noise that can occur in animals in their natural habitats is in measuring or estimating the signal and noise levels precisely at the animal’s ears in complex environments. Once that is done, a surprising amount of comparative laboratory critical ratio data exists, especially for birds, from which it is possible to predict the effect of noise on acoustic communication. Although best developed for birds, these general principles should hold for all animals.