Abstract
In this paper we describe the masking of pure tones in humans and birds by manmade noises and show that similar ideas can be applied when considering the potential effects of noise on fishes, as well as other aquatic vertebrates. Results from many studies on humans and birds, both in the field and in the laboratory, show that published critical ratios can be used to predict the masked thresholds for pure tones when maskers consist of complex manmade and natural noises. We argue from these data that a single, simple measure, the species critical ratio, can be used to estimate the effect of manmade environmental noises on the perception of communication and other biologically relevant sounds. We also reason that if this principle holds for species as diverse as humans and birds, it probably also applies for all other vertebrates, including fishes.