Underwater signal attenuation of northern red-legged frog calls

Abstract

Shallow water acoustics can dramatically alter spectral profiles of the northern red-legged frog underwater advertisement calls and should be taken into consideration when designing man-made aquatic environments as part of habitat mitigation. While much is known about atmospheric constraints on acoustic communication, we need to learn more about aquatic constraints. What is known about underwater acoustic signal transmission is garnered primarily from deep ocean research, leaving much to be discovered about the relatively extreme shallow underwater environments such as exists in ponds. The northern red-legged frog, Rana aurora, is one of three ranid species shown to vocalize while submerged underwater, and only one of two known to use the underwater portion of its environment for mating. My hydrophone recordings of the underwater chorus include calls with dominant frequencies in the 5000—15000 Hz range, sharply contrasting with the established dominant frequency range for advertisement calls of the northern red-legged frog of 450–1300 Hz. I conducted frequency sweep playbacks at breeding which demonstrate that shallow residential water bodies have unique frequency responses that dramatically alter the spectral profiles of underwater signals. This changes the frequency characteristics of what is heard by females and could significantly impact reproductive success.