Recognition of Degraded Signals in the Gray Treefrog (Hyla chrysoscelis)

Abstract

For many animals such as frogs and toads, auditory communication is critically important in conveying information regarding an organism's species, location, and quality. However, interference and distortion caused by biotic and abiotic factors in the environment can degrade acoustic signals. The amount of degradation that occurs largely depends on the distance separating the sender and receiver (degradation increases as distance increases). In this experiment, I examined how female gray treefrogs (Hyla chrysoscelis) respond to degraded male calls. I subjected females to a series of playback tests consisting of synthetic male calls that varied in amplitude modulation depth (poorly modulated calls are considered to be temporally degraded) and overall intensity (simulates different separation distances). I tested two alternative hypotheses regarding how females will respond to degraded calls at different simulated distances. One hypothesis is that females will be more tolerant of degraded calls when they are played at low intensities (simulating a large separation distance) because degradation is expected to occur in the natural environment when the signal has traveled any significant distance. The alternative hypothesis is that females will be unresponsive towards degraded calls of low intensity because it is not worth the energy investment required to travel to the "far away" male when the female is unable to accurately assess his quality due to call degradation. The results from this experiment support the hypothesis that females are more responsive to poorly modulated calls when they are played at an overall lower intensity.