The transmission of advertisement calls in Central American frogs

Acoustic communication signals change over distance due to loss of amplitude and fidelity, and it is assumed that signal degradation influences the receiver's ability to detect and decode signals. The degree of degradation depends on the signal's structure and the environment through which it transmits. We broadcast the advertisement calls of 22 species of Central American frogs at two heights within forested and open environments in Panama. We recorded these calls at five distances from the source and estimated signal degradation with a cross-correlation analysis, a measure that combines the effects of decrement in signal amplitude and fidelity. Calls degraded less when broadcast higher above the ground compared to on the ground, and less in open habitat compared to forested habitat; there was an additional interaction between height and environment. Furthermore, calls with low dominant frequencies experienced less degradation than calls with high dominant frequencies. There was no evidence, however, that the calls of these frogs have evolved to maximize habitat-specific transmission.