The transmission of advertisement calls in Central American frogs

Acoustic communication signals change over distance due to lossof amplitude and fidelity, and it is assumed that signal degradationinfluences the receiver's ability to detect and decode signals.The degree of degradation depends on the signal's structureand the environment through which it transmits. We broadcastthe advertisement calls of 22 species of Central American frogsat two heights within forested and open environments in Panama. Werecorded these calls at five distances from the source and estimatedsignal degradation with a cross-correlation analysis, a measurethat combines the effects of decrement in signal amplitude andfidelity. Calls degraded less when broadcast higher above theground compared to on the ground, and less in open habitat comparedto forested habitat; there was an additional interaction betweenheight and environment. Furthermore, calls with low dominant frequenciesexperienced less degradation than calls with high dominant frequencies.There was no evidence, however, that the calls of these frogs haveevolved to maximize habitat-specific transmission.