Date Published: February 13, 2019
Publisher: Public Library of Science
Author(s): Timothy J. Boycott, Jingyi Gao, Megan D. Gall, William David Halliday.
The efficacy of animal signals is strongly influenced by the structure of the habitat in which they are propagating. In recent years, the habitat structure of temperate forests has been increasingly subject to modifications from foraging by white-tailed deer (Odocoileus virginianus). Increasing deer numbers and the accompanying browsing have been shown to alter vegetation structure and thus the foraging, roosting, and breeding habitats of many species. However, despite a large body of literature on the effects of vegetation structure on sound propagation, we do not yet know what impact deer browsing may have on acoustic communication. Here we used playback experiments to determine whether sound fidelity and amplitude of white noise, pure tones, and trills differed between deer-browsed and deer-excluded plots. We found that sound fidelity, but not amplitude, differed between habitats, with deer-browsed habitats having greater sound fidelity than deer-excluded habitats. Difference in sound propagation characteristics between the two habitats could alter the efficacy of acoustic communication through plasticity, cultural evolution or local adaptation, in turn influencing vocally-mediated behaviors (e.g. agonistic, parent-offspring, mate selection). Reduced signal degradation suggests vocalizations may retain more information, improving the transfer of information to both intended and unintended receivers. Overall, our results suggest that deer browsing impacts sound propagation in temperate deciduous forest, although much work remains to be done on the potential impacts on communication.
Animal communication involves the production of a signal by a sender, the transmission of that signal through the environment, and the detection of that signal by a receiver . The efficacy component of animal signals is determined, in large part, by the transmission properties of the signaling environment [1,2]. The sound propagation characteristics of habitats therefore play a key role in the evolution of vocal signals. Selection pressures often favor acoustic signals that minimize degradation and attenuation; thus enhancing the propagation of signals and optimizing communication in a given environment (Acoustic Adaptation Hypothesis; [3,4]). Changes to the sound propagation characteristics of an environment could, therefore, alter the selection pressures on the efficacy components of signals, driving changes to the structure of signals over time [3–6].
Overall, we found that sound propagation is altered in deer-browsed habitats. Our study only looked at sound propagation over short distances and thus our results are most applicable to short distance communication signals, such as those used in courtship, agonistic encounters, or parent-offspring communication. We used artificial sound stimuli to assess how basic sound propagation characteristics were influenced by deer browsing. However, bird songs and calls vary greatly in their structure and different species may be affected differently by deer browsing. Thus, future studies investigating species-specific propagation patterns would be very interesting. Altogether, our results suggest that there may be a surprising connection between deer-induced habitat alteration and animal communication. Future work should investigate the differences in soundscapes among habitats with different levels of deer browsing, as well as investigate the production and reception of acoustic communication signals in avian populations that are found in habitats with different levels of deer browsing. Furthermore, it may be informative to investigate sound propagation over greater distances that would be representative of long distance communication.