Effects of Vegetation Structure on Communication Distance in Ecologically Distinct Vocal Rodents and Implications for Conservation

Abstract

Long-distance acoustic signals mediate important social interactions between vocal animals, and the structure of the environment can influence sound transmission to impact communication distance. Vocalizing from positions that optimize transmission is one key solution to minimizing environmental attenuation, though few studies assess the magnitude of this effect in relation to receiver position. In our first study, we assessed how transmission of high-frequency vocalizations produced by semi-arboreal pinyon mice (Peromyscus truei) varied based on the position of senders and receivers in a receding ecosystem. We found that vocalizations showed less attenuation when both senders and receivers were elevated at the same height, and when receivers were elevated, regardless of sender height. The results of this first study highlight the importance of considering receiver position in animal communication, especially when senders produce highly directional signals. In our second study, we assessed how anthropogenic disturbances such as fire suppression can alter forest structure and impact sound attenuation patterns. In the spruce-fir and mixed-conifer forests of the Pinaleño Mountains that harbor endangered Mt. Graham red squirrels (Tamiasciurus fremonti grahamensis), numerous historical anthropogenic disturbances have altered forest characteristics and contributed to habitat degradation and loss. We assessed how recent forest restoration influenced the attenuation of red squirrel territorial rattle vocalizations in three treatments; thinning, understory fuel reduction, and untreated control plots. Across all treatments, we found that increasing stand densities resulted in higher attenuation, with ca. 6 dB difference between the highest and lowest stand density plots. Additionally, rattles on untreated control plots experienced more attenuation than thinned and fuel-reduced plots. A lidar-derived measure of canopy structure was as effective in explaining variation in rattle attenuation as on-the-ground measurements. Results of the second study indicate that forest restoration can impact the efficacy of acoustic communication and that integration of sensory ecology and remote sensing can inform wildlife conservation.