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Abstract The efficacy of animal acoustic communication depends on signal transmission through an oft-cluttered environment. Anthropogenic-induced changes in vegetation may affect sound propagation and thus habitat quality, but few studies have explored this hypothesis. In the southwestern United States, fire suppression and cattle grazing have facilitated displacement of grasslands by pinyon-juniper woodlands. Northern grasshopper mice ( Onychomys leucogaster ) inhabit regions impacted by juniper encroachment and produce long-distance vocalizations to advertise their presence to conspecifics. In this study, we coupled acoustic recordings and electrophysiological measurements of hearing sensitivity from wild mice in the laboratory with sound transmission experiments of synthesized calls in the field to estimate the active space (maximum distance that stimuli are detected) of grasshopper mouse vocalizations. We found that mice can detect loud (85 dB SPL at 1 m) 11.6 kHz vocalizations at 28 dB SPL. Sound transmission experiments revealed that signal active space is approximately 50 m. However, we found no effect of woody plant encroachment on call propagation because juniper and woody plant density were inversely associated and both present barriers to a 9 cm mouse advertising at ground level. Our data indicate that woody plant encroachment does not directly impact the efficacy of grasshopper mouse communication, but vegetation shifts may negatively impact mice via alternative mechanisms. Identifying the maximum distance that vocalizations function provides an important metric to understand the ecological context of species-specific signalling and potential responses to environmental change. 

Acoustic communication is a fundamental component of mate and competitor recognition in a variety of taxa and requires animals to detect and differentiate among acoustic stimuli (Bradbury and Vehrencamp 2011). The matched filter hypothesis predicts a correspondence between peripheral auditory tuning of receivers and properties of species-specific acoustic signals, but few studies have assessed this relationship in rodents. We recorded vocalizations and measured auditory brainstem responses (ABRs) in northern grasshopper mice (Onychomys leucogaster), a species that produces long-distance calls to advertise their presence to rivals and potential mates. ABR data indicate the highest sensitivity (28.33 9.07 dB SPL re: 20 Pa) at 10 kHz, roughly corresponding to the fundamental frequency (11.6 ± 0.63 kHz) of longdistance calls produced by conspecifics. However, the frequency range of peripheral auditory sensitivity was broad (8-24 kHz), indicating the potential to detect both the harmonics of conspecific calls and vocalizations of sympatric heterospecifics. Our findings provide support for the matched filter hypothesis extended to include other ecologically relevant stimuli. Our study contributes important baseline information about the sensory ecology of a unique rodent to the study of sound perception.