From lab to field: Hearing and terrestrial communication in the endangered Hawaiian monk seal

The acoustic biology of Hawaiian monk seals (Neomonachus schauinslandi) is compelling from behavioral, evolutionary, and conservation perspectives. Until recently, descriptions of species-typical hearing abilities and vocal behavior were limited. Our research has sought to provide key amphibious bioacoustic data for this endangered species. To evaluate hearing in air and under water, we measured detection thresholds for narrowband tones with two individuals. The resulting audiograms indicate reduced hearing abilities relative to other seal species, with an especially notable insensitivity to airborne sounds. This suggests that terrestrial communication in Hawaiian monk seals is likely constrained by poor hearing. To explore this further, we estimated communication ranges for airborne vocalizations. We recorded spontaneous calls from free-ranging seals on an isolated beach to determine amplitude and spectral characteristics of vocalizations. When these data were combined with hearing thresholds and representative ambient noise levels, the resulting estimates suggested that terrestrial communication ranges are restricted to 100 m for female seals and their dependent pups. These findings update evolutionary considerations about hearing in seals and inform decision-making regarding anthropogenic noise exposures, supporting conservation efforts for Hawaiian monk seals.