HRRBAA: Infrasonic Communication in a Cryptic Primate

There is widespread evidence that social and vocal complexity co-evolve: animals have larger repertoires of call types when they need to manage more long-term social relationships. By this logic, the very quiet L'Hoest's monkeys are an anomaly because, despite being highly social, they appear to produce only 10% of the expected number of call types. New preliminary evidence contradicts previous assumptions that this species is merely quiet. Instead, most of its communication may be concentrated within such low frequencies that they are inaudible to humans – i.e., infrasound. This study is designed to produce high-quality recordings of L'Hoest's monkey calls to document routine use of infrasound for within-group communication. The recordings can be disseminated through publicly accessible, online repositories. The data can inform future studies of physical mechanisms by which relatively small-bodied mammals produce and perceive such signals, the environmental and social pressures likely to have shaped this communication system, and whether related species also use infrasound. The project will advance training and mentoring of undergraduates, including individuals from underrepresented groups in STEM.

L'Hoest's monkeys face two conflicting challenges: as relatively small-bodied, terrestrial animals, they need to reduce the severe risk of predation by felids and other carnivores; yet the dense vegetation of their preferred habitats limits their visual contact with group-mates, necessitating reliance on acoustic signals to maintain group cohesion. This species may have adapted to these pressures through the use of low-frequency vocalizations that are likely to be inaudible to predators. Specialized equipment is necessary to create sound files as evidence of these signals and to explore their characteristics, because standard equipment is unable to reliably detect signals outside the range of human hearing. These audio files are paired with simultaneous video and distance measurements to nearby animals. Together, these records are used to (1) make a preliminary assessment of the number of call types that occur in the infrasonic (

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.