We are delighted to share our new paper, “Honestly exaggerated: howler monkey roars are reliable signals of body size and behaviourally relevant to listeners”, out Open Access in Animal Behaviour.
Howler monkeys produce extremely loud, low-frequency roars that exaggerate the impression of body size relative to other species. But do roars still carry reliable information about size within a species, and do other howlers pay attention to it?
Working with black and gold howler monkeys (Alouatta caraya), we found that larger males produce roars with lower formant spacing, making formants an honest cue to body size. In playback experiments with 23 listeners, using roars that simulated small, average and large males, howlers looked towards the speaker for longer and were more likely to approach roars from simulated larger males.
Together, these results show that formants advertise body size and mediate social interactions in howler monkeys, with potential roles in assessing rivals and choosing mates.
Huge thanks to our coauthors Eloise Pedersen, Holly Farmer, Philippa Dobbs, Tecumseh Fitch, David Reby and Ben Charlton!
Dunn JC, Pedersen E, Farmer H, Dobbs P, Fitch WT, Reby D, Charlton B (2026). Honestly exaggerated: howler monkey roars are reliable signals of body size and behaviourally relevant to listeners. Animal Behaviour 231: 123424. https://doi.org/10.1016/j.anbehav.2025.123424
