It’s a known fact that musical talent can be seductive. But singing a ballad or playing an instrument only works if you’re good at it — and it looks like the same rules apply in the animal kingdom. Reproductive success in male rock hyraxes (Procavia capensis) is linked to their ability to maintain rhythm during courtship songs. In other words, males who can keep a tune are more likely to be successful in the mating market.
The importance of rhythm
Vlad Demartsev, who collected the data on the rock hyraxes while at Israel’s Tel Aviv University, has been studying hyraxes for 20 years. Hyraxes are social mammals with an extensive vocal repertoire that includes many “songs” performed by males. Each song has distinctive elements, which are combined into elaborate vocal displays.
Previous work by Demartsev and his colleagues showed that songs by hyraxes have an acoustic and temporal structure, which reflects signaler quality and social status. They also argued that song progression follows similar patterns to those used in human musical styles, aimed at keeping listeners attending and reaching a climactic ending.
“Their songs have regional dialects so individuals living in proximity sing more similarly to each other. They tend to sing in crescendo (getting louder as the song progresses) and reach peak complexity towards the end of their songs,” Demartsver said. “Rhythm has evolved so that animals that call in groups can better synchronize their songs.”
While they look like rodents, the hyrax actually has similar teeth, toes, and skull structure to that of an elephant — with which they share a common ancestor. Its strong molars grind up tough vegetation and two big incisor teeth grow out to be small tusks. There are three members of the hyrax family: rock, tree, and bush (or yellow-spotted) hyrax.
The rock hyrax is found along the coast of the Arabian Peninsula up to Lebanon. As their name suggests, they like to hang out in areas where there are boulders or rock formations. Their feet are built for rock climbing. The bottom of each foot is bare and has a moist pad that lifts up in the center for a suction effect to cling to most rocks.
They live in colonies of up to 50 individuals, sharing sleeping areas and looking for food together. Although males sign all year, the frequency peaks close and during the mating season in July or August. For males, copulation success depends on individual traits, and for women, on their previous reproductive success and role in the group.
Investigating the role of rhythm in courtship songs, Demartsev and his colleagues looked at the daily morning activities of hyrax communities between 2002 and 2013 in a natural reserve in Israel. They collected information on behaviors and vocalizations and then analyzed genetic information and audio recordings in their laboratory.
The findings showed that hyrax males keep a stable rhythm, with sounds happening at regular intervals. This is known as isochronous rhythm. Lee Koren, a study co-author, said the males who sang more frequently tend to have more surviving offspring. This is because some rhythms and stability are linked to reproductive success, Koren said.
The researchers believe that certain physiological weaknesses could have a negative effect on the ability of hyraxes to produce precise and rhythmic calls. This suggests that male hyrax courtship song rhythm could be an indicator of health and suitability as mates to prospective female partners, they wrote in the journal of Animal Ecology.
Studies have shown rhythm has now been shown to act as an indicator of individual quality in some species, while in others it helps in coordinating signals from different individuals within a group. Looking ahead, Demartsver said it would be “fascinating to compare animal species who sing individually and species that sing in groups.”