The Jacobson or Vomeronasal Organ, an organ nested in the nasal area of snakes, lizards, many mammals, and hyraxes. It helps the animals detect organic compounds emanating from predators or prey as well as pheromones from other animals of the same species.

In both snakes and lizards, they flick their fork-shaped tongues up to “push” those chemicals onto their highly developed Jacobson organ. It is a specialized adaptation that allows for them to detect these compounds and pheromones directly.

Other animals, like horses, engage in a “Flehmen Response,” curling up their lips and tilting their heads back to take in airborne compounds through a passage in the front of their mouth into the nasal cavity. Unlike snakes, they rely on airflow to draw the scents in.

Hyraxes, meanwhile, have a very unique Vomeronasal Organ (VNO) . R. Broom, M.D. [3] discusses a key feature that differentiates hyraxes from some of the rest of these animals; that Hyraxes have a more “primitive” and robust nasal duct that makes the VNO more accessible through their nasal cavity than for many other mammals. They posses an unusually developed nasal-floor cartilage which forms a deeper channel for the VNO duct which might function even while the animal is chewing or vocalizing. This robust structural support suggests that hyraxes may rely more on their VNO than other mammals, though this has not been formally tested.

Hyraxes are rarely if ever seen engaging in the traditional Flehmen Response through raising their lips and tilting back their heads, and instead may use tongue movements to waft, stir, or sample scents towards their nostrils to increase what reaches the VNO through the nasal cavity. This could be evolutionarily explained by the lower airflow in the rocky crevices in which they make their homes as compared to many other mammals.

Their elephant cousins have been observed using the prehensile “finger” at the tip of their trunks to pick up substances and place them into their mouths, where chemosensory stimuli can reach their VNOs. [1] This elephant version of the Flehmen response uses the trunk rather than their lips to direct these chemicals. Hyraxes may employ a similar unorthodox approach to directing these compounds to their VNO passage. Though without a trunk, what might a rock hyrax use instead?

They might be using their tongues.

When rock hyraxes flick their tongues out, they generally extend their tongues out then curl it up towards their snout in a smooth repeated motion. Where dogs often use their tongues for thermoregulation by dropping them to allow for evaporation to cool their body temperature [4], the more focused and deliberate movement of a rock hyrax’s tongue implies a deeper purpose.

Given their more well-supported VNO with unusually robust nasal floors, as described by Broom [3], their tongue behavior becomes especially interesting. The deep cartilaginous channel around the rock hyrax’s VNO duct allows the animal to keep the duct open while screaming, squeezing into crevices, or chewing. But this development comes necessitates the use of their tongue to properly moisten the VNO duct while concentrating pheromones and chemicals towards the nasal cavity to enhance what reaches their VNO.

I propose calling this pattern the Câline Response: a possible tongue-nose behavior that helps hyraxes sample airborne chemicals and pheromones much more effectively, rather than simply cooling themselves or to communicate with other hyraxes.

Future work could test this hypothesis more rigorously. For example researchers could;

• Test the use of aerosol sprays and hyrax pheromones to quantify how often the rock hyrax engages in the Câline Response compared to control groups.
• Manipulate the ambient temperature and humidity of a hyrax enclosure to see whether tongue behavior tracks with thermoregulatory need.
• Present visual stimuli from other hyraxe to determine whether individuals showing more tongue movements elicit more significant responses.

Such experiments could help strengthen the idea of the Câline Response in use as a chemosensory behavior. Until then, it remains likely that the rock hyrax maneuvers its tongue to enhance its ability to detect pheromones and organic compounds through its nasal passage and Vomeronasal Organ.