The Flehmen response is a distinctive animal behavior involving a unique facial expression used to enhance scent perception. This behavior often appears as a pronounced grimace where the animal curls back its upper lip, exposing its front teeth and gums. The term originates from the German word flehmen, which translates to “to bare the upper teeth”. This action is a specialized method of gathering and analyzing specific chemical signals, allowing various species to gather information beyond what is possible through regular sniffing.
How the Flehmen Response Works
The physical act begins when an animal encounters an interesting scent, often causing it to momentarily cease breathing while its head is raised and held still. The curling of the upper lip then creates a specific pathway, which is necessary to transfer scent molecules directly to a specialized sensory organ. This action pulls air and non-volatile compounds into the vomeronasal organ (VNO), also known as Jacobson’s organ.
The vomeronasal organ is an auxiliary olfactory structure located in the nasal cavity, or in the roof of the mouth, depending on the species. In mammals exhibiting the Flehmen response, this organ connects to the oral cavity via small ducts situated just behind the incisor teeth on the upper palate. The grimacing movement effectively channels the scent particles, often dissolved in moisture, through these ducts and directly into the VNO.
Once inside the VNO, specialized sensory neurons detect the chemical signals, bypassing the main olfactory system. The VNO is adapted to analyze these moisture-borne chemical signals. This accessory olfactory system then sends signals to the accessory olfactory bulb in the brain, which targets areas like the hypothalamus and amygdala to trigger appropriate behavioral responses.
The Primary Goal of This Behavior
The fundamental purpose of the Flehmen response is the detection and analysis of non-volatile organic compounds, primarily pheromones. Unlike airborne odors, pheromones convey specific biological information between individuals of the same species. The VNO perceives these signals, which are often found in urine, feces, or glandular secretions.
This chemical intelligence is used for numerous aspects of social and reproductive life. Males frequently use the response to determine the reproductive status of females, checking if a potential mate is in estrus or “heat.” The analysis of pheromones allows animals to assess a female’s reproductive condition for successful mating.
Beyond reproduction, the Flehmen response aids in various other forms of intraspecies communication. Animals use it to recognize territory markings left by rivals, helping them avoid conflict or identify competitors. It is also employed for individual recognition, allowing animals to distinguish between familiar group members and unfamiliar individuals.
Which Animals Use Flehmen
The Flehmen response is a widespread behavior observed across a diverse range of mammalian species. It is particularly prominent among ungulates (hoofed animals) and felids (the cat family). Domestic horses are one of the most recognizable examples, where a stallion will perform a dramatic, prolonged upper lip curl after investigating a mare’s urine.
The behavior is common in livestock such as goats, sheep, and cattle, and in exotic ungulates like giraffes, tapirs, and rhinoceros. Felines, from house cats to large predators like lions and tigers, also exhibit this grimace when analyzing scents. While a horse’s response is a full, open-mouthed curl, a cat’s expression is often more subtle, appearing as a slight opening of the mouth. Other species like llamas, elephants, and some canines also utilize this method.