The flehmen response involves an animal curling its upper lip back to expose its front teeth, inhaling with nostrils closed, and holding this position for several seconds.
Also known as flehmen position, flehmen reaction, flehmen grimace, or flehming.
Origin
The term "flehmen" comes from the German verb flehmen, meaning "to bare the upper teeth".
First introduced in 1930 by Karl Max Schneider, a director at the Leipzig zoo.
Initially described by Frederik Ruysch in 1732 and Ludwig Jacobson in 1813.
Function and Mechanism
Purpose: Transfers pheromones and other scents into the vomeronasal organ (VNO or Jacobson's organ), aiding in scent detection.
The VNO is an auxiliary olfactory sense organ crucial for processing chemical signals.
Mechanism: Involves drawing air into the VNO via a duct behind the front teeth.
Organ Development: Well-developed in mammals like cats and horses.
Chemical Cues
Detects non-volatile organic compounds (non-VOCs), such as pheromones and hormones from the animal's genital regions or urine.
Occurrence
Exhibited by a wide range of mammals, including ungulates and felids.
Common in domestic cats and horses.
In horses, it may indicate discomfort if occurring outside typical contexts.
Intra-species Communication
Reproductive Status: Used by males to identify reproductive states of females via pheromones.
Reproductive Synchrony: Synchronizes reproductive events among females, e.g., in sable antelope and American bison.
Post-parturition: Seen in mares after birth, reacting to newborn foals and amniotic fluids.
Immature Animals: Young animals such as horses and elephants perform flehmen, indicating early VNO maturity.
Inter-species Communication
Response to Various Species: Tested in goats with urine from 20 different species, indicating an interspecific pheromone trigger.
Observed in a range of mammals, including domestic cats, giraffes, elephants, and more.
Notable Observations
Horses: Strong response to odors from mares in estrus.
Giraffes: Includes urine tasting as part of the response.
Elephants: Use trunk "finger" to transfer stimuli to VNO.