Whiskers - Function

Function

Generally, vibrissae are considered to mediate a tactile sense, complementary to the tactile sense offered by skin. This is presumed to be advantageous in particular to animals that cannot always rely on sight to navigate or to find food (for example, nocturnal animals). The function of vibrissae is a very active research area—experiments to establish the capabilities of whiskers use a variety of techniques, including deprivation of the whisker sense (typically by trimming whiskers, which soon grow back) and temporary deprivation of other senses by careful equipment design. Experiments to date suggest that whiskers are required for, or contribute to: object localization, orienting of the snout, detection of movement, texture discrimination, shape discrimination, exploration, thigmotaxis, locomotion, maintenance of equilibrium, maze learning, swimming, locating food pellets, locating food animals, and fighting, as well as reading of water currents in marine mammals and nipple attachment and huddling in rat pups. Sensing function aside, movements of the vibrissae may indicate something of the state of mind of the animal, and the whiskers play a role in social behaviour in rats.

Whisking—the periodic movement of the whiskers—is also presumed to serve tactile sensing in some way. However, exactly why an animal might be driven "to beat the night with sticks", as one researcher once put it, is a matter of debate, and the answer is probably multi-faceted. Scholarpedia offers:

"Since rapid movement of the vibrissae consumes energy, and has required the evolution of specialised musculature, it can be assumed that whisking must convey some sensory advantages to the animal. Likely benefits are that it provides more degrees of freedom for sensor positioning, that it allows the animal to sample a larger volume of space with a given density of whiskers, and that it allows control over the velocity with which the whiskers contact surfaces."

Animals that do not whisk, but have motile whiskers, presumably also gain some advantage from the investment in musculature. Dorothy Souza, in her book "Look What Whiskers Can Do" reports some whisker movement during prey capture (in cats, in this case):

"Whiskers bend forward as the cat pounces. Teeth grasp the mouse tightly around its neck. The cat holds on until the prey stops wriggling."

Whilst contact with the whiskers is the most obvious stimulus to evoke a behavioural response, air currents are also effective. Indeed, some aquatic mammals (such as seals) probably make the most use of their whiskers in detecting water currents, which enables them to follow the path of an object that 'swam' ahead several minutes past and even to discriminate the species and/or size of the fish responsible for the trail.

Anecdotally, it is often stated that cats use their whiskers to gauge whether an opening is wide enough for their body to pass through (e.g. Why Do Cats Have Whiskers?, Cat Behaviour Explained). This is sometimes supported by the statement that the whiskers of individual cats extend out to about the same width as the cat's body, but at least two informal reports indicate that whisker length is genetically determined and does not vary as the cat grows thinner or fatter. Certainly, rats have been shown in the laboratory to be able to accurately (within 5-10%) discriminate the size of an opening, so it seems likely that cats can use their whiskers for this task. However, reports of cats (particularly, kittens) with their heads firmly stuck in some discarded receptacle are commonplace (e.g. Cops save kitten with head stuck in can) indicating that, if a cat has this information available, it doesn't always make best use of it.