Not complete. I plan on adding more detail and hypotheses to the functional explanations section.

Original article: Vacuum Activity

Vacuum activities (or vacuum behaviours) are innate, fixed action patterns that are produced in the absence of the external stimuli (or releaser) that normally elicits them. These types of behaviours normally take place when an animal is placed in captivity and no longer perceives a particular stimulus, so it carries out the corresponding behaviour unprompted.

Animals that were raised without releasing instinctual behaviours, due to being in captivity or being taken as a pet, will produce these behaviours in seemingly random moments due to a build-up of energy reserves.^[1] Lorenz also proposed animals receive pleasure when carrying out instinctive habits.^[1]

Lorenz also considered the use of vacuum activities by all animals as an evolutionary attribute allowing them to produce the correct behaviour in a given situation, assuming they have no knowledge of when the behaviour would work best.^[1]

From Latin vacuum (an empty space, void) noun use of neuter of vacuus (empty) related to vacare (be empty).

The term was first established by the ethologist Konrad Lorenz in the 1930s after observations of a hand-raised starling. In 1937 Lorenz wrote: "With head and eyes the bird made a motion as though following a flying insect with its gaze; its posture tautened; it took off, snapped, returned to its perch, and with its bill performed the sideways lashing, tossing motions with which many insectivorous birds slay their prey against whatever they happen to be sitting upon. Then the starling swallowed several times, whereupon its closely laid plumage loosened up somewhat, and there often ensued a quivering reflex, exactly as it does after real satiation."

Wild raccoons often investigate their food by rubbing it between their paws while holding the food underwater, giving the appearance of 'washing' the food (although the exact motivation for this behaviour is disputed). Captive raccoons sometimes perform these actions of 'washing' their food by rubbing it between their paws, even when there is no water available. This is most likely a vacuum activity based on foraging behaviour at shorelines.

Squirrels that have lived in metal cages without bedding all their lives do all the actions that a wild squirrel does when burying a nut. It scratches at the metal floor as if digging a hole, it acts as if it were taking a nut to the place where it scratched though there is no nut, then it pats the metal floor as if covering an imaginary buried nut.

Lorenz observed that a starling bird snapped at the air when flying as if it were catching insects though there were no real insects there.

Weaver birds go through complicated nest building behaviour when there is no nest building material present.

One vacuum activity that has been studied is 'tongue-rolling' by calves. Calves raised for 'white' veal are generally fed a milk-like diet from birth until they are slaughtered at about four months of age. The calves are prevented from consuming roughage such as grass or hay partly because the iron contained in such plant-based food would cause their muscles to assume a normal reddish colour instead of the pale colour that purchasers of this product demand. The diet, however, is unnatural because calves would normally start to forage and ruminate from about two weeks of age. When limited to a milky diet, some calves will spend hours per day in what appears to be 'vacuum grazing'. They extend the tongue out of the mouth and curl it to the side in what appears to be the action that cattle use to grasp a sward of grass and pull it into the mouth, but the calves do this simply in the air, without the tongue contacting any physical object.."

A similar vacuum activity to tongue rolling is 'vacuum chewing' by pigs. In this behaviour, pigs perform all the activities associated with chewing but with no substrate in their mouth. This abnormal behaviour can represent 52–80% of all stereotyped behaviours.

Sham dustbathing (sometimes referred to as "vacuum dust bathing") is a behaviour performed by some birds when kept in cages with little or no access to litter. During sham dust bathing, the birds perform all the elements of normal dust bathing, but in the complete absence of any substrate. This behaviour often has all the activities and temporal patterns of normal dust bathing, i.e. the bird initially scratches and bill-rakes at the ground, then erects her feathers and squats. Once lying down, the behaviour contains four main elements: vertical wing-shaking, head rubbing, bill-raking and scratching with one leg. However, hens "dust bathing" on wire floors commonly perform this close to the feed trough where they can peck and bill-rake in the food. Because it seems the birds appear to treat the feed as a dust bathing substrate, the term "sham dust bathing" is more appropriate.