Vacuum activities (or vacuum behaviours) are innate, fixed action patterns of animal behaviour that are performed in the absence of the external stimuli (releaser) that normally elicit them. This type of abnormal behaviour shows that a key stimulus is not always needed to produce an activity. Vacuum activities can be difficult to identify because it is necessary to determine whether any stimulus triggered the behaviour.
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."
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.
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.
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 dustbathing") is a behaviour performed by some birds when kept in cages with little or no access to litter. During sham dustbathing, 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 dustbathing, 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 "dustbathing" 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 dustbathing substrate, the term "sham dustbathing" is more appropriate.
- Russell A. Dewey, PhD. Psychology: An Introduction. Chapter 8: Vacuum, Displacement, and Redirected Activities.
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