Vacuum activities (or vacuum behaviors) are fixed actions of animals, which are triggered by inherited behavior patterns, although the usual key stimulus is absent.[1] This type of behavior shows that a key stimulus is not always needed to produce a behavior.[2] Vacuum activities are hard to identify because it is difficult to determine whether any stimulus triggered the behavior.
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The term was first established by the ethologist Konrad Lorenz in the 1930s after observations of a hand-raised starling.[3]
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 bird that catches flies snapped at the air when flying as if it were catching insects though there were no real insects there.
Weaverbirds go through complicated nest building behavior when there is no nest building material present.[4]
Adult cats that were weaned too early "suckle" exposed human skin when relaxed. Also, cat litterbox training is based on redirecting a vacuum activity (burying faeces to minimize scent exposure to potential rivals or prey; a usually unnecessary task for a housecat) into a productive habit for a pet.
Captive raccoons douse their food, which is most likely a vacuum activity based on foraging at shores.