The discrimination of prey from non-prey. Most predators encounter a large number of different prey species that they have to discriminate from non-prey. The most commonly used cues are size, movement, and shape. Predators that have a choice of prey differing in size usually take the larger, as this is the most energy-efficient strategy. However, as size increases there usually comes a point beyond which the stimulus is no longer regarded as prey. Thus toads (Bufo bufo) respond positively to prey items within a specific size range, but actively avoid larger stimuli. The toad is able to judge the absolute size of the prey item by taking into account both the size of the image on the retina and the distance to the object. This is a matter of perceptual organization.
Movement of the prey-stimulus is essential for prey recognition in some species. The cuttlefish (Sepia officinalis) will normally only attack prawns that are moving, but if a prawn is taken from a cuttlefish that has just captured and paralysed it, then it will immediately be attacked again, even though it is motionless. The cuttlefish is now using an olfactory cue.
Prey recognition by shape is a complex matter, but a number of predators are known to use bilateral symmetry as a cue. Most living creatures are bilaterally symmetrical, whereas inanimate objects are not. Toads show prey-catching behaviour towards small, elongated objects, but avoid snake-like shapes with one end raised.
Subjects: Zoology and Animal Sciences.