Tactical deception in animals, also called functional deception, is the use by an animal of signals or displays from an animal's normal repertoire to mislead or deceive another individual.
Definition Tactical or functional deception is the use of signals or displays from an animal's normal repertoire to mislead or deceive another individual. Some researchers limit this term to intraspecific behaviour, meaning that it occurs between members of the same species.
Relation to cognitive ability Tactical deception has been used as a measure of advanced social cognition, as it relates to brain function. Primates have larger brains, relative to body size, than in any other mammal except for dolphins, and this size difference is mainly due to an enlarged neocortex. Research has suggested that the evolution of the primate brain is selected-for in highly social species. One study used 18 species with varying brain volumes (three strepsirrhines, four New World monkeys, seven Old World monkeys, and four ape species). The study used the frequency of tactical deception as a measure of social cognition, and it found a strong correlation between the use of social deception and size of the neocortex.
Taxonomic range
Cephalopods Among cephalopods, some colour changes in cuttlefish might be called tactical deception, as these fish sometimes present entirely different displays to two different observers. When a male cuttlefish courts a female in the presence of other males, he displays a male pattern facing the female (courtship), and a female pattern facing away, to deceive other males.
Birds In an anecdotal account, Simmons reported that a female marsh harrier courted a male to obtain access to food he had stored. She then took this food and fed it to chicks that had been fathered by another male. More extensive studies focused on possibly deceitful behaviour in the pied flycatcher, a species in which males may possess more than one territory. Females gain from mating with a male that has no other mates and males may try to deceive females about their mating status (mated or unmated). Females frequently visit the male, and if he is always alone on his territory he is probably unmated. Thus, by repeated sampling of male behaviour, females are usually able to avoid mating with previously mated males. Group-foraging common ravens hoard their food in a number of places, and also raid the caches made by others. Cachers withdraw from conspecifics when hiding their food and usually place their caches behind structures, out of sight of potential observers. Raiders remain inconspicuous, keeping at a distance from cachers near their cache sites, but within sight. In response, cachers often interrupt caching, change cache sites, or empty their caches. These behaviours suggest that ravens can withhold information about their intentions, which may qualify as tactical deception. Similarly, if a Eurasian jay (Garrulus glandarius) is being watched by another jay, it tends to cache food behind an opaque barrier rather than a transparent barrier, apparently to reduce the likelihood of other jays pilfering their caches.
Mammals In domestic pigs, in a setting where the behaviour of a trained animal could reveal the source of food to another animal, the trained animal spent longer at the food source before other pigs arrived. Intentional tactical deception has been proposed for mice. In particular, d'Isa et al. have observed that free-living black-striped mice (Apodemus agrarius) perform a peculiar deceptive dodging maneuver to escape from a chaser mouse. The chased black-striped mice enters a single-entrance chamber, hides inside the chamber next to the entrance, waits until the chaser has entered and then, exploiting the distraction of the back-turned chaser, takes the exit to escape in the opposite direction.
Primates Observations on great apes have been widely reported as evidence of tactical deception. Several great apes have been trained to use sign language, and in some instances these animals seem to have used language in an attempt to deceive human observers. Koko, a female gorilla, was trained to use a form of American Sign Language. It has been claimed that she once tore a steel sink out of its moorings and when her handlers confronted her, Koko signed "cat did it" and pointed at her innocent pet kitten. Nim Chimpsky was a common chimpanzee trained in American Sign Language. Trainers claimed that when Nim grew bored of learning to sign words, she would sign 'dirty' indicating she wanted to go to the toilet, which caused the trainer to stop the lesson. Another example involves a chimpanzee approached from behind by a loud aggressive rival. Here, the chimpanzee moved his lips until he lost his fear grin thereby concealing his fear. Only then did he turn around to face the challenger. Deceit in great apes has been studied under experimental conditions, one of which is summarised by Kirkpatrick:
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