Anonymity versus individual recognition in animals’ communities

There are many reasons for individual recognition in animal societies including territoriality, reciprocal altruism, monogamous pairing, and maintaining hierarchy. Lorenz’ (1966) at first sight paradoxical view that “aggression is impossible without love” is really based on the notion of address space. Specimens are able to sort their relationships out if they know each other “personally”. The concept of Machiavellian intelligence, presented by deWaal (1982), and Byrne and Whiten (1988), refer to intellectual ability to deal with social situations and to change tactics creatively as the game progresses. Such a system of social navigation is characteristic for primates’ societies, and is based on members’ awareness about characters and habits of their mates and their abilities to predict possible reactions of individuals to events and actions of others. Broom (2003) considers individual recognition between members of societies of group living species a necessary condition for development of morality and religion.

From the experimenters’ point of view, individual recognition is a cognitive process whereby an animal becomes familiar with a conspecific and later discriminates it from other familiar individuals.

Individually distinct cues have been demonstrated in a variety of mammals as well as in several bird species (for review see Mateo, 2004, 2006).

There are many studies of social species which indicate that they discriminate between individuals of their own species and in some cases remember them even if they are absent for months or even years. Among primates, humans are good at remembering other members of their own species. An average person can recognise (in the sense of knowing whether they have seen it before) about 2000 faces. Judging by differential behavioural (usually vocalisations or threat) responses in face matching tasks chimpanzees could do this at least for 50 different examples of faces (Parr and deWaal, 1999; Parr et al., 2000).

At the same time, complex social behaviour can be based on mechanisms which do not require individual recognition. Even to concur congruently within teams there is no need to know each other personally. It is possible to interact as team members being only informed about functions of agents. Anonymous communities such as fish shoals and bird flocks are capable of complex coherent behaviour. In particular, they can act as coordinated groups against predators. For instance, flocks of starlings when meeting with a sparrow-hawk, group together, push on to meet the predator, flow around it and then gather again after its tail. For their turn, predators usually do not attack an individual within a group; instead, they wait for a chance to catch a member of the group that gets lost.

Were Nature arranged more simply one could suggest that anonymity is typical for primitive societies, and that increasing of complexity of social organisation in the Animal Kingdom corresponds to the increasing of complexity of both nervous systems and behaviour in general. In reality, the picture is variegated. For example, in the class of birds, swans, gees and sweeps enjoy intimate personal inter-relations whereas at least some species of storks and herons are known as not recognising each others. A mouse can remember the odours of another mouse they have only been in contact with for 2 minutes for 5-7 days and mice are able to distinguish between 12 of individual conspecifics presented simultaneously. A rat can only remember each rat they encounter for about an hour (Eichenbaum, 2004). Like many social insects, rats strongly distinguish members of their colony from strangers and react to other rats in a very aggressive manner whereas individual recognition seems to play a little role in their social life (Lorenz, 1966). It is worth noting that discrimination between nestmates and strangers can be based on rather complex processes. For example, nestmate recognition in the social Hymenoptera is by colony scent, which turns out to be a complex gestalt of hydrocarbons absorbed into the outer cuticle of the exoskeleton, shared by food exchange and grooming, learned by imprinting, and largely independent of kinship in composition (Wilson and Hö lldobler, 2005).

Invertebrates are usually thought to be incapable of individually identifying conspecifics. Nevertheless, there are at least some evidences of complex behavioural interactions between individuals which are probably based on individual recognition. This is not astonishing after those feats of intelligence of social hymenopterans which were described earlier in this book.

Field experiments with Formica pratensis ants showed that “frontier guards” in neighbouring ants’ families identify each other at least as members of small “guard groups” (Reznikova, 1974, 1982). The matter concerns constant ants’ units patrolling bounds of their feeding territories. To test the hypothesis that members of these groups recognise each other, ants were attached by thin “lashes” to inscribed object-plates. Inscriptions informed the researchers that some ants are taken from the same or from an alien family; some of alien ants are frontier guards (taken from the corresponding plots of ants’ territories) hypothetically acquainted to the guards of the family tested, whereas others are strangers taken from the remote places of the feeding territory of the alien family (Fig. X-1). It turned out that the ants do not touch members of their own family, excitedly feel all over alien but possibly acquainted guards from the neighbouring family, and kill all ants that were taken from the remote places of the neighbouring territory. Since ants definitely can not read inscriptions, it is very likely that they can easily distinguish between acquainted guards and strangers. Besides pratensis several other ant species can be expected as possessing the same system of recognition; the great majority of ants use much more simple “strangers-no strangers” system of identification.

Similar experiments have revealed the same effect in vertebrates species such as Oscines (Falls, Brooks, 1975), salamanders (Temeles, 1994), beavers (Bjǿ rkǿ yli and Rosell, 2002) and others. This system of identification underlies the so-called Dear Enemy Hypothesis (DEH): personally acquainted neighbours establish boundaries, split resources, and form a temporal society in which balance is based on sharing informative signals (Godard, 1991; Fox and Baird, 1992). Many social species such as monkeys, hyenas, wild dogs and others behave in a way which indicates recognition of members of neighbouring social groups.

There are several evidences that individual “face-control” based on higher level of recognition exists in invertebrate species that interact in a stable prolonged cohesion. The first example came from desert wood-louses. These Crustacean burrow in pairs and recognise each other by tactile examination of the location of aciculae on partners’ body (Marikovskii, 1969; Linsenmaier, 1987). In the paper wasp Polistes fuscatus queens and workers use yellow facial and abdominal patterns to visually identify individual nest mates (Fig. X-2). Individuals whose yellow markings were experimentally altered with paint received more aggression than control wasps painted in a way that did not alter their markings. In addition, aggression to wasps with experimentally altered markings declines significantly over time, suggesting that it is the unfamiliarity of the new markings rather than something else about the new markings that caused the aggression (Tibbetts, 2002, 2004). Ants of highly social species working in “teams”, or “cliques” possibly use individual recognition to work effectively in complex situations (Reznikova and Ryabko, 2003). We will consider this case in Chapter 35.

In long-living social species tight cohesion in societies can be based on highly developed capacities for social recognition. For instance, African elephants can recognise and remember six hundred other individuals (Poole and Moss, 1983). Play-back experiments carried out in Kenya by McComb et al. (2000, 2001) have established that female elephants may be able to recognise about 100 different individuals by their acoustic signals and in some cases even remember them for 12 years. Discriminatory abilities in this case seem to improve with age. Female elephants travel around in small social groups led by a matriarch. These groups may meet up with a dozen or more other groups at different times while traversing the ranges of their habitat. To prevent hostilities and reduce possible stress or panic it is important for the elephants to know whether the groups they are meeting is a potential threat or not. Researchers found that the older matriarchs (of about 55+ years old) were able to respond in these play back experiments with a greater degree of association between the calls they recognised and the exact degree of familiarity they had with the caller.

There are several limitations of individual recognition in animals’ societies. For example, as it was noted in Part IX, in play back experiments with vervet monkeys, where the call of one mother’s infant is played to the troop, many of monkeys will look in the direction of the mother whose baby has called. Recognising and responding to relationships between other individuals is a very advanced level of social evolution (Cheney and Seyfarth, 1990). The laughing hyena represents one of non-primate species with a high level of group organisation that would appear to demand individual recognition skills. Indeed, playback experiments have confirmed that mothers in this species respond differentially to the “whoop” calls produced by their cubs. There is also some indication that they can recognise the voices of other individuals within the clan.

The basic capacity of individual social recognition seems to be widely spread in animals. We do not know yet whether an ant can distinguish a face of another familiar ant if its portrait is rotated in front of it from front to profile but sheep seem to be capable of it. Kendrick and colleagues (Kendrick and Baldwin, 1987; Kendrick et al., 1995, 2001) applied several behavioural approaches to examine whether sheep can distinguish between categories of individuals and the extent to which they can actually identify specific individuals by their faces. Researchers constructed a choice maze apparatus that allowed sheep to choose between face images in order to gain access to the real individual whose face-picture had been seen. The sheep were shown pairs of faces that had different attraction to them (i.e. sheep vs human; familiar vs unfamiliar animal or breed; male vs female). The sheep chose sheep faces over human ones and familiar sheep faces over unfamiliar ones. Another way of testing the potential for using mental imagery is to train the animals to discriminate between pairs of familiar or unfamiliar faces by the frontal image and then to switch suddenly the images used to profile views (or vice versa). The sheep continue to get the task right when the face views are changed. This shows both that they know it is the act of recognising a particular individual rather than a particular view of their face that gets them a reward (i.e. true individual recognition) and that they may be able to mentally rotate the image of the face from front to profile in order to match a front view with a profile one. Another set of experiments showed that sheep can divide pictures of conscpecifics’ faces into emotionally distinct categories. They can distinguish whether faces had horns and how big they were - an important index of dominance and gender; whether faces were of members of the same breed and how familiar they were - sheep prefer the company of their own breed and are known to strike up long-term individual friendships; whether faces were from species that could pose a threat- humans and dogs. This face recognition system in sheep is mainly designed for identifying categories of individuals that have a specific emotional significance. It implies close interactions between the brain systems dealing with detection of faces and those associated with making emotional responses. Interestingly it is often just this link that appears to break down in human individuals with schizophrenia and autism.

Cognitively demanding individual recognition in animals’ societies can be implemented on different kinds of individual traits including olfactory cues. It has been experimentally demonstrated on Belding’s ground squirrels Spermophilus beldingi, group living borrowing rodents found in Alpine regions of the western United States. They live up to 12 years, therefore there is a potential for them to interact repeatedly and recognise individuals. These animalsproduce a number of cues that are individually distinct, including odours from oral, dorsal, pedal and anal glands and from ears (Fig. X-3). Mateo (2006) has used habituation-discrimination tasks (see Chapter 6) to determine which odours are individually distinct. In this task, an animal is repeatedly presented with a particular stimulus (here, an individual’s odour) until it habituates to it, and then an animal is presented with a novel stimulus (here, another individual’s odour) to determine whether the animal dishabituates to it, indicating discrimination of the two stimuli. A variant of the task was used to determine whether S. beldingi form multiple representations of familiar individuals. That is, does the knowledge of an odour from a familiar individual generalise to other odours of that individual (produced from other glands). Subjects were habituated to one odour collected from Individual 1, and were then tested with the odour from a second source collected from Individual 1 and the same odour source from Individual 2. If ground squirrels recognise individuals as a whole, rather than just remember their separate odours, they should generalise among several odours of an individual and dishabituate (show an increased response) only to odours of another individual. The obtained results suggest that ground squirrels incorporate multiple odours into their memories of conspecifics and thus form a mental representation of familiar individuals.

In sum, there are many studies not only of such acknowledged highly social and intellectual species as primates, elephants and dolphins, but also of pigs, sheep, dogs, pigeons, ground squirrels and some others which indicate that they can discriminate between individuals of their own species and other species, can behave in a consistently different way towards various members of their social group, and can use the information in a way which suggests that they have concepts of individuals and of some of their qualities (Broom. 2003). Knowing whether species members live in anonymous or in individualised social space we can judge about their behaviour more exactly and even use this for practice. For instance, Albright (1978) recommended that herds of one hundred or more cattle should be split into smaller groups on the basis that it is difficult for the cattle to recognise and remember more than seventy to one hundred individuals. Anthropologist Dunbar (1996) suggests that human beings should reach a " natural" cognitive limit when group size reaches about 150. There is extensive empirical evidence of social groupings of about this size in the anthropological literature. Many companies organise working space basing on these projections of social limits.