Introduction

It is often assumed by pet owners that domestic cats are similar to dogs in their social behaviour and will easily tolerate, or even 'need,' close social contact with conspecifics. However, cats have a very different evolutionary past from dogs and very different social needs. The domestic cat is a unique species in terms of social behaviour, as it has an essentially asocial ancestral species but has subsequently adapted to living in social groups. However, because their ability to live in social groups is a very recent development in evolutionary terms, cats' repertoire of visual and vocal communication behaviours is limited. In particular, they do not display appeasement or conflict reducing signals. This means that although cats can live together very successfully within established social groups, they only do so in circumstances where competition over resources is minimised, such as occurs naturally in feral or farm colonies. Problems often arise in the context of multi-cat households, where competition over resources is created, and where cats that do not perceive each other as part of the same social group live in close proximity to each other. Stress caused by the presence of other cats is the greatest cause of problem behaviour in domestic cats.

Evolutionary History

The common ancestor of the domestic cat was the African Wild Cat (Felis silvestris lybica). This wild cat, which is still found today, is a solitary nocturnal hunter, with individuals being well dispersed across the savannah because of the relatively sparse concentration of rodent prey in that environment. Individual cats maintain and defend a hunting territory from conspecifics because access to sufficient rodent prey is essential for survival in this environment.

Cats were first domesticated in Egypt approximately 4–6,000 years ago. It is likely that cats originally started to live near settlements because of the large numbers of rodents living in association with the Egyptians' grain stores. These cats would have not only altered their foraging habits for this 'easy' food, but there would also have been a selection pressure for increased tolerance of man. In addition, the cats would have been living at a higher density than their savannah relatives and hence there would also be a selection pressure for increased tolerance of conspecifics. The result was a divergence into two populations - those more tolerant of living near people and with other cats living in close proximity to settlements, and those more reactive staying out on the savannah. Because of its importance in rodent control, the cat became an important religious object in ancient Egypt, and the speed of change from their ancestral species was probably enhanced through the keeping of large numbers of cats within temples that were isolated from interbreeding with wild cats. Since this time, the cat has largely fulfilled a function of vermin control, so there has been little control of reproductive activity with frequent matings between 'domestic' queens to feral or farm tom cats. This is in contrast to the dog, where diversification of use has led to huge variations in phenotype. Hence, the 'domestic short hair' cat of today has not only been domesticated for a much shorter period of time than the domestic dog, it has also been subjected to much less human selective pressure, leaving it behaviourally much more akin to its ancestral species than the domestic dog is to the grey wolf. Greater changes have taken place in the pedigree cat world, and changes here are, sadly, driven by fashions for physical appearances rather than behaviour or functionality. However, pedigree cats contribute only a small number to the overall cat population - there are currently over 7 million cats in the UK and only 10% are pedigree. Genetic differences within pedigree cat populations have led to different behavioural profiles between breeds and breed types, as well as different incidences of behaviour problems between breed types.

Feline Social Systems

The domestic cat has contradictorily been described as both a 'solitary' or 'independent' species, and a 'social' species in the literature. These different interpretations have arisen because in many ways the domestic cat retains characteristics of its solitary ancestral species, yet has also adapted to living in social groups within certain constraints. Like its ancestral species, the cat is a solitary hunter and still perceives the necessity to maintain a hunting territory - this is divorced from the fact that satiety is generally achieved from the bowls of food that we give our cats. In fact, maintaining a territory is such a strong evolutionarily important motivation for the cat that it leads to the presence of a range of different behaviour patterns in our domestic cats, from patrolling and chasing off other cats, to scent-marking behaviours. Olfactory signalling is an important behavioural strategy in a number of solitary species - as it enables individuals to leave 'messages' for others with the minimal necessity to come into direct conflict, to minimize the chance of injury. It is for this reason that olfactory communication is so important in the cat - it provides a signal that lasts over a period of time, and which gives a message to other cats remotely.

However, despite being solitary hunters, domestic cats have developed the ability to live in social groups, and in the right circumstances large numbers of cats can peacefully co-habit core territories. This characteristic probably developed due to the change in food availability around the time of domestication: the food resource became concentrated in small areas, requiring cats to live in close proximity to be able to take advantage. The focus of such social groups in feral situations is female cats and kittens. These groups are usually, but not exclusively, made up of related females, and kittens are often raised communally. Males tend to be on the periphery of such groups and often have territories large enough to overlap several groups of females. Within these groups, aggressive incidents are very infrequent and will tend to occur mainly when young cats, especially males, reaching social maturity are driven away from the colony. This is because the size of a colony of cats will not become larger than the availability of resources (food, toileting sites, nesting sites, etc.) allows. There is therefore no need for competition between cats within this situation, and hence they are able to live together without the necessity to show signals of appeasement, nor to have a hierarchical social structure. Members of a colony or social group show extensive affiliative behaviours towards each other, such as allorubbing and allogrooming. As well as reinforcing social bonds through tactile contact, these behaviours have the function of 'mixing' scent between individuals within a group. This creates a group 'scent profile' that enables cats to easily identify members of their social group. Where cats from outside a social group come into a group's territory area, high levels of aggression are shown, and the intruder chased away. As the group size is only large enough for the resource available, it is not adaptive for groups to allow others into their territory, as was the case for the individual ancestral wild cat.

'Social Stress' in Domestic Cats

Within the domestic environment, the restraints upon cats' ability to show social behaviour become more obvious. This is because cats within individual houses may be separate 'social groups' where neighbours' cats are seen as a threat. Often, even cats within a multi-cat household don't see each other as part of the same social group and largely occupy different 'core areas' within a house. This can lead to a high level of stress and conflict, particularly where owners put all the cats' necessary 'resources' such as food, water, litter trays, and entrance/exit points in the core area of one group, and others have to come into this area to get the things that they need. This type of conflict between cats is very common, and often cats go for long periods suffering high levels of stress. This can lead to a whole range of possible 'problem behaviours,' such as inappropriate toileting where cats cannot access a litter tray or exit point without having to pass one or more other cats; urine spraying to mark sites of particular conflict within territories; over-grooming in cats that do not show an active coping response to chronic stress; hiding away; inactivity; and active aggression and fighting between cats. Social stress from other cats can also be a factor in aggression towards people, either directly where owners carry the scent of other cats, or indirectly through the effect of chronic stress on the threshold for aggressive responses. In addition, chronic stress has been related to the development of disease states, such as feline interstitial cystitis: epidemiological studies have shown that living with another cat with which there is conflict is a significant risk factor for this condition. Having a large number of cats within a confined area, having a very unstable population of cats, or having insufficient access to resources for the number of cats in a household, are all common causes of individuals displaying some behavioural indicators of stress.

Obviously cats within a household can form very close social bonds with conspecifics. This happens most easily between litter-mates, or where unrelated kittens are raised together. As with feral cats, social cohesion is maintained through frequent rubbing sessions, which not only involves tactile communication but also involves the mixing and swopping of scent, such that all individuals in the group have a shared profile of scents. Conflict is most likely to occur where adult cats are introduced, particularly where a new adult is brought into a household with one or more existing cats. In these circumstances, the resident individual will see the new cat as an intruder onto their territory, and the new cat will be anxious about 'landing' in the middle of another cat's core area. Research has found that problems arising from the introduction of new cats into the household are the most common behavioural category for which cats are returned to rescue shelters after homing in the UK.

References

1.  Liberg O, Sandell M, Pontier D, Natoli E. Density, spatial organisation and reproductive tactics in the domestic cat and other felids. In: Turner DC, Bateson P, eds. The Domestic Cat: The Biology of Its Behaviour. 2nd ed. Cambridge, UK: Cambridge University Press; 2000.

2.  Kerby G, MacDonald DW. Cat society and the consequences of colony size. In: Turner DC, Bateson P, eds. The Domestic Cat: The Biology of Its Behaviour. Cambridge, UK: Cambridge University Press; 1988.