Aggression and Aggressive Behaviour in Cats
Of the various behavioural problems encountered in cats, aggression is probably one of the greatest challenges, not only in breeding households but also in homes shared by more than one cat. A breeding household can grow very quickly from a single cat to several, and sometimes even a dozen or more — and here I am referring only to adult cats. Once kittens arrive, the population density increases still further. The "ordinary" cat caregiver, meanwhile, often becomes so fascinated by their first feline companion that sooner or later they decide to welcome a second cat into the home, and quite frequently a third. Given that cats are not obligately social, group-living animals in the same sense as many other social species, such living arrangements can sometimes contribute to tension and conflict. Fortunately, this is by no means inevitable. Nevertheless, introducing a new cat into an existing group can be difficult, and in some cases the situation becomes overwhelming for caregivers who were simply not prepared for such a scenario.
It is essential to distinguish aggressive behaviour from behaviour associated with elements of the predatory sequence. The two are very often treated as equivalent, yet differentiating aggression from predatory or play-related behaviour is crucial when deciding how the problem should be managed. A cat that grabs our feet or "attacks" a child running past is not necessarily aggressive. The cat may simply have an insufficiently fulfilled need for movement, play and predatory activity. Providing an appropriate amount of interactive predatory play, incorporating the relevant elements of the predatory sequence — stalking =>> visual orientation and tracking =>> pursuit =>> capture and biting — will often significantly reduce or resolve the problem. Such behaviour may certainly be troublesome from the caregiver's perspective, but it should not automatically be classified as aggression. Similarly, apparent "aggressive attacks" during play, when an aroused cat grabs and attempts to bite a human hand, may represent further elements of predatory or play behaviour rather than aggression. In such cases, play needs to be modified appropriately so that the cat can complete the activity in a satisfying manner without the caregiver being injured in the process. Following a sufficiently complete bout of predatory play, the cat will often eat, groom and then rest or sleep. We do not observe this same behavioural sequence in cases of genuine aggression.
Aggressive behaviour can take many different forms. It may range from subtle, passive forms of social pressure, such as prolonged staring at another cat, through physically blocking access to important resources such as food or litter trays, to more or less overt threat displays and, ultimately, direct attacks and fights. Fights between cats can be extremely serious and may result in physical injury. An even more significant consequence, however, is that cats may begin living in a persistent state of fear, vigilance and perceived threat. This affects not only the cats directly involved in the conflict. Other cats observing repeated confrontations may also feel insecure and unable to relax — after all, from their perspective, there is no certainty about who may become involved next. One aspect of intercat aggression that I believe is frequently underestimated is its effect on kittens developing within such an environment. Young cats may learn maladaptive responses and develop fear of other cats through repeated exposure to threatening social interactions. Such kittens are often more difficult to introduce successfully into new homes where another cat is already present.
Aggression can therefore take many forms, and fighting is not the only manifestation of aggressive behaviour. Aggression may be active or passive. Passive forms are very frequently overlooked, not only by breeders but also by caregivers living with more than one cat. Passive aggression or social intimidation may involve staring at another cat in a way that prevents it from approaching food or a litter tray, or physically positioning the body so as to block access to an important resource. There may be no vocalisation, no direct attack, no hissing and no growling. Nevertheless, a cat repeatedly exposed to this form of social pressure may become unable to function freely in the presence of the other individual. It may stop using a favourite resting place or avoid approaching food whenever the other cat is nearby.
Passive aggression and resource blocking should never be dismissed simply because the cats are not physically fighting. The consequences can be serious and very tangible. A targeted cat may, for example, be prevented from accessing a litter tray. The other cat may simply lie in the route leading to the tray, making it impossible or emotionally difficult for that particular individual to approach and enter. The same may occur around food bowls or preferred resting sites. A cat subjected to persistent passive aggression or social intimidation may gradually withdraw from normal activity. Exposed to chronic tension and persistent social stress, the cat may become apathetic and effectively "disappear" from everyday household life.
Apathy and withdrawal are frequently underestimated problems. This is partly because an apathetic cat causes virtually no difficulty for the caregiver. The cat may appear to be an ideal member of the group: it does not play, but neither does it become involved in fights or conflicts, and it does not display overt aggression. Such a cat often has a deeply concealed "private place", hidden from the rest of the household. It eats when the other cats are not nearby and does everything possible to remain "invisible". Unfortunately, persistent stress and behavioural withdrawal may be associated with significant effects on physical health. A cat may subsequently be found to have various medical problems, sometimes identified incidentally during routine veterinary examinations. Chronic stress is recognised as an important contributing or exacerbating factor in a number of feline disorders, particularly some lower urinary tract conditions, and may also influence metabolic health. A frustrated or chronically stressed cat may additionally begin to display stereotypic behaviour, such as fabric sucking, or compulsive-like behaviour, including excessive grooming that may result in extensive areas of alopecia, particularly on the abdomen and hind limbs.
Active aggression encompasses a very broad range of behaviour, beginning with threat postures and piloerection, progressing through hissing and growling and, in more extreme cases, culminating in attacks involving the paws, extended claws and even biting. Overt attacks may sometimes appear highly strategic. The aggressing cat may wait patiently near critical access points, such as the exit from a litter tray or a route leading to water, and attack another cat when that individual is least prepared to defend itself or escape. Such attacks may become repetitive and systematic, eventually creating a situation in which the targeted cat lives in a state of persistent stress and adopts a pattern of profound withdrawal from normal daily activity, with all the potential consequences described above.
Aggressive behaviour can be divided into several categories according to its underlying motivation or trigger, and the way in which it is expressed may also vary considerably.
Territorial Aggression
Although our cats may have constant access to food and water and face no obvious threat to their survival, behavioural mechanisms associated with controlling and maintaining access to important areas and resources remain deeply embedded in the feline behavioural repertoire. Cats monitor and may defend areas that they perceive as important. For a domestic cat, this may include the accessible areas of a flat or house and, in the case of a home with a garden to which the cat has access, the outdoor area as well.
Within this environment, a cat will often have particular strategically important locations — preferred areas that function as highly valued personal space. If another cat develops a preference for precisely the same strategic location, its presence may be perceived as an intrusion. The development of such individually preferred areas can occur even between cats that previously appeared to have an affiliative relationship. In breeding households, changes in tolerance between females may also be associated with stages of the oestrous cycle. Females approaching oestrus may persistently attempt to drive perceived "rivals" away, although this is certainly not inevitable. I have also repeatedly observed synchronisation of oestrous cycles and females apparently experiencing their shared "misfortune" together when there was no male available to provide consolation.
In territorial aggression, there is usually a clearly expressed but relatively brief threat phase, often accompanied by hissing or even growling. This may be followed by a rapid chase intended to drive the "intruder" away. In milder cases, the pursuit stops as soon as the other cat leaves the area considered particularly important — a favourite shelf, resting site or position on a cat tree. In these situations, helping the cats is often relatively straightforward.
The prognosis is less favourable when a cat displaying territorial aggression appears to claim virtually the entire available environment and is unable to tolerate the presence of another cat anywhere within it. Such cases are relatively uncommon, but they do occur. In these cats, the attack does not stop when the other individual retreats. Instead, the pursuit continues. The targeted cat may be chased until it is cornered and, unless the caregiver intervenes, may be subjected to a serious physical attack involving teeth and claws.
Personally, I find it extremely difficult to see how a cat with such an intense and pervasive need to control the entire available space can safely and comfortably remain within a multi-cat group. I also believe that severe, persistent and generalised aggression of this nature should be taken very seriously when making breeding decisions. This is important not only because of the difficulty of maintaining adequate welfare within the group, but also because temperament and behavioural predispositions may have a heritable component. In a non-breeding household, caregivers may ultimately need to accept that their cat is not an individual capable of comfortably sharing its living environment with another cat.
It is useful to analyse the cat's broader relationship with its environment and with the people around it, as well as its responses to visitors, unfamiliar situations and environmental change. These observations may provide valuable information and help us anticipate potential difficulties.
A particular form of territorial or social aggression is commonly referred to as non-recognition aggression. This involves aggressive behaviour directed towards a familiar member of the social group — sometimes even a cat with whom the individual previously had a close affiliative relationship — who, for some reason, is temporarily perceived as unfamiliar. I frequently observe this after a cat returns from a veterinary clinic. It is less likely following a brief visit for routine vaccination, when exposure to unfamiliar odours is relatively short, but may occur after surgical procedures such as neutering, following a cat show or after a breeding cat returns from another cattery after mating.
This type of aggression is not usually among the most severe. In many cases, it is limited to hissing, general confusion and overt avoidance or hostility. Direct physical attacks are less common, and the problem frequently resolves within approximately 24 hours, or at most a couple of days.
Redirected Aggression
Redirected aggression frequently occurs when a cat cannot direct its response towards the actual source of arousal or perceived threat — for example, an unfamiliar cat walking past a window. The potential opponent is inaccessible. The resident cat may therefore enter a state of intense arousal and display threat behaviour towards the visible but unreachable stimulus. If the situation remains unresolved, the aggressive response may subsequently be redirected towards another cat that happens to be within reach. In this type of aggression, we will often observe an initial phase of threat behaviour directed towards the stimulus that the cat can see but cannot access, followed by an attack on an available nearby individual.
Another example of redirected aggression is aggression associated with frustration. This may occur when Cat A, having been driven away by Cat B, subsequently directs its frustration towards Cat C — particularly if Cat C is already fearful of Cat A. I have frequently observed this type of behaviour at cat shows. A cat may have just been groomed rather roughly by its caregiver while being firmly restrained and, once returned to the show cage, immediately direct its arousal and frustration towards a feline companion.
The target of frustration-related redirected aggression may be another cat, but it may also be another animal or a human being, including the cat's own caregiver. In these situations, there may be little or no observable threat phase before the attack. The higher the level of arousal and frustration, the shorter the warning phase may become. In extreme cases, there may appear to be no warning at all and the attack occurs suddenly.
The chain of redirected aggressive behaviour does not necessarily involve cats alone. It may be linked to interactions throughout the entire social environment in which the cat lives — between the cat and other cats, other animal species and human members of the household. Distressing interactions between caregivers, including shouting and arguments, may contribute to fear and frustration in a child. The child may then shout at the cat, and the cat, in turn, may redirect its own heightened arousal towards another cat or another member of the household. Emotional and behavioural responses can therefore spread through a household in complex and sometimes unexpected ways.
Nevertheless, in my experience, the most frequent sources of feline frustration in multi-cat homes involve other cats and the organisation of the environment: insufficient access to locations perceived by the cat as safe, too few attractive resting areas and an inadequate use of vertical space.
Frustration-related redirected aggression is probably one of the most common forms encountered in our homes. Despite this, a cat displaying aggressive behaviour is often very quickly labelled "dominant" or "territorial". Such labels oversimplify feline social relationships. Cats living in groups do not necessarily organise themselves according to a simple linear dominance hierarchy. It is more useful to examine specific relationships between individual cats and to consider those relationships in the context of particular resources. The relationship between Cats A and B around a food bowl may look entirely different from their relationship around a highly valued resting site. Determining whether redirected aggression is involved is therefore crucial when attempting to identify an effective solution to the problem.
Fear-Related Aggression
Fear-related aggression is the type of behaviour displayed by a cat that feels cornered and no longer perceives escape as possible. From the cat's perspective, it may be fighting for its life. This is an "all or nothing" response. What distinguishes this form of aggression from those described above is that aggression represents the final rather than the initial element of the cat's response to a threatening situation. This certainly does not mean that fear-related aggression is less dangerous. Quite the opposite.
The cat will initially attempt to escape. When escape is no longer possible, it may attempt to increase distance through threat displays: piloerection, defensive posturing and hissing. If these signals fail to remove the perceived threat, the cat may begin to fight with extraordinary intensity, investing virtually all of its available energy in the response. At this stage, the cat's capacity to process the situation and flexibly adjust its behaviour may be severely compromised. It may be unable to assess how much force is required to remove the threat and may even fail to respond immediately when the original danger has passed.
A cat in this state can be extremely dangerous. The presence of a caregiver speaking in a soothing voice does not necessarily alter the situation. Attempting to approach, touch or actively "calm" the cat may further increase its fear and arousal. The safest approach is generally to reduce stimulation, maintain distance and allow the cat sufficient time and space to recover and return to a state in which it can once again assess its environment more appropriately.
An observant caregiver will usually learn which situations trigger such an intense fear response in their cat. These triggers should, wherever possible, be avoided or carefully managed. The cat's individual fear threshold — the point beyond which behavioural control deteriorates and an intense defensive response occurs — varies considerably between individuals. In some cats, panic may be triggered by unfamiliar sounds or strangers entering the home. In others, even relatively routine husbandry procedures requiring restraint may provoke an extreme response.
Understanding our cat's individual strengths, vulnerabilities and triggers is essential when developing a management strategy intended to eliminate, or at least substantially reduce, exposure to situations that provoke intense fear.
Managing Aggressive Behaviour
When aggressive behaviour occurs, the first step is to identify its likely underlying motivation and context. Are we dealing with territorial aggression, redirected aggression or fear-related aggression? In cats that have known one another for a long time and previously maintained a stable, affiliative relationship, fear-related aggression directed specifically towards the familiar companion may be less likely as the primary explanation, although the complete behavioural and medical context must always be considered.
When a familiar companion is temporarily "not recognised" after a prolonged stay at a veterinary clinic or following a medical procedure, changes in the cat's normal scent profile may contribute to non-recognition aggression. If we are introducing a new cat, territorial and resource-related responses must certainly be considered. However, we need to avoid oversimplification. Territorial aggression in this context would primarily describe attacks directed towards the newcomer. Aggressive behaviour may also appear between existing resident cats. In such cases, redirected aggression associated with frustration or heightened arousal may be involved.
It is extremely important to identify cats that cope particularly poorly with the introduction of new individuals and to provide them with appropriate support in managing fear, uncertainty and negative emotional arousal. Sometimes the addition of an enclosed resting area or a high shelf from which the resident cat can safely observe the newcomer can make an enormous difference.
Redirected aggression can often be suspected — or made less likely — through careful observation of the events immediately preceding an aggressive incident. When redirected aggression is involved, we should attempt to identify and, wherever possible, remove or manage the original trigger. If a neighbour's cat walks past the window every day and repeatedly provokes intense arousal and aggressive incidents in the resident cat, it may be appropriate to obscure the relevant part of the window and prevent visual contact between the cats.
The same general principle applies to fear-related aggression. If another cat within the group is the source of intense fear, the cats may need to be separated and their relationship carefully assessed. If a cat responds to visitors with panic, it should not be forced to interact with unfamiliar people. If a particular cat is severely distressed by a female caring for newborn kittens, it should not be housed in close proximity to the queen and her litter during the postpartum and nursing period. If a cat redirects aggression arising from frustration, identifying the source of that frustration is fundamental.
In cases of territorial aggression, an initial period of separation may be necessary. The environment should provide multiple, spatially separated feeding stations, scratching structures and resting sites. Territorial conflict is particularly common during unsuccessful attempts to introduce a new cat into an established group. Cats should never simply be left to "sort it out between themselves". Repeated fights may strengthen negative associations and contribute to an escalation of aggressive behaviour. Eventually, the relationship may deteriorate to a point at which successful reintroduction becomes extremely difficult or impossible.
Furthermore, living in a state of persistent tension and anticipating an attack may contribute to additional behavioural problems, including elimination outside the litter tray. When problematic behaviour first becomes apparent, the cats should initially be separated. Ideally, controlled exposure should allow them to see and smell one another through a secure barrier, such as a door opened only slightly, a mesh barrier or a glass partition, depending on the individual cats and the intensity of their responses.
If the cats do not attempt to attack one another under these controlled conditions, the prognosis may be relatively favourable. They can, for example, be fed on opposite sides of the barrier at a distance at which both remain comfortable, allowing visual and/or olfactory contact while creating opportunities for neutral or positive experiences in one another's presence. In my experience, when cats continue to launch persistent attacks at one another even through a secure barrier, the prognosis for comfortable cohabitation within the same social group is considerably more guarded.
After a period of successful coexistence with controlled, limited contact, gradual reintroduction may be attempted. However, certain environmental principles must be observed. The available space should contain several feeding locations and multiple litter trays, together with numerous resting sites, hiding places and elevated shelves or enclosed resting areas. Elevated locations are particularly important. If we choose to live with more than one cat, we need to accept that additional climbing and resting resources will usually be required.
This does not necessarily mean purchasing another expensive piece of cat furniture. What matters is height, a comfortable resting surface that also provides a useful observation point, and safe escape routes. Ideally, every important elevated resting location should offer more than one route of approach and departure. A shelf can therefore be an excellent resource, but it should be integrated into the room in such a way that a cat resting there is not trapped if another cat jumps onto the same structure. In other words, the shelf should form part of a connected route — for example, from a cat tree to a shelf, from the shelf to a sofa or bed, and from there to a chest of drawers or another elevated surface.
If cats are capable of tolerating one another, they may be able to share the same general living environment provided that they are not forced into persistent competition for highly valued resources. An insufficient number of hiding places and strategically important resources — particularly comfortable elevated resting and observation sites — is, in my opinion, one of the most common environmental problems in homes shared by more than one cat. I discuss the organisation of a feline-friendly environment in greater detail in the Cat-friendly Home section.
In particularly difficult cases, veterinary surgeons may prescribe anxiolytic or other behaviour-modifying medication. Medication should not, however, be regarded simply as a way of suppressing visible behaviour while leaving the underlying problem unchanged. Depending on the individual case, appropriately selected pharmacological support may form part of a broader behavioural treatment plan, particularly when anxiety, fear or other clinically significant emotional states are involved. It should be used under veterinary supervision and combined, where appropriate, with environmental modification and behavioural intervention.
Synthetic feline pheromone products may also be useful as an adjunct in some cases involving territorial insecurity or intercat tension. These products are intended to provide olfactory signals associated with environmental familiarity and security. Pheromone products have become extremely popular in recent years and, unfortunately, are sometimes treated as a universal solution to every feline behavioural problem. They may be helpful when a cat's stress is associated with environmental uncertainty or changes in perceived territory, but they are not a treatment in themselves. They cannot replace careful environmental assessment, appropriate resource provision, gradual behavioural work and the slow process of helping cats adjust to a new situation and, where possible, to a new feline housemate.
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Dorota Szadurska, COAPE Behaviourist Supervisor
Graduate in Advanced Diploma in Feline Behaviour Management (Level 5, UK)
Member of The International Society of Animal Professionals
Member of The International Association of Animal Behavior Consultants