Common feline problem behaviors: Aggression in multi-cat households

Abstract

Practical relevance:

Being able to understand and intervene in cases of cat–cat aggression in multi-cat households is important for all veterinarians and behavior counsellors dealing with feline behavior cases.

Clincal challenges:

Feline conflicts are common, perhaps not helped by many owners’ assumption that this is the norm. Interventions can be complex in multi-cat households with large numbers of cats as there are more interactions to evaluate and monitor, and care needs to be taken not to negatively affect the other cats. There may be limitations due to the environment or the people involved and so behavior guidelines should always be tailored to the individual situation.

Aims:

This article reviews the main forms of aggression in multi-cat households and the appropriate behavioral interventions, considering both the typical scenarios and emotions/motivations most likely involved. It details essential environmental management for multi-cat homes, as well as an approach to friendly cat introductions.

Audience:

This article is aimed at veterinarians dealing with feline behavior cases as well as behavior counsellors, as both professionals are likely to experience cases of aggression in multi-cat households.

Evidence base:

The author draws on the published literature where available and, where there is a lack of research, on hypotheses derived from her own clinical behavior experience.

Introduction

Feline aggression in the form of both human-directed aggression and cat–cat conflicts is very common in the practice of veterinary behavioral medicine worldwide and is frequently cited by owners in their complaints about the behavior of their cats.^1-6 The focus of this article is conflicts between cats; owner-directed aggression is discussed in an accompanying article in this special issue.

Aggression is typified by a threat or injurious action directed towards another individual and can be demonstrated through specific vocalizations, body postures, facial expressions and characteristic attacks. Aggression is a common feline behavior, especially when cats are placed in a situation of proximity and non-affiliation. It can, however, also occur during exuberant play among affiliate pairs. In all of these situations, aggression appears to function as a legitimate part of feline communication. Aggressive behavior among cats is not, therefore, always a problem that requires intervention.

In terms of its prevalence, cat–cat aggression accounted for 25.7% of 70 behavioral cases seen by the author from 2007–2013 and 31% of cases in a 155-cat behavior series from 2008–2014, both in the Sao Paulo region of Brazil (unpublished data); in the latter, cat–cat aggression outnumbered house-soiling cases. In a study, also conducted in Brazil, feline aggression was the reason for 17.4% of owners visiting a non-specialist veterinarian; 21.7% of these cats were directing aggression towards animals including other cats in the household. ⁶ These results are consistent with feline caseloads described in other regions.^1-4 In all of these surveys, unacceptable elimination and aggression between cats were the most frequent problems reported, with cat–cat aggression exceeding unacceptable elimination in the study by Amat et al. ¹ Not only does cat–cat aggression appear to be over-represented in referral clinic populations, but the number of cats showing aggression to other household cats in the general pet population is also high. ⁷ Although still under-explored, the caseloads of several behavior experts suggest that the problem of feline aggression is increasing, perhaps not helped by the fact that many owners assume cat–cat aggression to be the norm.

Multi-cat households and the rise in cat–cat conflicts

The cat population is increasing worldwide, not only as a result of rising numbers of new cat owners, but also existing owners acquiring additional cats. ⁸ The density of cats in multi-cat homes is therefore also increasing, which is likely linked to the reported rise in cat–cat aggression. Figures, for example, from a well-established feline-only practice in Sao Paulo, Brazil showed that among the 585 cat owners visiting the clinic during a given month in 2016, 85% owned more than two cats and 50% owned more than five cats (A Reche-Junior, personal communication).

In countries such as the UK and France, the typical multi-cat household is characterized by a few individuals sharing an environment that generally includes access to the outdoors. This is in contrast to countries, such as Brazil, that have densely populated urban areas dominated by blocks of small flats, where the typical multi-cat household is composed of several individuals cohabiting an environment with no or limited outside access (eg, a balcony). Added to this is the fact that many people choose a new cat based on attributes other than behavior, such as appearance; alternatively there is no selection per se as they adopt one (or more) cats that have been found abandoned on the streets. Both of these factors contribute to making multi-cat groups highly heterogeneous.

Particularly when cats have been known to each other since a young age and the environment is appropriate, they can affiliate well in a multi-cat home, and, despite proximity, conflict levels can be kept low. However, in heterogeneous groups with too many cats in a restricted space lacking environmental adequacy, such as opportunities to escape and hide, high levels of conflict are likely to arise with serious problems for the cats and owners.

While undoubtedly life as a single cat is not free of distress, the limited space in multi-cat homes is an obvious challenge for cats, which lack social skills and preserve their privacy.^9-11 The behavioral flexibility that is typical of the feline species may contribute to cats’ ability to adapt and decrease their distress in multi-cat homes, but clearly this is not a general rule. Prevention of conflicts to improve the welfare of cats in multi-cat households is therefore a priority.

Aggression in multi-cat households: underlying mechanisms and common scenarios

Given that aggression is a behavioral sign and not a diagnosis per se, in order to deal appropriately with any cases of conflict among household cats the underlying mechanisms for the aggression must be identified. This can be undertaken by gathering an accurate history, which covers the main scenarios in which aggression occurs, as well as the body postures, facial expressions and vocalizations exhibited by the cats, triggers and targets, and owners’ attitudes. Rather than interpretations, we require owners’ observations to be able to infer the motivational-emotional systems of all the cats involved (see articles in Part 1 on understanding feline emotions and recognising and assessing feline emotions). These allow us to reach a specific behavioral diagnosis, and thus increase the chance of successful intervention.

One essential step while identifying underlying mechanisms in cases of cat–cat aggression is ruling out medical problems. Some diseases or conditions can lead to pain (eg, osteoarthritis), discomfort, decreased or increased metabolism (eg, hyperthyroidism) or disease-specific odors (eg, otitis, anal gland impaction), among other factors, affecting how a cat appears and/or behaves towards others in the group. Either the cat itself or the other cats may react aggressively. An initial physical examination is therefore essential.

Depending on what is detected during the examination, or any other clinical signs reported by the owner, ancillary tests including complete blood work, a biochemical profile, radiographs, ultrasound or even MRI and CT may be necessary. Cats older than 6–7 years that suddenly start to be aggressive should have a thyroid profile included in the medical investigation. For geriatric cats, tumors of the central nervous system or adrenal glands ¹² should be considered as possible underlying mechanisms.

Aggression between resident cats due to illness commonly presents as sudden mild to severe attacks without a previous history of conflict between the cats involved. Conflicts may wax and wane, following the course of the disease. The personality of the affected cat may suddenly change due to its physical state and, as a consequence, a more suspicious, curious or inquisitive approach by the others may lead to conflict. It is important to consider that the intensity of the attacks is not necessarily proportional to the severity of the medical condition. Furthermore, cats are not always clear in their physical signs, so in some cases trial therapy for the suspected condition and/or for alleviating its clinical signs is necessary to definitively exclude medical problems.

In addition to aggression between resident and neighbourhood cats (see box below), the key scenarios as far as multi-cat households are concerned are aggression between existing resident cats and aggression between resident cats and new arrivals.^1,2

Aggression between resident cats

Two forms of inter-cat aggression between resident cats are recognised: (1) ‘play aggression’ and (2) ‘non-play aggression’ (either directed or redirected). While in play aggression there is commonly a friendly approach (at least on the part of the aggressor), in non-play aggression there is typically a hostile approach.

Different emotional systems are likely involved in these two forms of cat–cat aggression. Cats show predatory sequences during play with others, and thus both ‘SEEKING’ and ‘PLAY’ emotional systems ¹⁶ are likely activated during play aggression between resident cats. ‘RAGE’ and ‘FEAR’ emotional systems ¹⁶ are more likely during non-play aggression. (For further discussion on emotional motivations, see the article in Part 1 on understanding feline emotions.)

Play aggression

During play aggression typical predatory–play behaviors occur but, in their enthusiasm, cats show real aggressive movements and lack inhibition in their scratching and biting. Typical interactive feline play is displayed by affiliated individuals and includes eye stare, stalk, chase, pounce, grab and bite (sometimes also wrestling and kicking with hindlimbs); vocalizations such as growling, hissing and screaming are generally absent, whereas short meows and chirruping sounds can be present. While playing is an indicator of good welfare in multi-cat households, when cats are extreme in their behavior during play, frustration, fear and even injury to other cats may occur. One common scenario is the aggressor cat being scolded by either the other cat(s) or the owner, leading to this cat feeling frustration or fear/anxiety; an expected consequence is then non-play aggression directed towards the other cat(s) or the owner.

Non-play aggression

Non-play aggression is manifested as either defensive or offensive displays towards the opponent by cats feeling fear, anxiety, frustration or other negative emotions. Defensive aggression is shown by a cat positioning itself in a protective manner (ie, crouching, turning away from the target, flattened ears, raised hackles, tucked head) and is commonly accompanied by growls and hisses. Offensive aggression is characterized by long meows and growls and the cat positioning itself in a more intimidating posture (ie, stiffened legs, hackles raised, staring and moving towards the target, stiff tail). For instance, two non-affiliate cats living in the same household may tolerate each other on most occasions, but when face-to-face encounters occur, aggression arises in either its defensive or offensive form from one or both cats.

The motivations for non-play aggression between resident cats vary (territorial defense, self-defense, resource guarding, etc), as do the underlying emotions. A typical scenario of non-play aggression in multi-cat homes is when cats are in close proximity to resources (eg, food, toys, bed, the owner) or encounter each other in a specific part of the territory (eg, a cat enters the bedroom and the other is there ready to attack). Some cats, either when near these resources/ areas or when perceiving other cats approaching them, may block the others’ access or threaten them with offensive aggression. Another scenario, which is common in small multi-cat homes, is where non-affiliate cats are prone to encounter each other in spaces that lack escape routes and/or hiding places, thus leading to defensive and/or offensive displays that can easily escalate to fights. The motivation(s) in these contexts can vary, thus making it very difficult to specify the motivational-emotional systems involved, but broadly speaking these cats are likely to be experiencing negative emotions.

Any other circumstance triggering distress (either acute or chronic), such as high population density or cats frequently coming in and out of the house (eg, owners fostering cats in their multi-cat homes), is likely to trigger non-play aggression by the resident cats due to the intensifying of their underlying emotions.

In the case of ‘despotic’ cats within a multi-cat group, offensive displays directed towards several cats irrespective of the circumstance are very common. By contrast, ‘pariah’-type cats will feel threatened by others regardless of their posture or the context; by frequently exhibiting defensive aggression, these cats thus trigger offensive aggression in others (Figure 1). In large multi-cat groups living in environments lacking outdoor access, frequent encounters among resident cats and restricted access to, and competition for, resources are common, contributing to frequent displays of non-play aggression between resident cats.

Figure 1.

(a-d) The tabby-and-white cat in this sequence of images is displaying defensive aggression, while the black cat displays offensive aggression

A particularly concerning scenario is the redirected form of non-play aggression that occurs commonly in multi-cat households (see box).

Aggression between resident cats and new arrivals

cat–cat aggression when new cats are introduced is very common in multi-cat households. Unfortunately, many owners wrongly assume that cats, like humans, will be pleased to receive a new member in the group and get very frustrated when aggression occurs. Cats, however, are quite unique in their social behavior,^17,18 and are more likely to get on well with others when well socialized at an early age (2–9 weeks old), when environmental conditions allow and when they have been known to each other since a young age. Kittens arriving in a feline group are more likely to be well tolerated by the adults. Under any other circumstances, aggression should always be expected with new arrivals and therefore prevented.

Whether aggression involving new arrivals is due to lack of familiarity, unfamiliar sounds and smells in the group, perceived threat over resources, redefinition of environmental occupation and marking, decreased available space, or a combination of these factors, is not known. While this aggression mostly occurs from the resident cats towards the new arrival, sometimes it is initiated by the latter. In a survey conducted by Levine et al, ¹⁹ owners commonly reported fighting when a new cat arrived, and in half of these cases the cats were introduced by simply putting them together immediately. Perhaps unsurprisingly, owners who reported current fighting among their cats witnessed aggressive behaviors during the cats’ first meeting and perceived this first encounter as not friendly. ¹⁹

Initial fights between resident cats and new arrivals can be severe to the point of resulting in injury to the cats (sometimes also to people) and leading to the owner confining or even abandoning the new cat. On other occasions attacks are moderate and the victim (resident or new cat) keeps itself hidden most of the time. As a consequence, other problems may occur, such as house-soiling and/or diseases or behaviors related to chronic distress (eg, cystitis, excessive self-licking).

Aggression between resident cats and new arrivals can sometimes decrease naturally over time. In other instances, owners report waiting months (or even years) for the conflict to stop, but this never happens. While in many cases acceptance of new arrivals is just a question of time (given appropriate and monitored introductions), in other cases, success, defined as the cats sharing the same evironment without fighting, may not be achievable and rehoming should be recommended (see later). Research looking at which cases are more likely to be successful is necessary.

Aggression in multi-cat households: managing problems

Aggression between resident cats

Play aggression

Increasing play opportunities is essential. One recommendation is providing cognitive environmental enrichment in the form of positive and predictable ‘play time’ with the whole group. During these sessions, several small toys are scattered around the room for the group to interact with, while more energetic play with special items, such as a cat wand or automatic toys, can be directed towards the aggressor. A short time each day separated from the group in an enriched room may be beneficial for alleviating play motivation by the aggressor, thus decreasing aggressive play towards the other cats.

Non-play aggression (directed)

Managing the environment is crucial (see article in Part 2 on environmental and behavioural modification). To decrease encounters and competition around resources, while also increasing safe places, the environment must fit a multi-cat group (as discussed later in the section on ‘Transforming multi-cat households into feline territories’). Persistent attempts by despotic cats to threaten others can be managed by fitting a small cat bell collar; this will add a sense of control for the other cats, as they will be able to anticipate when the aggressor is approaching, thus giving them time to escape.

Separating the despotic cat from the group for a short amount of time in an enriched room every day, accompanied only by cats that it gets on well with, may be beneficial in alleviating offensive aggression. Similarly for pariah cats, a regular amount of time spent separated from the group in a preferred room with the owner (eg, night time in the owner’s bedroom), and again accompanied only by cats that they get on well with, may be helpful in alleviating fear and defensive aggression by pariah cats.

Environmental management, as described in ‘Transforming multi-cat households into feline territories’, as well as in the form of specific routines, including ‘play time’ and ‘treat time’, is important in helping to desensitize and countercondition the cats to each other (see article in Part 2 on environmental and behavioural modification). For cases involving very frequent (eg, daily) and severe (eg, injurious) attacks, either because the aggressor has a very impulsive character, the victim has a very fearful character or the hostility between the cats is high, separation for days or weeks, followed by careful reintro-duction as if the cats were new to each other (see later), is recommended.

Non-play aggression (redirected)

Separation of the cats for a few hours or days, followed by careful reintroduction while desensitizing and counterconditioning the aggressor to the eliciting stimulus, is required in the case of redirected non-play aggression. For instance, where there is an eliciting noise, having play and/or treat time while the noise is presented (initially at a low volume and gradually increasing to full volume while the cat is relaxed) will help the cat to become accustomed to it, and thus decrease the risk of the cat redirecting aggression again in future encounters. Any other eliciting stimuli, such as smells, should be presented in the same manner to desensitize and countercon-dition the aggressor.

If the stimulus is identified but cannot be controlled (eg, a neighbourhood cat cannot be presented gradually for desensitizing and counterconditioning purposes), the resident cats should not be exposed to it. As discussed earlier, identifying when neighbourhood cats are around is crucial to guarantee that resident cats are kept inside the home at these times.

Aggression between resident cats and new arrivals

Separation of cats in order to restart the process of appropriate friendly cat introductions, as discussed in the next section, is recommended in cases where the new arrival was abruptly added to the group. Where a friendly introduction process was commenced but failed, likely because it was carried out too quickly and/or in an incorrect manner, it may be restarted from the point immediately before the cats or owner(s) struggled. In some cases, this will mean going back to the initial steps where the cats are kept permanently separated except for during the behavior sessions.

Friendly cat introductions: essential for preventing conflict and restoring group harmony

Key to preventing aggression in multi-cat households is the appropriate introduction of any new cat arriving in the group. A step-by-step program for friendly cat introductions for new arrivals is described in the box below. ²¹ Such a process is also considered a tool for treating cat–cat aggression, since, as discussed earlier, behavior intervention will sometimes require separating resident cats that are fighting and then reintroducing them as if they were new to each other.

Figure 2.

Friendly cat introduction – step 1. (a) Appropriate environment for a new arrival. (b) Special food being provided to the resident next to the door to the new arrival’s room

Figure 3.

Friendly cat introduction – step 3. Visual contact sessions being provided: (a) with one of the cats in a cat carrier and using special food as a reward; and (b) with one of the cats in a cat bag and using petting as a reward. Note that cats must first be given the opportunity to become familiar with cat bags using positive associations

Figure 4.

Friendly cat introduction – step 4. Cats interacting with a selection of toys and items (a,b) and eating special treats (c) during a supervised session of physical access

Figure 5.

Friendly cat introduction – step 4. The aggressor wearing a harness without a leash

Transforming multi-cat households into feline territories

Another key element in preventing aggression in multi-cat households is environmental modification. This is also important when treating cat–cat aggression as behavioral intervention for such cases will, with rare exceptions, require strategies aimed at promoting feline dispersal, decreasing competition for resources and increasing feline self-confidence through environmental control.

The environmental modification program for multi-cat households used by the author and colleagues is referred to as ‘transforming multi-cat households into feline territories’. Central to the program is deciding on the amount and location of all of the feline resources (food and water bowls, beds, scratching posts, etc); this is based on what is most appropriate for the cats, given their nature and their physical and emotional needs when living in a group, often in a restricted space. Among other things, the program emphasizes the concept of multiplying resources and the provision of safe places, as proposed in the AAFP and ISFM Feline Environmental Needs Guidelines. ¹¹

The program has been extensively applied by the author in Brazil, both during behavioral consultations in multi-cat households and during behavior workshops for cat owners, veterinary students and cat professionals in general. During these workshops, the program is presented as a dynamic activity in which the participants work towards building feline territories within different household set-ups. They are provided with high-scale drawings of household plans and a history of the multi-cat group that lives there, and are asked to add resources as appropriate.

Application of the program requires the following five steps:

1. Identifying affiliative and agonistic interactions displayed by the resident cats, thus detecting subgroupings if they exist, as well as overtly aggressive and/or submissive individuals. (See box on ‘Identifying and monitoring social relationships’ on page 226.)

2. Getting to know the configuration of the house (measurements, furniture, uses, entrances, exits, etc) and all the places available to the cats, as well as forbidden areas, and how the resident cats typically occupy it.

3. Recognizing all of the problem behaviors present in order to maximize the impact of the program; thus as well as helping to prevent/manage multi-cat aggression, other behavioral issues that are very common in multi-cat households, such as house-soiling and destructive scratching, are also addressed.

4. Taking into consideration owner adaptability and limitations, both in terms of the funds available to buy new items and flexibility to make changes within the home. The rule is to avoid extremes such as requiring the owner to change everything (which may, in fact, be detrimental to the cats if done all at once) or accepting an owner’s refusal to make any change at all.

5. Applying the principles of multiplying, decentralizing and sectorizing resources whenever possible.

In practical terms the program begins with a detailed interview with the owner and a careful tour of the house. Steps 1–4 are then performed, following which an environmental modification plan is developed based on step 5. Owners must be advised that changes should be applied gradually supported by behavioral monitoring. Good practice for owners acquiring a cat for either starting or increasing a multi-cat group is adapting the environment before any problems arise. In essence, this means ‘transforming households into feline territories’ during the process of introducing the new cat into the group as explained earlier. The ‘Case notes’ on pages 231 and 232 illustrate how the principles are applied.

Figure 6.

Environmental modification for multi-cat household 1 – a 60 m² flat with three affiliated cats, two of which were exhibiting play aggression

Figure 7.

Environmental modification plan for multi-cat household 2 – a 60 m² flat with two cats exhibiting non-play aggression

Summary of approaches

Due to many reasons already discussed in this article, such as the risk of injuries to both cats and humans and the often time-consuming nature of the treatment plans, cases of aggression between cats in multi-cat homes are often the most challenging.

Overall, play aggression is mainly treated with appropriate and structured play sessions provided and monitored by the owners. For non-play aggression, in mild cases in which aggressive displays are neither severe nor frequent, the main focus is on environmental modification (transforming multi-cat households into feline territories), and the cats can be kept together. In moderate to severe cases, in which fights are very frequent, the best option is to separate and reintroduce the cats. In the most severe cases of non-play aggression, reintroduction will rely on a very gradual, long-term step-by-step friendly cat introduction process, with the help of psy-choative medications, as well as lots of patience and various adaptations to the home.

Rehoming and permanent separation

Even following these steps, there are no guarantees of success. In addition, not all owners are willing to implement or are capable of implementing all that is needed for restoring the harmony in a multi-cat home with severe conflicts. In these instances rehoming, as well as permanent separation of the aggressor and victim (with both accompanied by their affiliative individuals whenever possible – ie, fragmenting the multi-cat group into permanent feline subgroups), are viable alternative options.

Key Points

• Behavior initiatives to both treat and prevent cat–cat aggression problems are essential to safeguard feline welfare in multi-cat households, while also helping to avoid commonly associated negative outcomes in untreated cases, such as feline relinquishment and euthanasia.

• Although overall recommendations still lack scientific validation, the key principles for preventing cat–cat aggression in multi-cat settings are keeping the cat density low, enriching the environment and, in the case of new arrivals, introducing cats in a feline-friendly fashion.

• In cases where there is an existing problem of cat–cat aggression, scenarios must be carefully scrutinized to help inferences to be made about the emotions and motivations of the individuals involved.

• Treatment involving behavioral and environmental modification (including pheromone use), as well as medication when necessary, should be based on the individual scenario, the emotions/motivations involved, severity of aggression and owner skills.

• In some instances rehoming or permanently separating the cats are viable options.

• Scientific studies focused on the behavior and welfare of aggressive cats in multi-cat households are needed. The knowledge generated should be shared with multi-cat owners, thus assisting them to better observe and interpret their cats’ behavior. This will help in resolving and preventing problems, while also improving feline welfare through very specific and science-based initiatives.