Cat faeces 'logs' in litter tray block another cat's toileting routine

This is a cross-post as I think it is an interesting topic for cat caregivers.

As a cat caregiver you must have heard about the need to keep the litter tray clean. This applies particularly in homes where there are several cats. And in those homes if cats are sharing a litter tray or there are less litter trays than cats and one cat has used the litter tray, the next cat will be put off by the sight of faeces logs in the litter substrate but not by the smell of the logs.

This image summarises the study findings. Image: MikeB. Words: the study.

And in being put off by the sight of the faeces they may not use the litter tray and may even defecate outside the litter tray (inappropriate elimination).

The interesting aspect of the study which discovered this (see citation below) is that the problem for cats sharing litter trays is the physical presence of the faeces in the substrate not the odour of the other cat's faeces. 

This surprised me as cats have very effective noses and they scent mark with urine and faeces. Because scent marking is so big in their lives you'd have thought that the odour of another cat's faeces would be the off-putting issue but no.

This is about VISUALLY offending the cat about to embark on a toilet session and not in terms of odour.

The study worked with cats that got along. It might be a different story if they did not. They discovered this phenomenon by depositing false cat faeces in the litter tray that were odourless. The cats were put off by them. 

They also put in 'faux-urine' and they were put off by that as well, even more so.

Citation for the study: Does previous use affect litter box appeal in multi-cat households? Researchers: J.J. Ellis, R.T.S. McGowan, F. Martin. Link: https://doi.org/10.1016/j.beproc.2017.02.008

P.S. It is best not to super-clean litter trays and remove all the natural feline scent from it as cats are attracted to the scent of their poop and pee and use the area as a toilet.

P.S. 2 - The best practice in multi-cat homes is to have one tray per cat. This would avoid the above mentioned issue. I suspect that not many owners of several cats do this however. The issue mentioned on this page may be a big factor in trying to control cat toileting in multi-cat homes.

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P.S. please forgive the occasional typo. These articles are written at breakneck speed using Dragon Dictate. I have to prepare them in around 20 mins.

Lodger shoots home owner 10 times arguing over 6 cats

FORT MYERS, FLORIDA, USA - NEWS AND OPINION: I'll keep this concise and short. A woman allowed a man who had been evicted from his previous residence to become a lodger at her bungalow with his three cats. A kindly act which turned very nasty.

The home where it happened. Image: Google Maps.

The man, 59-year-old Glenn White, started to acquire cats more cats. We are not told how but they were probably rescue cats. He brought three more cats into the home.

The woman found this to be too much and asked that the cats live outside.

“The victim and White have been arguing for the past couple of days about the cats and how the victim would like the cats to live outside the house instead of inside the house. On (March 8), the victim got tired of having all the cats inside the residence and told White she was going to place them outside in the lanai.” - Police report

A 'lanai' is a Hawaiian term for a porch.

Mr White became upset and arrived with a gun - Smith & Wesson SD40 - while she was searching for the cats to put them outside.

S&W SD40

He allegedly shot her 10 times in places that did not kill her such as "on her lower extremities, two on her right rib, and one on her left middle finger", according to the police.

White allegedly pointed the gun at her head and said that he was going to kill her. She begged to let her call the police. In the end he called the police!

He is now in jail waiting for his trail. She must be very well bandaged with four fingers on her left hand.

He was charged with aggravated battery and aggravated battery with a dangerous weapon. In Britain it would have been 'grievous bodily harm'.

Moral: Investigate why a ledger was evicted from their previous residence and ask the person who did the evicting. Ask the landlord not the tenant. Get references etc. And specify in a formal agreement that no cats are allowed or one cat is allowed. It seems that this was a poor informal, verbal agreement. These are distinctly dodgy. As dodgy as Mr. White.

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P.S. please forgive the occasional typo. These articles are written at breakneck speed using Dragon Dictate. I have to prepare them in around 20 mins.

Model with chronic back pain hits rock bottom and rebuilds her life with cat sitting franchise

A model has told The Sun newspaper that she hit rock bottom at one stage when she was a model because she developed chronic back pain which the surgeons could not fix. She had numerous operations which failed to resolve the problem but left her back looking a mess and at one stage she was confined to her bed in agony, contemplating suicide. She went further and tried to end her life but she was found the next day unconscious.

Helena when she was modelling. Image: Focus Features.

Her name is Helena Abrahams and she is now 52 years of age. She is a cat lover. She lives with nine cats. Her cats gave her inspiration to start a cat sitting business which proved highly successful. She now runs a franchise and has franchisees all over the country and she turns over £100,000 annually. She is making a good living thanks to her love of cats and getting her health back.

After multiple back operations. Image: Focus Features.

And she praises her cats for seeing her through the darkest days of her illness when she was surviving on Pringles because she had no money for food and any money that she did have she spent on food for cats.

She now has a successful business and a bright future. What is the moral of the story? Cat companions can see you through your darkest hours and give you inspiration to climb out of the abyss of despair and gradually build towards the zenith of success!

I will add a bit of detail to that overview of her story. She said that her whole career was based around her looks but because of her back pain and the multiple operations the surgeons "butchered" her back. It looks a mess but fortunately now after all these years it doesn't hurt as much.

She was even compelled at one stage to sell some nice jewellery that her parents had given her as a present. She had to pay her bills somehow. She had a relationship and that ended. She wasn't seeing anybody except her dad. In her late 30s she could no longer cope. Before she tried to end her life, she wrote letters about her cats to make sure that they went to good homes. She overdosed on the medication that she was using for her back pain.

She said:

"My cats really pulled me through the recovery, so it was natural for me to want to give something back. I really do care about cats, and how they are treated, and my clients see that. I treat every cat as though it is my own. I love working with animals and they have really turned my life around. I am still in pain, and I will need further surgery in the future, but I have so much to celebrate now. I have learned to see my scars as part of my journey, part of who I am."

She added: "For anyone who gets to that low point, please don't despair. There is always hope."

Are cats in multi-cat homes more stressed and if so does Feliway Friends help?

A grand multi-cat home. Highly organised and harmonious! Image: Pinterest.

To answer the first part of the question in the title: a study suggests that the number of cats in a household does not significantly impact the level of stress in individual cats. Other factors, such as the relationship with their owners and the availability of resources, may be more important in determining a cat's level of arousal and emotional distress. The study also found that young cats in multi-cat households had lower levels of stress hormones, and that cats who tolerate petting by their owners tend to have higher levels of these hormones (don't like being petted?). These findings suggest that social interactions and positive human-cat interactions may play a role in reducing stress in cats.

There will be some homes where stresses might build up because of the multi-cat environment where they wouldn't normally.

However, a review found that the available evidence on the impact of single versus multi-cat housing on stress in confined cats is limited and inconsistent. While some studies suggested that single housing may be less stressful for cats, others suggested that group housing was less stressful. The review also identified several other factors that may impact a cat's level of stress, such as the socialization status of the cats, the handling and enrichment provided, and the way in which groups were assigned. Overall, the review concludes that more research is needed to determine the optimal housing conditions for confined cats in order to maximize their welfare.

Do artificial pheromones work?

Another study evaluated the effectiveness of a new pheromone product (Feliway Friends) in reducing aggression between housemate cats. The study was a randomized, double-blind, placebo-controlled pilot trial involving 45 multi-cat households with 2-5 cats each. The participants were given instructions on how to handle aggressive events and were provided with plug-in diffusers containing either the pheromone product or a placebo. Aggressive events were monitored using the Oakland Feline Social Interaction Scale (OFSIS), which assessed the frequency and intensity of 12 different aggressive interactions. The results showed that the use of the pheromone product significantly reduced aggression between housemate cats over time. The study concluded that the pheromone product is a promising treatment for managing aggression in multi-cat households.

The 3 studies in order:

• Are multi-cat homes more stressful? A critical review of the evidence associated with cat group size and wellbeing
• A critically appraised topic (CAT) to compare the effects of single and multi-cat housing on physiological and behavioural measures of stress in domestic cats in confined environments
• Evaluation of the efficacy of an appeasing pheromone diffuser product vs placebo for management of feline aggression in multi-cat households: a pilot study

Comment: domestic cats are very adaptable. At home they have food, warmth and security. A degree of cooperation is needed to keep the group in relative harmony to take full benefit of the rewards on offer.

A source of food is a great motivator for cats to be sociable and get along as best as possible with home ranges that are much reduced from their natural size.

Note: I have deliberately relied on studies as they avoid anecdotal evidence which is often dubious. However, the summaries of the studies are in plain English.

Cat owner calls the police because her two cats were fighting and one of them attacked her

OMAHA, USA-NEWS AND COMMENT: This is, for me, a case of very poor cat management. It appears to me that the woman simply lost control. The story also points to the problems that can arise when you adopt a new cat into the home of a resident cat i.e. your first cat. It can go badly wrong.

Feline aggression. Generic image. Not the cat. Image: Pixabay.

In this instance a couple of cats living in an apartment near 37th and Dodge streets, were fighting. The 52-year-old woman owner tried to intervene but one of her cats retaliated when the owner called timeout. I'm not sure what that means in this instance but it seems that the owner tried to intervene and was quite strict with the cat in telling him off, who, rather than submitting, retaliated and attacked the woman.

RELATED: Famously violent cat ‘Lux’ may have been systematically abused by man living in the home.

As a consequence, the owner called the police for help. Mistake 🤔. What were the police going to and in any case, it was not a police matter? There was no crime. The woman then said that she was able to lock the aggressive cat in a bedroom. The woman received a multitude of superficial scratches and treated at hospital. The cat was taken into custody by officers from the Nebraska Humane Society. We are not told what happened to the cat. I hope he is rehomed.

Comment: it seems to me that this was a house where the two cats were not getting on. There was a fight and the owner tried to intervene without success. One of the cats fought back and scratched the lady. It all seems rather typical. The problem appears to have originated in incompatibility between two resident cats. The woman mishandled the "argument" between the cats.

It would have been better if she had simply placed one cat in one room and the other cat in another room to allow them to cool down and used thick gloves for protection. She could have tried some tricks to stop the confrontation such as introducing a favorite toy to play with and/or catnip and/or some treats. These may have cooled tempers and distracted the cats.

If there is an underlying and unresolvable hostility between the cat then she would have to seriously consider rehoming one of them. That would certainly resolve any simmering hostility between the two.

It was, in retrospect, ill-advised to try and tell off a cat that was in an aggressive confrontation with another cat. It may be the case that the aggressive cat transferred their aggressivity towards the lady in a kind of repositioned or redirected aggression. The aggression was meant to be made against the other cat but it ended up being made against the woman.

Woman allowed 6 cats under a rental agreement but keeps 11 and is now in trouble

WEST BROMWICH, UK-NEWS AND COMMENT: Midland Heart is a company providing affordable rental housing in the Midlands, UK. It seems to me that they have generous rental agreements because they have allowed this mother, Lindsay Simcox, 43, to keep six cats in her home. I don't think many housing associations would allow that, normally. To get permission to have one cat is pretty generous and six is exceptional. Despite those terms and conditions, Simcox kept 11 cats in her home with her autistic children.

Lindsay Simcox and cat. Photo: Birmingham Live.

When I read these stories, I become very cynical. It is hard for me to adopt a generous spirit because I think this woman is playing the system. I don't think she works and she gets benefits which probably includes housing benefit. She is clearly very obese and has breached the terms of the rental agreement very conclusively. I also think that it is impractical to have 11 cats in a small home. However, despite the large number of cats, she keeps the home clean which indicates that she is making real efforts to look after them properly which is commendable.

She says that her children benefit greatly from the presence of the cats. And it is known that autistic children can benefit from interacting with animals. The point is this: she's been told by a representative of Midland Heart that the cats have to go because he has four dogs as well! Can you imagine? She has 15 animals in what must be a small home. It is just not viable.

The housing company has threatened legal action unless she gets rid of the cats. She is desperate because her children love the cats and she doesn't want to tear them away from her kids. She is not under threat of eviction but she is under threat of legal action for an injunction i.e. a court order which states that the cats must be rehomed.

Simcock said that she was ratted-on by a neighbour who probably doesn't like her or took offence to the fact that she has so many animals in her home. They might cause a nuisance to neighbours which is likely because it is very difficult to keep 15 pets in the home without affecting neighbours in terms of smells and noise.

Comment: the cats will have to be rehomed and it probably will do them good because I don't think it is a good idea to have 11 cats banged up together in a small home like this. They may be well looked after or at least to a reasonable standard but in terms of the amount of space they have it is unsatisfactory. Although domestic cats are of course very adaptable.

Help for skittish kitties?

Your cat is skittish. You want to help. He or she is probably skittish for three main reasons (1) he is timid and shy or (2) he is in a new home and has not settled down properly or (2) the home is unsettled in terms of ambience.

Background animosity between humans and cats can make a cat skittish through anxiety. Image: MikeB

The last factor I think is a key one. It is now common knowledge that domestic cats like to live in a calm environment with solid routines and rhythms which are integrated with their human caregiver. If you add into that a home which is adapted, at least to a certain extent, to a cat's behaviour plus plenty of play a cat should not be skittish for environmental reasons. It would be hard to shake skittishness due to timidity which is inherited. The best you can do there is to once again create a very calm, friendly environment to enable a skittish cat to feel calmer and become more confident in their environment.

Skittishness is a product of anxiety or fear. This, as mentioned, can emanate from an inherently shy character. But if the cat is not inherently shy but is still skittish it's going to be environmental factors which cause this. In a multi-cat home, there may be bullying by a dominant cat or a cat might not get along that well with the other cats. It is said that at behavioural problems most often start in multi-cat homes where domestic cats are brought together in a confined space. This is especially true if they are all full-time indoor cats which is probably going to be common for the simple reason you can't let a lot of cats outside to roam freely.

The kind of person who keeps a lot of cats as pets is also the kind of person who keeps their cats indoors all the time. This can build up some anxieties in some cats if they lack confidence. It would be hard to beat this problem. What I mean is if a cat is skittish because they feel unsettled due to the other cats around them, there is no cure for that other than separating the cat from the other cats which is not going to be practical.

Play is a great way to bring a shy cat out of their shell. They forget where they are when they are playing because their instinct takes over and they chase and hunt a cat toy. It also helps to create a stronger bond between person and cat. With a stronger bond a cat is likely to feel more settled and therefore less skittish.

It all comes down to the environment. At one end of the spectrum, you might have a retired person like myself living with one cat. If that cat has a normal character i.e. neither nervous or overconfident, then they will be calm and they will not be skittish. It may occur temporarily for some extraordinary reason but in general they will be calm. At the other end of the spectrum, you might have a home where people come and go all the time, which is noisy, and where there is more than one cat. This sort of home opens up the door to a lot of potential conflicts or situations which could unnerve a domestic cat even one who is not inherently skittish.

It may be impossible to make that noisy, active and unsettled home into one which is calm and quiet for practical or functional reasons. In which case the cat will not lose their skittishness unless they are able to adapt to it. Domestic cats are very adaptable and they can get used to some extraordinary situations. I have seen a community cat in Asia sleeping at the top of an underground railway escalator at the exact point where the passengers leave the escalator. Clearly that cat is completely adapted to a noisy and active environment.

One big problem for domestic cats is ensuring that they have enough space i.e. their home-range. If they are able to enjoy their home range, which they feel they can control, it does help to calm them. And skittishness overlaps with aggression. Domestic cats who suffer intrusions into their home range can become defensively aggressive which may be perceived as agitated or even skittish by some observers. Once again it is down to the environment.

The last resort in dealing with a skittish kitty is to consider drug treatment. I'm talking about tranquilizers for domestic cats. It does happen but I think you have to be quite desperate to take this route. All the other normal steps must take place first because drugs simply mask the symptoms whereas what I discussed on this page gets to the root of the problem.

As an afterthought, if the problem is the other cats in the home, then creating a room or rooms which are for the exclusive use of the skittish kitty and their human caregiver will certainly help the cat to recover some confidence.

And it might be easy to forget about the skittish kitty because he or she is hiding some of the time. Out of sight out of mind is the motto and this can happen with domestic cats. People are too busy and they take it for granted that cats are "independent" when they are not in truth. But leaving an anxious kitty alone without plenty of human interaction of the right kind will make her condition worse.

And of course, it goes without saying, that patience is a vital ingredient in getting a wallflower to bloom. Jackson Galaxy calls timid cats 'wallflowers' but you can get them to bloom. They have to believe that the place where they live is not hostile but is very friendly. If you achieve that he will be relaxed and come to you.

To conclude, the key to helping a skittish cat to feel calmer is to ensure that the environment is as suited as best as possible to a feline character. In the words of Jackson Galaxy, the owner needs to tap into the raw cat beneath the domestic cat to find out what makes them tick. This will allow them to find their mojo which means to behave normally in a balanced way.

Video example of antagonism between cats in multi-cat household

This lady bought some new cat shelves which attach to the glass in a window frame through suckers. It's quite a clever idea as cats love to look outside and high vantage points. She is pleased that they work. She is not going to be pleased that her cats are fighting. It looks like a minor contretemps between two family cats in a nice home. 

Video example of antagonism between cats in multi-cat household. Screenshot.

They, are no doubt, well looked after and loved. But my guess is that there is a background of quiet, simmering animosity between these two cats. They probably get along pretty well nearly all of the time. But they both jumped onto these new cat shelves to try them out which put them close together and a slapping competition commenced.

CLICK FOR A PAGE ON FIGHTING IN MULTI-CAT HOMES

This is an embedded tweet. They often go caput because they are pulled from Twitter. Sorry if that's happened. You have a still image instead which is nowhere near as good.

Was looking at “cat shelf” reviews and found this truly perfect user-submitted video: pic.twitter.com/s7IzHpg5e2

— Carlos Maza (@gaywonk) August 24, 2021

The experts say that if there is a cat behaviour problem described as "bad cat behaviour" in a home it's often caused by friction between cats in a multi-cat household. If that isn't the cause it is going to be the behaviour of the human caregiver which has rubbed up against feline emotions.

Adopting a second or third cat into a home is a problematic process which should be carried out with great care. Rescue centres should allow people to "suck and see" when adopting a second cat. They should allow them to bring the cat back after a week if it doesn't work out. Perhaps they do this in some shelters but it should be the default policy.

You get chemistry between cats. We don't know why some cats get along and some don't but I'm going to propose that the reason is a common sense one: they just get along like people get along because it's the right chemistry. But the big issue with multi-cat homes is that you are putting cats quite close together; unnaturally so. 

Domestic cats need several acres at least of home territory and they have to adapt to a much smaller space especially if they are confined to the home. They do this but it is easier for some cats compared to others. This is likely to cause stress if the cats are not friendly with each other. This is what has happened in this instance in my opinion.

Domestic cats are not adapted to living in close proximity to each other

The title presents an interesting thought and it directly impinges upon what goes on in multi-cat households. Although domestic cats are social creatures and they can live in groups those groups need to be stable and the cats should be socialised to each other. In other words, the cats should be selected to get on with each other and ideally no new cats should be brought into the group which might destabilise it.

Domestic cats are not adapted to living in close proximity to each other. Montage: MikeB from images in the public domain.

Domestic cats don't have classic hierarchies when living in groups and they don't have signals which help to defuse conflict. Further, they don't have mechanisms such as reconciliation as discussed in studies by van den Bos & de Cock Buning 199b and van den Bos 1998.

In the wild, if there was conflict between cats, they would disperse to avoid each other and often this is impossible and in multi-cat homes and it certainly is impossible if they are living full-time inside a home. This is exactly what is happening with my neighbour about 4 yards from me right now. She has 10 cats and she hasn't got a clue as to what she's doing in terms of how the cats feel when they live in such close proximity to each other as far as I can tell.

One of the major reasons for the creation of behavioural problems in domestic cats such as timidity, fear and avoidance behaviours come about because of what is called environmental stressor i.e. things that happen in the environment in which they live which stress the cats. A high proportion of the stressors are concerned with the relationships between the cats and the relationship between the cats and people living in the home. This was found in a study by Casey and Bradshaw in 2000.

Sibling pairs of domestic cats more often have amicable relationship compared to unrelated cats when living together. Although, I think it is fair to say that not all siblings get along when they become adults because at that time they become independent. It's just that there is a greater likelihood of the siblings getting along in multi-cat homes.

A point comes to mind. Jackson Galaxy says that when you adopt a cat from a shelter you might adopt a pair if the shelter knows that they are known to get along. I guess that makes sense but not infrequently cats are rescued as a pair and then they are rehomed as a pair for obvious reasons. When two cats get along well, both their lives are enhanced and they should stick together. It is not only better for the cats it is also better for the cats' caretaker because they can entertain themselves and enrich the lives of each other.

When cats are introduced to each other as adults they may not regard each other as part of the group but they are sometimes regrettably forced to live together in close proximity which may lead to agonistic behaviour. 

Aggressive encounters may occur not infrequently between cats living in a high density in the neighbourhood. I'm referring to indoor/outdoor cats. This is a typical situation in the UK for instance. Under these circumstances some cats may become frightened of going outdoors. The other, more dominant cats will be attacking the timider cat when in a public area.

It is wise for cat owners particularly in condominiums and blocks of flats to be aware of this interaction between cats in the common parts within these complexes.

Ref: Cat Sense by Dr Bradshaw.

This domestic cat is a pacifist

One of these cats is the aggressor and the other, the star of the video, is the pacifist because she strikes a defensive pose as if to say, "Stop that, it's enough". Her behaviour reminds me of Japanese martial arts. The pacifist cat is the tabby-and-white while the aggressive one is a tabby.

No one:

Professor McGonagall doing spells, forgetting she's still a cat: pic.twitter.com/gQOntA9QJT

— Professor Snape (@_Snape_) November 29, 2019

Cat Food Wars - Dominance and Subservience

This is not exactly a war over cat food but you can see how stresses can be built up in multi-cat households in areas where there are food bowls and where there is the cat litter. Cats will or might compete for either. These are areas where a hierarchy between cats is shown up and where a dominant cat will push out a more subservient cat.

I think this is quite an interesting animated GIF, which are a series of still images strung together to make a video that repeats itself. Each image is in the GIF format.

Clearly in this instance the ginger tabby is dominant over the bicolour ginger and white who is overweight so perhaps being pushed out of the food bowl is a good thing. I wonder if the slight overweight problem that the bicolour cat has is linked in any way to his or her subservience to the ginger cat? Perhaps he's pushed out and therefore he is keen to get at the food when there is a chance and hence he eats too much as a precaution against not being able to get to a food bowl when they are put down.

The experts would say that it is important to make sure that a subservient cat has a place to hide and then each cat gets its own food bowl and as best as possible is allowed to get to it. Cat litter trays should also be considered carefully in multi-cat households because you can get competition around a cat litter tray. All this means is that the subservient cat is liable to become stressed and it is a cat owner's duty to make sure that all her cats are content!

This does, though, seemed to be a setup situation. Although, it does not detract from what can go on in multi-cat households.

Requirements of Cats Kept in the Home

The requirements of cats kept in the home is important in America but less so in Britain for the obvious reason that a lot more cats are kept indoors permanently in America than in Britain. There is a definite culture difference with respect to cat caretaking between the countries. One reason may be that there are more purebred cats in the US and also going outdoors may be more hazardous with respect to predation by wild animals.

However, keeping cats indoors reduces the home range for the cats significantly. It also places individual cats in close proximity to each other. However studies indicate that neutered male and female domestic cats can be housed successfully indoors if there is enough space of sufficient quality and provided the cats have become used to these sorts of conditions from kittenhood. Cats require more space than we think and they need to be able to get away from each other and and out of sight of each other from time to time.

Harmonious group - Photo by Bibi

In one study¹ of 14 cats who had 10 square meters of space each, it was found that most of the cats had a favorite spot. Sometimes a spot was shared and sometimes a spot was unique to an individual cat. In sharing places cats lived peacefully together by time sharing these places and thereby avoiding each other.

Male cats have larger home ranges than female cats generally and this is demonstrated in respect of full-time indoor domestic cats. In this study males had ranges of 4-5 rooms while females had ranges of 3-3.6 rooms. Females are therefore slightly more suited to indoor life.

Another scientist² recommended two resting places for each cat; one on the floor enclosed on three sides (my comment: for a cat to hide and feel safe. What about protection from above?) and the other should be elevated with a good viewpoint (my comment: there is no doubt that cats like high vantage points and can spend long periods on perches). This recommendation is important in preventing behavioral problems in multi-cat households.

In addition, positioning scratching posts or a "scratching surface" (my comment for posts: large, heavy and tall) at places of exit and entry in the home and near sleeping places is helpful. Litter boxes should be in quiet areas. They should be cleaned daily.

Another species of companion animal such as a dog is beneficial provided the cats are socialised to dogs. Elisa, a regular contributor this this website has a dog, Dreyfuss who loves cats and the cats in her home often love him and rest on him. Elisa has a harmonious multi-cat home. Elisa's caring, cat orientated input contributes greatly.

Interactions with the human caretaker are important. Domestic cats are not "adapted to living in close proximity to each other". Moving away and dispersing to avoid aggression is harder for a full-time indoor cat. Cat behavior problems can be due to stressful environmental situations - "social factors". This is a reference to interactions between cats and cats to human.

Related cats are more likely to get on that unrelated cats. Four or more unrelated cats in a house are more likely to have behavioral problems than less cats that are related.

Cats introduced to a multi-cat household are chosen by the owner and these cats may not get on. They may not see each other as part of the same social group and be forced to live in close proximity to each other. This is likely to cause stress.

Associated:

1. The Multi-cat Household
2. Multi-cat Household

Reference:

1. Mertens and Schär 1988
2. Schroll 
3. Generally: The Welfare of Cats ISBN 978-1-4020-6143-1