Males Killing Kittens
Although cats are often considered to be purely solitary, in the feral and the domestic situation they are frequently organised in social groups similar to the social grouping of lions (prides). These groups are matriarchal in nature i.e. dominated by the females, and often the males will only be in attendance when a female is available for mating (though this rule is flexible and some groups will have a resident male). A tom cat will normally establish a territory which contains a number of females or female groups, and it is in his own interest to repel other males and to destroy kittens which may have been fathered by another male and which contain the genetic complement of his rival. This is true of many social animals, relatively few of whom will expend their own energies in raising the offspring of another male.
How do males know who has fathered the kittens? Cats rely greatly on scent and scent markings to determine who is present in their territory and who has visited that territory. If a tom smells the scent of a rival tomcat he may decide that the kittens belonging to his 'harem' have been fathered by the visiting tomcat. This is not in his own genetic interests. Consequently he may kill those kittens. This has two purposes. Firstly it ensures that his queens do not raise kittens fathered by a rival male. Secondly, the queens will usually come on oestrus within a few days and he can be sure of mating them so that subsequent kittens are his.
When a new tomcat takes over or inherits a territory (the former territory owner having been removed, neutered and thus non-competitive, or dead) he may also be driven to destroy any kittens in order to 'found his own line'. A territory can be something as small as a single room in the house. These are all fairly anthropomorphic terms describing an instinctive drive to give his own genes the best chance of survival.It is an over-generalisation to state "tomcats are just like lions, they kill kittens so they can mate with the females" as it depends on how many toms are competing over the females i.e. is linked to rivalry. Itinerant tomcats cannot be certain whether the kittens are theirs or were sired by another visiting male and thus kill all kittens below a certain age (it is in the mother's best interest to hide kittens while they are vulnerable). A few tomcats seem to be genuine rogue fathers and kill kittens that they have sired. This is an aberration and is self-limiting - by killing their own offspring, their genes will not be passed on (except in breeding programmes where the male has no access to his offspring).
Some tomcats are more benevolent in their approach, perhaps they lack this instinctive drive or it is less well developed. It also seems related to the lack of other tomcats in the area such that the male is in a less reactive state. Some breeders raise the kittens with both parents present, again, there is usually only the one tomcat around. Neutered toms, as a whole, tend to be more benevolent due to their hormonal state (or lack of a hormonal state). These toms may tolerate kittens which are not their own, only driving them away (through fighting) as the kittens become sexually developed.
Although in the main, toms do not contribute to the raising of kittens, there have been instances where even unneutered toms may supply food, tend or move the kittens or be willing to play auntie even to the extent of allowing the kittens to 'suckle'. A few males have even taken over the majority of mothering duties (apart from milk production) from incompetent females or where kittens are orphaned. A potential problem arises when the kittens play. Most female cats can switch between 'play mode' and 'hunt mode' in order not to harm their offspring. In tomcats this switching off of 'hunt mode' may be incomplete and when they become highly aroused through play, the 'hunting' instinct comes into force and they may kill the kittens. The hunting instinct is so strong, and so hard to switch off when prey is present, that dismemberment and even eating of the kitten may ensue.
The automatic response of a young kitten being held in a nape-of-neck grip is to go limp to allow the mother to lift and move it. Neckbiting is an activity found in both mating behaviour and in dominance behaviour (which does occur between cats, though not as often as it occurs between dogs). A tomcat may attempt to assert dominance over a kitten, particularly an unruly one, and in doing so may break the kitten's neck. A tomcat which has been attracted to a nursing female may attempt to mate the female (her hormonal state invites sexual advances), but if he is repelled he may then attempt to mount a kitten instead (a displacement or frustration activity giving an alternate outlet for the mating urge). Again, the force of his jaws may break the kitten's neck.
Compare the size, sound and activity of kittens with the size, sound and activity of prey. They are both small, have high-pitched voices and move with fast, erratic movements. All of these trigger hunting behaviour. In the tomcat, maternal behaviour cannot always override hunting behaviour and he treats the kittens in exactly the same way he would treat small prey. His instincts are confused; he simply may not be able to override the hunting response triggered by the combination of size, sound and movement even if he is normally non-aggressive towards kittens. Some females cats act the same towards other females' kittens.
Finally there is the question of whether queens protect their kittens against marauding tomcats. In the lion pride, females defer to the male e.g. in relinquishing prey to him and also make little attempt to defend cubs from his attacks. The cat social structure is less well defined. Unlike lion prides, tomcats are present for less of the time and females are less submissive. Communally nesting queens have been seen to drive away attacking males. A colony's 'resident' tom may also drive off a marauding males though probably in response to territorial instinct rather than any attempt to actively protect his own offspring. Whether a queen defends her kittens probably depends on her presence (most male attacks occur when the female is away from the nest), her physical condition (ability to defend the kittens and not sustain injury herself) and her size (she may be smaller and less powerful than a tomcat). Most queens will defend their litters against attacks from larger animals e.g. bobcats, coyotes, dogs so it is likely that they will also defend against tomcats. The fact that tomcat attacks on kittens have mostly been seen when the queen is AWAY from the nest suggests that the females will indeed protect their litters against other cats. This is not a certainty since too few kitten-killing instances have been observed from which to draw firm conclusions.
Females Killing Kittens
Kitten-killing is more often seen in females, simply because the tom is usually absent from the nest. There are numerous reasons for this behaviour.
As in tomcats, some females cannot switch off hunting behaviour in response to the presence of kittens. Some have poorly developed maternal instincts or they may have a hormonal imbalance so that the maternal behaviour is not triggered by pregnancy and kittening. Because the kittens may inherit this as a genetic trait (hypothetical but very feasible), it is wise not breed from such females again - not just to avoid the tragedy of seeing kittens killed by their mother, but to avoid the problem becoming more widespread. Females which haven't given birth may treat kittens born to other females as prey. Pregnancy and birthing cause hormones which generally trigger maternal instinct. A female without kittens has not gone thorugh this process and the size and sound of the kittens triggers her hunting instincts.
Some kittens are born with abnormalities that humans cannot detect. For this reason they may not thrive, they may even act or smell 'wrong' to the queen. Where one or two kittens are either killed or abandoned, these kittens are often found to be somehow 'faulty'. The mother simply does not want to waste energy on raising kittens that have little chance of survival. In addition, she has expended a lot of energy during pregnancy and she may eat all or part of some of these kittens in an attempt to recoup some of those losses (just as she eats placentas) and to dispose of 'carrion' that could potentially lead predators to her nest. The same goes for kittens which have an illness - she can smell the problem, humans cannot.
Kittens born at a 'bad time of year' e.g. early spring/late fall/winter in the wild state, have a poor chance of survival due to lack of prey. A number of female cats will kill litters born at 'bad times of the year' in order not to use up valuable energy in raising kittens when they themselves have problems in finding adequate food. This has been noted in feral cats.
It is well known that a mother cat may kill kittens if the nest is disturbed, especially if she is confined and cannot move or hide her litter. This is attributed to a frustrated 'protection' instinct. Unable to protect her kittens against a perceived threat, she kills them in a futile attempt at protecting them. Perhaps instinct tells her that it is better to kill offspring herself and make good her own escape than to attempt to defend them against insurmountable (in her view) odds and possibly endanger herself in the process. A few mothers have accidentally killed kittens by trying to push them underneath a doorway in an attempt to move them to a new nest and some over-anxious but non-confined queens have killed kittens as a result of maternal incompetence or perceived threats to the nest. These mothers are generally either desperate or inexperienced or both. A few nervous queens are disturbed enough by the scent of a tomcat nearby that they will resort to the eat-is-protect mechanism.
Stressed mothers may simply decide to cut their losses. Perhaps finding that they cannot successfully rear or save their own kittens, it becomes preferable to try again at a later date or in a more favourable/safer location. However, she has invested a lot of effort in pregnancy and suckling those kittens (and in hunting for food for older kittens) so she eats them in order to reabsorb some of that energy investment. By reabsorbing the nutrients they gained from her, she will more quickly return to breeding condition and may successfully raise kittens later in the same breeding season. Some mothers will simply abandon kittens, but in doing so they lose whatever investment they put into partly rearing the offspring and might not breed again until the next season. This may also explain why some females kill some, but not all, kittens - by reducing the number of kittens in their litter, they increase the chances of successfully rearing their surviving kittens.
Sometimes she will kill the kittens because they have been handled by another person or animal. Her own scent has been obscured and she either no longer recognises them as her own or she feels threatened and unable to escape. They either become prey - in size, sound, smell and movement - or she attempts to 'protect' them by the last resort method of killing them. A female that has prevously been in an abusive situation may be anxious with kittens and may kill them as a result; stress seems to over-ride normal maternal instincts.
Where several litters have been born in one colony it is not unknown for one queen (generally the more dominant one) to either kill her rival's kittens or to 'kidnap' them. This may enhance the survival prospects of her own litter; it may remove the genetic competition from the other queen; it may be that the predatory queen's maternal instincts do not extend as far as recognising the other kittens as something other than prey or alternatively it may be that her attempts to kidnap the kittens and raise them as her own (over-developed maternal instinct?) result in the accidental death of the kittens as one queen tries to kidnap them and the other tries to defend them (even to the point of killing them herself). In a number of such cases the queens may move into a single communal nest and take turns in nursing the kittens, but in other cases some of the kittens (usually the smaller, more fragile, ones or those of the less dominant queen) die. The kidnapping of offspring is better documented in dogs, but has been observed in cats as well.
Another cause of kitten killing is rare, but not impossible. An inexperienced or over-anxious mother may clean her kittens excessively. In some cases a queen has been known to bite off a kitten's paw, tail or ear due to excessive cleaning behaviour when the kitten is small and relatively fragile. In a very small number of cases, her efforts at cleaning (and restraint) are forceful enough to kill a tiny kitten. In an attempt to hygienically dispose of the body she may consume or partially consume it.
Finally, kitten deaths occur naturally and for diverse reasons. Many queens will dispose of the body by removing it from the nest or moving the nest away from it. Another way of disposing of carrion is to eat it. Where the kitten is only partially consumed it may appear that the mother has killed it even if she is simply trying to dispose of a potential predator-magnet.
Happy Families
At the other end of the spectrum, cats in colonies (ferals, breeding catteries etc) can exhibit some truly social behaviours. They may co-operatively raise kittens along with other nursing females, with non-nursing females or even with males (most often, but not exclusively, neutered males). In most cases the participating 'aunties' and 'uncles' are related by blood, usually sisters or mother/daughter pairs who may pool their kittens or co-operate in kitten care. In most cases the kittens may have the same father (or multiple fathers since kittens in a single litter may have different fathers) or the queens may be closely enough related that the communal raising of kittens is in the genetic interest of participating queens. In the domestic setting, the co-operating cats may be unrelated but may be very familiar with one another and act as though closely related. Even if they have been mated to different toms their instincts may be fooled into allowing this co-operative behaviour especially if there is a resident stud cat on the premises - the females are unlikely to compare notes about who they actually mated with and simply view themselves as part of that cat's harem bearing litters which share a common father. Some males also become excellent and trustworthy kitten-sitters.
In a domestic situation, the owner may be viewed as 'the other queen' and it is not unknown for a female to transport all of her kittens onto the owner's lap, chair or into the bed so that the human can mind the babies while the queen takes some time out from maternal duties.
Conclusion
Fortunately the domestic cat is adaptable enough that a 'happy families' situation usually prevails. Kitten killing is more common in inexperienced or highly stressed mothers and, because the surviving kittens of a kitten killer may grow up into poor mothers themselves, there may be some genetic problems (leading to hormonal or behavioural problems) influencing kitten killing behaviour in queens. In males, the kitten-killing behaviour is most often due to their highly competitive natures, something which has been modified by selective breeding but which has not been entirely eliminated as it is part and parcel of the male instinct. Since it seems linked to the number of competing males present, it might be reduced by preventing rivalry situations. There are no studies as to whether "rogue fathers" pass on their tendencies as they rarely have access to the kittens.
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