Why do cats kill their kittens?

I am talking about domestic cats.  You can read about the traumatic act of lion infanticide if you wish. There are different motivators for lion infanticide.

Sometimes the queen (mother cat) consumes her young. This looks like very abnormal maternal behavior. It particularly concerns the firstborn.

In fact, queens routinely consume stillborn kittens together with the placenta and "products of delivery" (1). Sometimes the mother might accidentally consume the kitten while eating the placenta. Or injure a kitten when severing the umbilical cord.

Sometimes the mother may intentionally kill a kitten that is malformed or "constitutionally ill" (1).  Constitutionally weak kittens, sick kittens or deformed kittens may be ejected from the nest by the mother to die. This is the mother doing nature's work in culling on the basis of the survival of the fittest family members.

Sometimes a mother might be aggressive towards offspring because of fear, anxiety, a threat to her survival or overcrowding.

Video of mother serval giving birth and eating placenta:



(1) Cat Owner's Home Veterinary Handbook page 450.