Rodents such as hamsters, gerbils or mice usually eat some of their young. What a priori may seem like unnatural behavior and contrary to the theory of the evolution of species, the truth is that this act of cannibalism only refutes it. There are many reasons that can lead your pet to eat its young that, as much as they believe you are repulsed, remember that they do it for practical reasons.
The objective of a mother that ingests her young, paradoxical as it may seem, is none other than to ensure the preservation of the species. Rodents have a tendency to give birth to many young at a time and in the animal world resources are limited. Various studies support that females make a kind of calculation with these two variables to optimize the amount of food —mainly breast milk— that they have available to get their litter ahead.
A mouse with a dozen offspring will be able to eat a couple of them to guarantee the survival of the rest. This hypothesis has been experimented with in laboratories, so that, with the same resources, the more pups the female has, the more she will eat and, conversely, if the number of pups is low, the ingestion will not take place.
Cannibalism is a purely human concept since, for animals, dead conspecifics are a source of protein that cannot be wasted. A dead hatchling is also a potential source of infection and an attractive defendant for predators and scavengers. That is why, for mice, eating stillborn or prematurely deceased pups is a natural reaction that provides more nutrients to the milk that the rest of the offspring feed on, while maintaining the clean nest of putrefaction.
Stress is one of the factors that can induce a female to eat a healthy calf. This is because the mice are not aware that in captivity all their food needs will be covered, so if they lack food at a certain time, they probably consider that they have to eat a young for the litter to be viable.
Strange odors will alert the female, who will interpret it as a threat. The mouse will end up disowning and eating the baby that smells different, so it is important to leave them alone for fifteen days after they are born. It should also be avoided that females become pregnant before two months of life, when they already have the maturity to raise a litter.