In A Nutshell
Hamster cannibalism is not uncommon. When a hamster gives birth, she may feel pushed to eat some or all of the new pups. This may be a response to lack of resources (like food, space, or protein), fear of a perceived threat, or some type of confusion.
The Whole Bushel
What could cause a cuddly, harmless, predominantly vegetarian rodent to ingest its newborns? As it turns out, lots of things: It doesn’t take much to push a mother hamster into eating her new babies.
One theory suggests that the mother eats her young as a way of compensating for lack of resources. Eating some of the pups gives the mother the extra protein she needs to lactate enough milk for the remaining pups. Additionally, the mother may calculate that there’s not enough food to go around for her entire litter—or that the cage the new family lives in is too small to house everyone. In that case, rather than let the runts die out, the mother proactively makes some cuts.
Fear may also be a factor. The shock of birth may cause the mother to perceive her pups as some kind of threat that needs to be eliminated. Additionally, an outside threat may cause the mother to believe that eating her pups is for the best: either to reduce her own workload in a high-pressure situation, or because there’s a good chance they were going to be eaten anyway (and she might as well eat them instead).
Runts or abnormal pups (common to first-time moms) are rejected outright. Similarly, if a pup is handled too early by a human or is born outside the nesting area, the mother will, again, reject it and treat it as a food source. This is likely because the scent of a human is associated with food.
Hamsters aren’t the only child eaters: Polar bears, burying beetles, wolf spiders, and sand goby fish (among others) also practice infant cannibalism. The male sand goby fish is responsible for raising the young that he produces with two females at a time—but he’ll eat up to one-third of the eggs before they’ve hatched. He even targets the bigger eggs, understanding that they require more work to nurture. Less work equals less time before he gets to mate again—and produce thousands more eggs.