ELI5 - Why do mother birds eat their young?

This sounds scary, but it helps to know that it is not about being mean or cruel. It is about survival.

First, most mother birds do not eat their babies most of the time. When it does happen, it is usually because something has gone very wrong. Birds live in a hard world. Food can disappear. The weather can turn bad. Predators can show up. Birds have very little room for mistakes. One reason this can happen is lack of food. Baby birds need to eat almost constantly. If a mother bird cannot find enough food for all of them, the weakest baby may not survive. In some cases, the mother will eat a chick that has already died. This gives her energy and removes smells that could attract predators. To a bird, this is a practical choice, not an emotional one.

Another reason is sickness or weakness. Sometimes a baby bird is born very sick, injured, or unable to grow properly. The mother bird can often tell. Keeping a sick chick can risk the whole nest. Disease can spread. Extra crying can attract danger. By removing that chick, the mother increases the chances that the stronger babies will live. Stress is another big reason. Loud noises, constant disturbance, pets, people touching the nest, or predators nearby can overwhelm a bird. When birds are extremely stressed, their instincts can break down. This can cause unusual behavior, including harming or eating their own young. This is more common in captivity, like pet birds, but it can happen in the wild too.

Sometimes first time mothers also make mistakes. Young birds are still learning how to care for a nest. If conditions are bad, their instincts may push them to give up on the brood entirely and try again later when things are safer. From a human point of view, this feels awful. Humans are wired to protect babies at all costs. Birds are wired to protect the survival of their genes. Their goal is not to save every chick. Their goal is to make sure at least some chicks survive.

So when this happens, it is not cruelty. It is nature being harsh and very efficient. The mother bird is making the best choice she can with the instincts she has, even when that choice looks heart-breaking to us.