Adaptive Value
If the parents waste some of their resources on a genetically unrelated offspring and chicks are usually abandoned (often fatally) within a few hours, who exactly is benefited by kidnapping behavior? One paper suggests that chicks actually do benefit from being kidnapped as well as from other forms of adoptive behavior, as their food intake increases and they gain protection from giant petrels simply by the presence of adult penguins. They also gain protection from the cold for whatever amount of time they are being looked after. However, in most cases these benefits are short-lived and the babies also have a 6% chance of dying while their parents battle the kidnappers. For the parents, kidnapping presents most of the energy costs (as well as risk of injury in the aforementioned fights) and none of the benefits of general parental care, so the behavior is a bit confusing and might even be pathological.