Many species of birds migrate long distances to find food or better breeding grounds. During migration, birds often molt, which is the process of losing and replacing old feathers with new ones. Molting is a very energy-intensive process, and it can make birds more vulnerable to predators. As a result, some species of birds have evolved to desert their offspring during migration in order to focus their energy on molting.

This behavior is known as "brood desertion," and it is relatively common among migratory birds. Some species of birds that engage in brood desertion include cuckoos, cowbirds, and some species of waterfowl. When these birds desert their offspring, the young birds are left to fend for themselves. They may have to find food and shelter, and they may also have to avoid predators. However, many of these young birds are able to survive and eventually fledge.

Brood desertion is a controversial behavior, and it has been the subject of much debate. Some people believe that it is cruel and unnatural for birds to desert their offspring. Others argue that brood desertion is a necessary survival strategy for many migratory birds. Ultimately, the decision of whether or not to desert their offspring is a complex one that is made by each individual bird.