Each year hundreds of animals are taken into care by humans for various reasons ranging from oil spills to injuries from barbed wire fences to non-deadly car incidents. As Konrad Lorenz discovered, certain animals experience the process of imprinting, meaning that an animal becomes largely fixated on (Generally) the first thing it sees. However, the time that imprinting occurs can range from a few hours to a few weeks, such as the case in large birds of prey. Incidentally, when some birds are taken into care, their offspring may become fixated on a human being that steps in to care for the animal.
Imprinting is not entirely bad though, when it happens in a natural environment. It helps prevent young being separated from their mother, consequently helping them learn and observe important survival techniques. Imprinting may help explain those crazy stories of ducks following zebra's around like they are their mother at zoos.
One important thing to understand about imprinting is that it's irreversible . Once an animal, usually a bird, fixates on something it will never change. If an animal imprints on a human, it will always prefer humans over animals of the same species. This is why it's tricky releasing animals from zoos or rehabilitation facilities.
Another problem with imprinting is that birds look to their siblings for examples of behavior. This later on in life, influences mate selection. If an animal imprints on the wrong species, reproduction doesn't look too good.
Take this as a warning, if birds hatch in your yard either A) Don't interact with them or B) Bring them into a wildlife care center. As described in this article, it would be awfully sad to drop of a bird and a wildlife care center while it thinks you are it's mother.
Sometimes we can get some humor out of imprinting, such as this fad of marching ducks that's sweeping (Rather marching) across Europe.