<p>It is pure instinct. The baby chicks can smell and hear their mother. They have been listening inside the egg and know their mothers call. This is nature working at it's very best and the mother is looking out for her young so they always meet up. The mother can hear the chicks calls so if she isn't right there she will come.</p>

<p>Well its hard to say but I'll do my best to explain it.</p><p>As far as ducklings go, they are what are known as precocial birds (birds that can walk immediately after hatching). These birds actually hear their mothers voice when they are still eggs and after they hatch, the first person that they see is their mother, who has the same voice they'd been hearing while they were eggs, thus, they conclude that this person must be worth following or in this case, their mother.</p><p>That's how things go in a perfect scenario but it's also possible for one animal to imprint on another species of animal. That kind of imprinting is called filial imprinting and it's actually not that rare. There's been a lot of studies on animal imprinting but there are two main factors of imprinting;</p><p>1. It happens during a critical period which is about 13-20 hours after the bird hatches and the more stress involved in finding the mother increases the strength of the imprint.</p><p>2. It is permanent and can't be reversed. If a duck imprints on a ham being, then it's not going to imprint on anyone else(kinds reminds you of Jacob in twilight). </p><p>As far as other animals like mammals go, they equally imprint on their parents, but not to the extent that precocial bird to and this is because precocial birds can move once they're born and can find their mothers. I also want to note that the reason for printing often has nothing to do with genetics, it's more instinctive than anything else.</p>