Unlike some of the other myths I’ve covered, this myth has been prevalent for decades and probably arose from parents not wanting their children to touch any baby birds they find on the ground.
Despite the widespread belief that touching a bird will leave a human scent on it and therefore make other birds reject it, the story is absolutely false.
Birds have a terrible sense of smell, so the idea that they can smell the scent of humans on a baby bird is pretty crazy. Someone once said the idea was akin to a human mother smelling a bird that landed on the top of her child’s head and then no longer wanting them in her house.
Scientists and researchers have been handling baby and adult birds for years without birds abandoning the baby or ostracizing an adult from the flock. All this is not to say you should go around touching birds in nests.
Occasionally, a bird will abandon its baby if it sees a human coming around and grabbing the baby too often. The mother doesn’t smell a human on the baby, but might perceive there to be extreme danger and risk to herself and the baby from constant activity. Generally, this type of behavior is not very common since the mother will fight until the end to protect her baby.
Another reason this myth might be common is that when someone picks up a fallen bird and places it back in the nest, the mother might only come back for a little while and then fly away for several hours. There are two reasons for this: either the fallen bird was a nestling and the mother was going to find it more food or the bird was a fledgling learning to fly and the mother was giving it distant support to ensure it learned how to fly on its own. Neither of these have to do with the smell of a human.
If you find a fallen nestling on the ground and see the nest within sight, there won’t be any risk of picking it up and placing it back. However, you should always avoiding picking up wild birds unless absolutely necessary.