It's a familiar summer scenario: a nest rests in the low crook of a crab apple tree. Inside, a baby oriole stretches its wings, attempting to trill. A little girl's face looms overhead. She reaches out her colossal finger to stroke the still-wet feathers. Just before contact, her father's voice booms: "Don't touch that bird!"
According to folklore, birds will reject their eggs and young if humans have so much as laid a finger on them. This prevalent belief, however, is for the birds: it denies animal parents' innate drive to nurture their broods and ignores a bird's basic biology.
No matter how flighty birds appear, they do not readily abandon their young, especially not in response to human touch, says Frank B. Gill, former president of the American Ornithologists' Union. "If a bird's nest is disturbed by a potential predator during the nesting or egg-laying stage," he says, "there's a possibility that [it] will desert and re-nest. However, once the young are hatched and feeding, [their parents are] by and large pretty tenacious."
The myth derives from the belief that birds can detect human scent. Actually, birds have relatively small and simple olfactory nerves, which limit their sense of smell. There are very few birds with extraordinary olfaction and these represent specialized adaptations. For example, turkey vultures are attracted to methyl mercaptan, a gas produced by decaying organic matter (and added to natural gas to make it smell bad), while starlings can detect insecticidal compounds in vegetation, which they utilize to keep their nests bug-free. Yet no bird's sense of smell is cued to human scent.
Still, there's good reason not to go fiddling around in an occupied nest. "The fact is, birds don't abandon their young in response to touch, [but] they will abandon [their offspring and their nest] in response to disturbance," explains biologist Thomas E. Martin of the University of Montana and the U.S. Geological Survey, who has handled birds from Venezuela to Tasmania without instigating abandonment. "They are likely responding to disturbance in relation to risk of harm to young."
In other words, birds, like economists, make cost-benefit decisions. If a bird has invested a lot of time and energy in hatching and rearing its young, that bird is more likely to, if possible, relocate its offspring to a new nesting site, rather than abandon them altogether when a potential predator has discovered the babies. Birds that live longer, like hawks, are more averse to risk (and more sensitive to disturbance) than short-lived birds, like robins and other songbirds. The former might abandon its young, while the latter is much less likely to do so.
The same logic applies to most animals. "In general, wild animals bond with their young and do not quickly abandon them," explains Laura Simon, field director for the Urban Wildlife Program at the Humane Society of the United States.
In fact, most creatures find extraordinary ways to ensure the survival of their young. Killdeer and ducks will feign a broken wing to lure a predator away from their babies, and raccoons and tree squirrels will speedily relocate their progeny to more protected pastures when a potential threat is skulking about.
Wild rabbits are the exception to this rule. "These animals seem to be the most sensitive to human and other smells. They're a flighty, high-stress species," Simon says. "Wild rabbits will sometimes abandon their nest when it's been very disturbed as when a lawnmower [runs it over or a] cat gets into it."
If you suspect that a rabbit's nest has been abandoned, the Humane Society recommends making an "X" out of yarn or string over the nest and checking approximately 10 hours later to see if it has been moved. If the X has been pushed aside but the nest is still covered, that's a good indication that the mother has returned, nursed her young, and then re-covered them. If the X stays in place for 12 hours after the traumatic event, it's likely that the young rabbits have been deserted.