A common sight in lakes and ponds this time of year is a brood of little ducklings paddling very close to their mother.
Mother Duck’s large body moving around the nest was the first thing the newly hatched ducklings saw, and within a day’s time, they imprinted on her, meaning their brains became wired to follow that object faithfully until they mature to full independence.
There is a critical period for this type of “filial imprinting” to occur — usually within 24-48 hours of hatching. Whatever large, mobile object the hatchling sees, it follows — even if it is a human. This type of imprinting is of obvious survival value to precocial birds, those that are mobile immediately after hatching, as they learn survival skills and are protected by at least one parent.
You might wonder if imprinting only occurs in birds. The answer is NO, but there are different types of imprinting, even in birds. Social and sexual imprinting are key to making sure an individual associates with members of its own species. Keith Kendrick* cross-fostered sheep and goats immediately after birth (i.e., goats mothered the lambs and sheep mothered the kids), and found that male offspring (but not females) were subsequently irreversibly attracted both socially and sexually to their foster mom’s species more than their own.
Sort of makes you wonder about Tarzan being raised by apes…
*Kendrick et al. 1995. Mothers determine sexual preferences. Nature 395: 229-230.