Imprinting: Why Ducklings Follow the First Thing They See

The image is famous: a line of goslings trailing a man in wellington boots through a meadow. What that photograph actually demonstrates is a form of early learning called imprinting, and almost every popular account of it gets at least one detail wrong — including the part about it being permanent, and the part about there being a tidy window of a few hours after hatching.

Lorenz named it, but he was not first

Konrad Lorenz revealed in the 1930s, as the Nobel Foundation’s own summary puts it, that “birds hatched in an incubator without the presence of their parents follow whatever they first catch sight of. For example, they can become fixated on a person.” He called the phenomenon Prägung — stamping — and described it as a special kind of learning that needed no reward and could not be undone.

He shared the 1973 Nobel Prize in Physiology or Medicine with Karl von Frisch and Nikolaas Tinbergen, one third each, “for their discoveries concerning organization and elicitation of individual and social behaviour patterns.”

But a 2024 systematic review in Ethology records that behavioural imprinting entered the scientific literature in 1873, when Douglas Spalding described what he took to be an innate instinct in young domestic chicks to follow the first moving object. Lorenz named it and made it famous sixty years later; Spalding saw it first.

The window: there isn’t a single number, and anyone who gives you one is simplifying

This is where most accounts go wrong. You will frequently read that a duckling imprints in the first 13 to 16 hours after hatching. That figure has a real source, but it has been overtaken.

The classic result, reported through a major review of avian imprinting in Biological Reviews, is Hess’s 1959 work on ducklings: responsiveness rose after hatching until about 15 hours, then declined until, by 30 hours, the proportion of positive responses was near zero. That is the origin of the number everyone quotes.

Then the picture complicated. The same review reports Smith and Nott finding in 1970 that an audiovisual imprinting stimulus could still induce following in domestic chicks up to 10 days after hatching, with the following response persisting to at least day 28. The review’s own conclusion is that the sensitive period “is not as circumscribed as has been thought previously.”

And for ducks specifically there is a further twist. A 2019 review in Frontiers in Physiology notes that Gottlieb found duckling sensitivity was strongly associated with time since the start of embryonic development — not time since hatching. In other words, the clock a duckling is running on started when the egg started developing, which is why any figure expressed as “hours after hatch” is approximate at best. That review describes the sensitive period as typically lasting several days but “very variable in duration.”

The honest summary: classic work put the duckling peak around 15 hours with responsiveness fading by 30; later work found much longer windows in chicks; and in ducks the timing appears to track developmental age from the beginning of incubation. If you are incubating duck eggs, that last point is the one that matters.

What a duckling is actually responding to

Not simply “the first thing it sees.” The Biological Reviews survey identifies several properties that make an object a more effective imprinting stimulus. Movement increases attractiveness. Pairing sound with the visual stimulus makes it more effective than vision alone. Colour matters — red and blue were found to work better than yellow and green. And in general, the more conspicuous an object is to the human eye, the more effective it is.

Work on chicks adds that motion cues support object perception and that naïve chicks show an innate preference for biologically plausible movement patterns. There is also a separate innate predisposition, distinct from imprinting itself, which can be switched on by mild non-specific stimulation — handling, exposure to white light, or a hen’s maternal call.

The part that happens before hatching — and it is not what you would guess

Ducklings call inside the egg before they hatch, and the mother calls to them. The obvious assumption is that the duckling learns its mother’s voice through the shell. The evidence points somewhere more surprising.

The Frontiers in Physiology review, reporting Gottlieb’s work, states that a duckling’s post-hatch ability to acquire a preference for the adult maternal call of its own species “requires previous experience of embryonic contact-calls in the egg” — that is, the duckling needs to have heard its own and its siblings’ calls. Hearing itself is the prerequisite for later recognising its mother. The same work found that ducklings reared in isolation could not imprint on a non-species call at all, and only did so when they had tactile contact during social rearing.

Ducks Unlimited describes the same window from the nest side: two days before hatching the young can hear the hen’s call and begin making their own vocalisations, and it is this communication among unhatched siblings that lets a clutch hatch in synchrony. Anyone who has watched a broody duck sitting tight through the final days is watching that conversation happen.

Can ducklings imprint on an idea?

In 2016, a paper in Science by Antone Martinho and Alex Kacelnik reported that newly hatched mallard ducklings could imprint not on an object but on a relationship — whether a pair of objects was the same or different. Ducklings were shown a moving pair of objects for 25 minutes, kept in darkness for 30 minutes, then given a ten-minute choice between two novel pairs. Across both experiments, 77 of 113 ducklings — 68% — preferred the pair showing the relationship they had been exposed to.

It was widely reported, and it is worth knowing two things about it. First, the University of Oxford press release said “approximately three-quarters” of ducklings; the paper says 68%. Use the paper’s figure.

Second, the result has been formally challenged. A 2017 Comment in Science by Jean-Michel Hupé argued the statistics are fragile: different but defensible analyses of the same data give P-values ranging from 0.0001 to 0.37, and with a Bonferroni correction the combined data yields P = 0.18. Other researchers have written supportively, describing the rapid learning as far outstripping the more gradual concept learning seen in other species. The finding is interesting and it is contested, and a duck site that tells you only the first half is not being straight with you.

Is it permanent?

Lorenz said it was irreversible. That turns out to be wrong, at least under laboratory conditions.

The Biological Reviews survey reports work by Salzen and Meyer in which chicks imprinted on a coloured ball, then had it replaced with an alternative for three days, and reversed their preference to the new object. The Frontiers review concurs that a completed imprint can later be reversed by prolonged exposure to a second object. But there is an important qualification: “filial preferences are reversible, but that does not mean that information about the first object is forgotten.” The preference changes; the memory stays. Most of this evidence comes from chicks rather than ducklings.

Why this matters if you find a duckling

The practical consequence is the least ambiguous part of the whole subject, and it is serious.

Washington Department of Fish and Wildlife’s Wildlife Rehabilitation Manual defines imprinting as happening “in very young animals at a precise critical period where the animal fixes its attention on and follows the first object or creature it sees, hears, or touches,” and spells out the consequence of getting it wrong: “If the animal imprints upon you, it will believe it is supposed to follow you and do what you do resulting in the animal not recognizing its own species and preventing its release.” The manual’s conclusion is stated without hedging: “Tamed, habituated and human-imprinted, or mal-imprinted, animals cannot be released; they will not survive in the wild.”

Professional rehabilitators work around this deliberately — raising ducklings with siblings of their own species, or using a bird-skin puppet rather than a bare hand. A hand-reared wild duckling that decides you are its parent is not a charming story. It is a bird that has lost the ability to go home.

For domestic ducklings the stakes are different but the mechanism is identical, and it is worth knowing before you start raising ducklings week by week: the first days shape what your birds think they are, and they are paying attention long before you think they are.