by Rebecca Senft
figures by Michael Gerhardt and Rebecca Senft
If you’ve ever seen a long line of ducklings waddling across a road, you know that they follow their mother dutifully, even in the face of oncoming traffic. Ducklings, like many species of birds whose young leave the nest early, are able to identify their own mother and siblings based on sight and won’t follow other mothers or siblings. This ability to recognize and follow their family greatly reduces the chance that ducklings will wander off into danger.
How do ducklings know to follow their mother and siblings? The roots of this behavior remain a mystery that has fascinated researchers, for they show that birds have cognitive abilities that do not need to be learned. Intriguingly, a study published just this past summer has taken this research one step farther and found that ducklings may be even smarter than we imagined. Researchers found that ducklings can demonstrate abstract thought, or the ability to understand more than just what they can see. These breakthroughs on duckling cognition may even contribute to our understanding of our own brains and how humans came to become good at thinking.
Imprinting: how ducklings recognize and learn to trust their mothers (and siblings)
In the first days of life, during what is called a ‘sensitive period,’ young birds of many species undergo a phenomenon called imprinting (Figure 1). During a young duckling’s imprinting, images of the duckling’s mother (and its siblings) act like a metaphorical stamp, leaving an impression in the brain that guides the young duckling on who to follow. Outside of the sensitive period, this bond will fail to form. Though it often works out that the mother is the first thing the duckling sees, this doesn’t have to be the case. In fact, if a duckling is separated from their mother right after birth, it’s possible that they grow up following whatever moves around them during this time. This abnormal imprinting behavior was described in detail by Konrad Lorenz, an Austrian biologist whose work studying imprinting in geese ultimately won him the Nobel Prize in 1973. He discovered that young goslings would not only follow him around, but also red balls, blocks, or any noticeable moving object. The requirement of movement and visual contrast lead to the belief that ducklings primarily use sight to imprint and follow their mother. However, the science behind imprinting has changed a lot since the 1970s.
Recent revelations on imprinting
Research from the 1980s onward has demonstrated that imprinting is far more common than Lorenz imagined. For example, from work done in baby chicks, we now know that the richness of a young bird’s environment can affect how well birds imprint—for instance, classical music has been shown to improve the strength of a bird’s imprinting. Imprinting also isn’t purely visual; young chicks can imprint on sounds, like a mother hen’s cluck. Young birds can even generalize from an imprinted object to follow other, visually similar objects. For example, chicks allowed to imprint on red cubes more readily followed blue cubes than blue cylinders. This latter research raised the question of how far young birds can generalize. How much do they understand about the objects or animals they imprint upon? If given a pair of objects, could ducklings recognize whether the objects are the same or different? And could they generalize this knowledge to new object pairs? If ducklings could recognize two objects as identical (or different) and apply this knowledge to new objects, this would strongly imply that ducklings are capable of abstract thought—that they can understand more than just the colors and shapes they see in front of them.
These exact questions were explored by scientists Antone Martinho III and Alex Kacelnikand colorful shapes. In a paper they published in July of 2016, they found that in fact, ducklings were smart enough to understand the abstract concepts of “same” and “different.” Instead of relying only on visual information (e.g. color and shape) to follow an imprinted target, ducklings could understand abstract relationships between objects. This research made a huge splash in the world of animal learning because prior to this, the ability for abstract thought was only demonstrated in some non-duck birds and primates after extensive training. However, ducklings were able to learn these abstract relationships with only one exposure to an imprinting pair.
Testing ducklings for abstract thought
Ducklings were allowed to imprint on a pair of objects that moved around a circular arena (Figure 2). The pair of objects could be either identical (e.g., two red balls) or different (e.g., one red ball and one blue). They were then given two new pairs of objects they had never seen before. The pairs didn’t look anything like what the duckling imprinted on, but one pair demonstrated the same relationship (e.g. same color) whereas the other had the opposite relationship.
Given no one had demonstrated abstract thought in ducklings before, researchers found that, somewhat surprisingly, ducklings consistently followed pairs that had the same relationship. In other words, if the first imprinting pair was two differently colored objects, ducklings preferred second test pairs that included two differently colored objects to those that had two same-color objects). This occurred even though the testing pair they chose bore no superficial resemblance to their imprinting pair. This means that when ducklings initially imprinted, they were able to understand their first object pair on more than just raw appearance—thus, at a deeper level than previously known by scientists.
Because ducklings, unlike primates, don’t have to be trained with rewards or punishment to understand these concepts, this suggests that an innate understanding of the difference between ‘same’ and ‘different’ may be very important for survival and thus, may be an ability ‘hard-wired’ into ducklings by evolution. If ducklings can understand and imprint on their mother not just as a single image, but as a set of objects that go together (e.g., two eyes that move together next to a beak) they will be more likely to recognize their mother, even from different angles and under different lighting conditions, when the visual information the duckling receives varies greatly. Another interpretation of this research is that abstract thought isn’t actually a very complex or difficult ability, but rather one shared by many animals. By studying more species and the underlying mechanism behind abstract thought, we can begin to piece together whether abstract reasoning is necessary and foundational for many species or a more exclusive ability, as previously thought.
The future of imprinting research
Abstract thought isn’t just studied in ducklings. Research subjects range from birds to primates to human infants, with much of this research aiming to understand how abstract thought has evolved and been elaborated on over evolutionary time. Though animals like ducklings lack the full spectrum of cognitive abilities seen in humans, studying their cognition can teach us a lot about how reasoning abilities evolve. Human research on infants has demonstrated that by 7 months old, human babies can distinguish pairs of identical objects from pairs of different objects, much like the ducklings in the study described here. However, newborn ducks are actually far better at this kind of abstract discrimination task, requiring only one pair of objects to understand compared to the four example pairs required by human babies.
Future research can look at how ducklings are able to make these distinctions between same and different. For example, which brain regions are active during imprinting that could be responsible for decoding relationships between objects? Can adult ducks also learn as readily as ducklings, or understanding abstract relationships a feature of the sensitive period of imprinting? There are still many questions remaining in the fields of abstract thought and animal learning, but by studying the abilities of ducklings and other animals, we may begin to emerge with a better understanding of how we evolved to be so good at abstract thinking. From what we see of newborn humans, we may not have much to separate us from ducklings.
Rebecca Senft is a Ph.D. student in the Program in Neuroscience at Harvard Medical School.
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