A team of researchers has found that ducklings have two separate memory banks connected to each eye. Ducklings that imprinted on a mother substitute with one eye could not recognize the decoy when that eye was covered. The findings are in a paper that was just published in the journal Animal Behaviour.
Ducklings quickly learn to recognize and follow their mother through a process called imprinting. Shortly after hatching, ducklings will imprint on the first moving animal or object they see. They will then follow this object closely, a tactic that keeps ducklings safe from harm. Ducklings are vulnerable to predators and imprinting allows the mother to lead all of her ducklings to safety without having to herd them.
Researchers from the University of Oxford hatched Pekin ducklings (Anas platyrhynchos domestica) and had them imprint on a moving decoy object. The decoy was colored either red or blue. The ducklings had been fitted with eyepatches so could only see the decoy with one eye. The researchers then switched the eyepatch to the other eye to see which decoy the ducklings preferred. Interestingly, the ducklings showed no preference between the colored decoys when they couldn’t see out of the original eye. They didn’t seem to recognize the substitutes at all. Once the eyepatch was removed, the ducklings showed a preference again.
The researchers then had ducklings imprint with one eye on the red decoy and one eye on the blue decoy, both within the sensitive imprinting period. When the eyepatch was switched from one eye to the other, the ducklings changed their preference. If the eyepatch was completely removed (allowing the ducklings to see with both eyes), they showed zero preference—showing that the information from the two eyes cancelled out.
The findings show that ducklings can store visual memory information in two different places, connected to each eye. This makes sense anatomically because birds have two brain hemispheres. In humans, these hemispheres are connected with a structure called the corpus callosum. Birds lack this structure and so information cannot jump from one side of the brain to the other—or at least not quickly. The team believes that future research could reveal how birds use this to their advantage, especially during flight.
Martinho et al. Swapping mallards: monocular imprints in ducklings are unavailable to the opposite eye. Animal Behaviour (2016).