In the summer of 2015 University of Oxford zoologists Antone Martinho III and Alex Kacelnik began quite the cute experiment—one involving ducklings and blindfolds. They wanted to see how the baby birds imprinted on their mothers depending on which eye was available. Why? Because birds lack a part of the brain humans take for granted.
Suspended between the left and right hemispheres of our brains sits the corpus callosum, a thick bundle of nerves. It acts as an information bridge, allowing the left and right sides to rapidly communicate and act as a coherent whole. Although the hemispheres of a bird's brain are not entirely separated, the animals do not enjoy the benefits of this pathway. This quirk of avian neuroanatomy sets up a natural experiment. “I was in St. James's Park in London, and I saw some ducklings with their parents in the lake,” Martinho says. “It occurred to me that we could look at the instantaneous transfer of information through imprinting.”
The researchers covered one eye of each of 64 ducklings and then presented a fake red or blue adult duck. This colored duck became “Mom,” and the ducklings followed it around. But when some of the ducklings' blindfolds were swapped so they could see out of only the other eye, they did not seem to recognize their “parent” anymore. Instead the ducklings in this situation showed equal affinity for both the red and blue ducks. It took three hours before any preferences began to emerge. Meanwhile ducklings with eyes that were each imprinted to a different duck did not show any parental preferences when allowed to use both eyes at once. The study was recently published in the journal Animal Behaviour.
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The results reveal the fundamental lack of quick communication between the left and right sides of a bird's brain—and make it apparent that information received by one eye gets transmitted to only one hemisphere. It may not seem like a good strategy to have separate records of memory in different sides of the brain, but Giorgio Vallortigara, a neuroscientist at the University of Trento in Italy who was not involved in the study, suggests that there may be an advantage to living without a corpus callosum: each hemisphere may become specialized for certain kinds of memories.
Birds normally use both eyes, allowing the two halves of their brain to work in harmony. “What this means is they are engaging in tremendous behavioral adaptations to integrate two discontinuous streams of information to make decisions,” Martinho says. “What it's like to be a bird is very different from how we might initially think of it.”