-- Brat11@sev.org

IN MOST ANIMALS, the pupil, the black opening in the middle of the iris, changes size for a number of reasons. For one, pupil size controls the amount of light that can enter the eye. Changes in pupil size can also signal a change in blood pressure or an emotion such as fear, aggression, or excitement. Changes in pupil size even have been recorded during the processing of new information. In mammals such as humans, these changes are involuntary. A signal comes from a nerve in the brain and travels to the eye, telling the muscular iris to open or close the pupil.

Birds' pupils change in size for all the same reasons as humans' do. However, they also enjoy conscious control over the iris and other eye muscles. According to avian veterinarian Dr. Susan Orosz, the signals sent from the brain to a birds' eyes travel from some of the same nerves as in mammals, but they take a different path that allows the bird discretion over the results. In addition, a bird's eye muscles are different from ours - they are more like the muscles in our arms and legs. As a result, birds can control how and when the muscles in their eyes move, and make their pupils small or large whenever they want or need to.

This type of control is what allows a falcon traveling at over 200 mph to instantaneously change focus from a faraway object to one that is near, or vice versa. If we tried to do that we’d probably fly into something! That same control allows a parrot to use his eyes to convey that he is feeling afraid, aggressive or interested. By constricting, or "pinning," and opening, or "flashing," his pupils while he is talking, your bird is letting you know just how excited he is at that moment.

Emily Insalaco is a trainer with Steve Martin's Natural Encounters, Inc., an international consulting group that helps zoos train birds and other types of animals using positive reinforcement.

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