FEATURE
A Double Yellow-headed Amazon parrot, showing ‘pinning’ of its pupil, elevation of feathers on its neck and its wings, and spreading of its tail feathers, all controlled by voluntary muscle contraction, and in this case demonstrating a threat display.
Photo © Dr Jan Hooimeier
damaged, unlike those of humans which cannot, leading to permanent loss of hearing. The apparently simple syrinx at the base of the windpipe is the organ of voice production. This contains two separate membranes, each with their own neural connections, allowing the production of two separate, simultaneous sounds. Humans utilise just 2% of the air passing through the larynx for sound production, whereas parrots are able to make use of 100% of the airflow. Now wonder their ear-splitting vocalisations may be heard for miles! The powerful and characteristic hooked beak of parrots is well supplied with nerve
endings sensitive to pressure, touch, texture, resilience, temperature and pain. Both upper and lower portions of the beak articulate separately against the skull, and they grow continuously throughout life. Parrots’ body temperature is higher than humans, at 104°F (40°C), allowing nerve impulses to travel faster and muscle action to be stronger, once again aiding explosive flight and fast reactions. The disadvantage is that energy expenditure is high. Heat may be generated by shivering the pectoral muscles, and the body feathers make a very efficient insulating layer to retain body heat. Conversely, parrots seek out shade and are inactive in the heat of midday. The
BIRD SCENE 33
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