The avian respiratory tract is an ingenious system consisting of the nares (nostrils), tracheal system, lungs, and air sacs. Inhaled air is cleansed and heated as it passes through the nares on its way to the respiratory tract. Air is then passed in a one-way, two-stage flow through the lungs. A breath of inhaled air first passes into the posterior air sacs and is forced into the lungs as it is exhaled. When the next breath is inhaled into the posterior sacs, air from the first breath is forced from the lungs into anterior air sacs. The air from the first breath is expelled from the bird during the second exhalation, while the second breath moves to the lungs. With each breath, nearly all the air in the lungs is replaced, resulting in extremely efficient gas exchange. This unique system provides continuous, unidirectional airflow delivering large amounts of oxygen and helps remove potentially lethal body heat produced during flight.
Although waterfowl have found many ways to streamline, lighten, or eliminate unnecessary structures, they have not cut corners when it comes to the nervous system. The life of waterfowl is a high-speed, aerial one. Therefore, the birds possess proportionately large brains connected to keen eyes with ample processing centers that relay and coordinate visual information. Commands from the brain are transmitted quickly via short nerves to the muscles controlling the wings and tail. This combination of acute vision, quick decision-making, and high-speed nerve transmission enables a wood duck to dip and dive through the limbs of a forested wetland with relative ease.
The body plan of waterfowl is uniquely adapted from head to toe for flight. The many adaptations waterfowl possess allow them to master the sky, traversing it in ways man can only imagine or perhaps experience in a high-performance jet fighter.
Dr. John Coluccy is manager of conservation planning at DU’s Great Lakes/Atlantic Regional Office in Ann Arbor, Michigan.