As you might expect, diving ducks carry large volumes of air with them when they dive. For example, the respiratory system of lesser scaup is estimated to account for 52 percent of their initial buoyancy. Like other specialized diving birds, diving ducks also have an unusually high tolerance for asphyxia, or lack of air. In fact, diving ducks reduce their oxygen consumption while they are underwater. During a dive, available oxygen is rationed sparingly to sensitive tissues in the central nervous system and sensory organs. In addition, the heart rate is reduced, and blood flow to most other organs and skeletal muscles is curtailed. At these times, organs and tissues rely on anaerobic (oxygen-free) metabolism. This “diving reflex” is triggered when water touches special receptors in the birds’ nares (nostrils).
When the dive is complete, diving ducks simply relax their muscles, stop paddling, and ascend to the surface like a cork. Diving ducks that feed on submersed aquatic vegetation or sedentary invertebrates like clams return to the surface in almost the same place. But birds feeding on mobile prey like amphipods or fish may surface more than 50 feet from the initial dive location. Following each dive, the birds take a short rest break of 10-30 seconds before diving again. In one study, a white-winged scoter spent an average of 58 seconds underwater during each of six consecutive dives and rested for an average of 12 seconds between dives.
Diving ducks possess many specialized adaptations that make them uniquely suited to exploit deep-water habitats. Unfortunately, much of this habitat has been lost or severely degraded across North America. The good news is that Ducks Unlimited is working hard with many partners to conserve these habitats and secure a brighter future for these magnificent birds.
Dr. John Coluccy is manager of conservation planning and Heather Shaw is a conservation specialist at DU's Great Lakes/Atlantic Regional Office in Ann Arbor, Mich.