Birds under Water 4 - Deep Divers

A series on birds at Halibut Point 

with diverse adaptations

to finding food below the water surface:

Dabblers, Plungers, Divers, and Pursuers.

Ring-necked Ducks

Occasionally fresh-water birds like the Ring-necked Duck that normally dive for plants and seeds in shallow lakes, stop for a rest along this coastline. The Halibut Point environment challenges them in many ways.

Greater Scaup

A bird like the Greater Scaup is an unusual visitor from the muddy-bottomed salt water bays where it can find food such as clams and plants.

Three scoter species in flight

The deeper-diving sea ducks have had to evolve a balance between lightness for flight and heavy musculature to reach the ocean bottom in search of food. They are buoyant enough to float and stay warm in their 'default' resting state with the least counter-acting effort to 'corkiness' in swimming under water.

Black Scoters, male and female

Notice how much lower these sea ducks sit in the water than the two species above. By compressing their feathers they become less buoyant in preparing to dive.

White-winged Scoters, male and female

Diving creates a problem for birds: They need a continuous supply of oxygen and must get rid of carbon dioxide, but diving requires breathing to stop. For starters, divers have greater blood volume and store more oxygen, as oxyhemoglobin in blood and oxymyoglobin in muscle, than non-divers. Tufted Ducks, for example, have 70 percent more oxygen per kilogram of body weight than Mallards. ¹

Surf Scoters, 2 males and a female

These birds are sitting higher in the water than the Black Scoters pictured above. They have achieved resting buoyancy and insulation by fluffing their inner feathers, incorporating air within their down beneath the guard feathers.

Birds that are foot-propelled in water generally hold their wings tightly while diving and swimming, so as to streamline the body. Eider and scoter ducks, however, keep their wings partially extended to help in propulsion and maneuvering. ²

King Eider

Carbon-dioxide buildup stimulates birds to breathe and can ultimately force breathing — death for a diver. To counter this problem, divers have a better buffering system that allows them to accumulate more carbon dioxide before breathing. ¹

Long-tailed Ducks, 2 males and a female

About six seconds into a dive, a reflex causes general metabolism to decrease. The heart rate slows by about 50 percent, and blood is shunted from the skin, viscera, and musculature — body parts that can tolerate limited oxygen — to the heart and brain, which require a constant supply. The actions help conserve a limited oxygen supply. If required, rapid muscular activity can be accomplished anaerobically. Lactic acid that builds up will be removed metabolically after oxygen is restored. ¹

Long-tailed Duck preparing to dive

Long-tailed ducks are the deepest divers in the duck family, reportedly capable of reaching depths of 200 feet. Their bodies are more streamlined than scoters and to a greater extent able to use their wings for propulsion, to some degree “flying underwater” in the manner of penguins. ³

Sources
1. Eldon Greij, "How Birds Are Able to Dive and Swim Below the Waves," www.birdwatchingdaily, October 4, 2018.
2. Paul R. Ehrlich, David S. Dobkin, and Darryl Wheye,
web.stanford.edu/group/stanfordbirds/text/essays/Swimming, 1988.
3. Chris Leahy, The Birdwatcher's Companion, 2004.