Dancing in the Street

We interrupt our regularly scheduled Series to bring you this report from the field of Life Goes On.

A pair of Tufted Titmice took to the street on Gaffield Avenue,

feeling the Rhythm of Spring at the required social distance.

Nonetheless, one got Rhythm in its feet

and caught up its partner in the dance.

Spaces between the shadows came to life

as its call was answered.

Being in Rhythm is just a matter of time.

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.

Birds under Water 3 - Intrepid Divers

A series on birds at Halibut Point with diverse adaptations

to finding food below the water surface:

Dabblers, Plungers, Divers, and Pursuers.

Buffleheads, male and female

During the winter season at Halibut Point we enjoy the presence of ducks with the ability to forage for plants and small invertebrate animals on the ocean bottom. They may dive to depths of up to fifty feet. The birds that operate close to shore often find themselves in a zone of extreme turbulence, which adds to the wonder of their success.

The text for this article comes from the sportsmen's organization Ducks Unlimited. *

Bufflehead, diving

The body of a diving duck is much more compact and fusiform (wider in the middle and tapering toward the end) than that of a dabbler. Divers' wings are also more compact, which allows them to be compressed tightly against the body for greater diving efficiency. In addition, divers' legs are set much farther back on their body, and their feet are much larger and have a lobed hind toe. These adaptations help propel the birds while they are underwater.

Bufflehead diving and Harlequin observing

Harlequin Ducks

Harlequin male, diving and female, snorkeling

Diving ducks typically have higher body densities than other waterfowl. Just before they dive, the birds compress their feathers against their body, squeezing out air, which further reduces buoyancy. Next, with a single thrust of their powerful legs and feet, diving ducks arch their bodies upward and dive headlong.

Goldeneye, male and female

Goldeneye diving

Once underwater, the birds use their feet and wings to propel them downward in search of food. They steer during descent largely by shifting their head and tail positions. Once near the bottom, diving ducks use their feet to maintain a hovering position while the birds forage for aquatic insects, small mollusks, seeds, vegetation, roots, tubers, and other food.

Common Eiders

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.

Common Eider

Harlequin Duck drakes

* The text in this article is taken from "Diving Ducks: Into the Deep," by John M. Coluccy and Heather Shaw, as published on the Ducks Unlimited website www.ducks.org.

Birds under Water 2 - Plungers

A series on birds at Halibut Point with diverse adaptations

to finding food below the water surface:

Dabblers, Plungers, Divers, and Pursuers.

Belted Kingfisher scanning

Other than sharp eyes, a big beak, and a reckless constitution, it doesn't necessarily take much in the way of extraordinary avian equipment to plunge for prey below the water surface. You don't need webbed feet if swimming isn't part of the plan.

Kingfisher rising

You don't even have to be particularly waterproof for a quick strike, but the ability to get back up into the air is essential.

Ring-billed Gull hovering

Most of our larger gulls are too buoyant in the water and heavy-bodied in the air to plunge below the surface as effectively as the Ring-bill.

When small fish appear near the surface this species is capable of going after them.

Migrating juvenile fish driven into the shallows by predators make a perfect opportunity for a moderate plunger.

Minnows schooling near the quarry surface are fair game for Ring-bills. Great Black-backed and Herring Gulls lack the quickness for this technique.

Northern Gannet

Gannets are the most highly adapted of the maritime plungers in our area. They soar high enough to see well below the surface of the ocean.

When striking they tuck into an aerodynamic posture for speed and fine ballistic steering. Just before hitting the surface they tighten into an arrow to penetrate the water to the fish's depth.

Their foreparts are reinforced to withstand impact. Unlike gulls, the design of their legs and feet enables them to chase fish under water.

After a successful dive a gannet may have to swallow his prey quickly at the surface before a gull can arrive to do what gulls do best. Even-handed biologists call the gull's way of making a living kleptoparasitism, a fancy term for stealing, but less invasive than lodging inside and digesting a host's internal organs.

Then the honest predator lifts off the water to fly in search of another meal.

Birds under Water 1 - Dabblers

A series on birds at Halibut Point with diverse adaptations

to finding food below the water surface:

Dabblers, Plungers, Divers, and Pursuers.

Brant in Folly Cove

Considering the abundance of life in the waters of the earth, it should not be surprising that birds have sought out its food potential. 

Brant eating sea lettuce

From their origins as creatures of the land and the air some species have developed anatomy and lifestyles to harvest sustenance from aqueous environments.

Dabbling Mallards

Beyond wading in search for food, a significant variety of birds have enhanced their waterproofing, foot and bill structures to swim on the water surface and reach below in search of food sources.

American Wigeon (top) with a Mallard pair

Mallard ducks are the commonest and emblematic local dabblers. Searching among Mallards may reveal cohabitating species.

Female Mallard with Green-winged Teal

The dabblers are generally found in shallow water. They tend to have a rounder shape and float more buoyantly than waterfowl that rely on diving for food.

Warm Bodies

Colorful barelegged creatures with the gifts of flight and song are surely a great marvel of the winter landscape.

Red-winged Blackbird

Their concerts are not cancelled by irregular weather. To be sure of its melodies Nature must keep songbirds warm.

Tree Swallows during spring snowstorm

Photo courtesy of Keith Williams/Creative Commons

Huddling birds can share their warmth, reduce exposure to cold air, and shield each other from wind.

Brant

The hard work of flight generates more than enough heat for a comfortable body temperature while a bird is active.

Robin

At rest they are likely to fluff their feathers and wrap themselves in their wings as advantageously as possible.

Snowy Owl

Snowy Owls even have feathered feet.

Common Eider

Eiders, one of our winter coastal ducks, have some of the most effective insulation of any bird. Their perfectly interlocked outer feathers form a 'barrel'  to trap pockets of air around their bodies even when diving. The birds waterproof this guard layer by using their bills to coat it with oil from a preening gland near the base of their tails. Eiders are also the source of down feathers utilized in superior winter clothing and bed comforters.

Varieties of feathers

Illustration from The Birdwatcher's Companion by Chris Leahy

Intricate combinations of feather structures beneath the outer layer keep the bird warm as well as streamlined for flight.

Mourning Dove

A few species of birds like egrets, herons and mourning doves grow special feathers that disintegrate into a powder they use to waterproof their feathers.

Black-capped Chickadee

Chickadees weighing less than half an ounce can maintain a daytime body temperature of 100 degrees Fahrenheit by having great insulation, being very active and remembering where they store their food. They eat more than a third of their weight every day. Compared to many other birds, chickadees have a large hippocampus - the part of the brain that’s responsible for spatial memory. In the fall, this part of their brain gets even bigger!

These small creatures can't put on too much bulk for aerodynamic reasons. Instead, they are experts at shivering. Birds activate opposing muscle groups to create contractions without all the familiar trembling that mammals use to generate heat. At night, tucked into a tree cavity, they might reduce their body temperature as much as 22 degrees from their daytime level in a process called regulated hypothermia.

Chickadee foot temperature is regulated near the freezing point and may stay cold most of the time all winter, even as core body temperature stays high. Of course, a bird’s comfort level for foot temperature is likely very different from ours. They would not feel uncomfortable until the point when damage occurs from freezing, if ice crystals were to form.

Online information on Chickadees
1. U. S. Fish & Wildlife Service Newsroom, "How do birds keep warm in the winter?"
2. Audubon.org, "How Do Birds Cope with Cold in Winter?"
3. Cornell Lab All About Birds, "How Do Birds Survive the Winter?"