Archaeopteryx, a bird ancestor known as the first feathered creature to take flight.
Photo: John Sibbick/Q-files
Look! Up in the Sky! It’s a Flying Dinosaur!
By Kevin McKeon, Maine Master Naturalist
A coastal wading bird called a bar-tailed godwit began its annual migration flight from Alaska, landing in Tasmania, Australia 11 days and one hour later, after 8,435 non-stop miles. An Arctic tern flew almost 60,000 miles on its round-trip journey between England and Antarctica. A Rüppell’s griffon vulture collided with a plane flying seven miles high — almost 1 ½ miles higher then Mt. Everest. And a common swift managed to stay aloft non-stop for 314 days — over 10 months! How do they do it?
Birds fly by gliding, soaring, flapping, hovering, and assisted bounding. They do this to forage and feed, to migrate, as a display for mating, and to avoid predation. Bird flight began its evolutionary journey during the Jurassic period, when Earth’s super-continent Pangea began to fracture into our present-day continents, modern fish were developing, and the giant dinosaurs ruled. Among them were the theropods — reptiles that walked on hind legs with very short front legs/arms, and with feet not unlike modern birds’ claws and talons. (T. Rex was a theropod.).
Pterosaurs, a reptile with skinned wings, is generally considered the first animal to take to the skies, about 200 million years ago. But 50 million years later, on a particular raven-sized theropod, feathers began their evolutionary growth as hairs that formed branch-like protrusions, giving this dinosaur coloring and insulation. It began short hopping and gliding flights as its forelimbs evolved into wings. It was called Archaeopteryx — “ancient wing”; studies of their 150-million-year-old fossils indicate they were probably the first feathered creature to fly. Flight evolution proved to be quite fortuitous, as flying dinosaurs are thought to be the only dinosaurs that survived the mass extinction event caused by the huge asteroid/Earth collision 66 million years ago. Ornithologists generally agree that today’s birds are actual living dinosaurs, direct descendants of theropods, as evidenced by their reptilian feet, claws, talons, egg-laying — and Archaeopteryx fossils.
Birds eventually became highly specialized for flight, with different species evolving wing shapes and body types to perform various types of flight to suit their environments and needs. These specialized anatomical features are found in birds’ skeletal, muscular, respiratory, digestive, and circulatory systems — and of course, in their feathers. So, scientists have decided to define birds as animals that display certain characteristics: Feathers, hard-shelled eggs. four-chambered heart, beaked and toothless jaws, lightweight skeletons, high metabolic rate, and wings. Nope, flight isn’t one of ‘em. Penguins and ostriches are among about 60 flightless birds. But this is about bird flight, so…
Optimizing flight requires maximizing the strength-to-weight ratio, so birds have developed air-filled, aerodynamically shaped, flattened, light-weight bones for flight, reinforced and fused together with struts and trusses for the rigidity to support the rigors of flight. The birds’ large sternum (breastbone) is keel-shaped to both reduce wind drag and increase strength to withstand the stresses of both flight and muscle-use from the attached large breast flight muscles. And birds’ muscles can re-shape during flight to mitigate air resistance.
Birds’ unique breathing is the most efficient in the animal kingdom, using lungs that don’t expand and bellows-like air sacs. Two breathing cycles are needed to complete one breath. Air from the first inhale passes through nostrils and into posterior (rump area) air sacs. At the first exhale, air is not expelled from the body — it gets pumped from the rump air sacs into the lungs, where oxygen is absorbed and carbon dioxide released. The second inhale moves stale air from the lungs to different, anterior air sacs located near the lungs; then the second exhale pumps the stale air from the anterior sacs through the nostrils and out the body. All this enables a unidirectional air flow through lungs, air sacs, and bones — keeping fresh air separated from used air, enabling almost 100% oxygen-use efficiency. (Humans have about 25% efficiency.)
So now the oxygenated air has entered the bloodstream via the lungs, and it’s time for the bird’s heart to pump it around. Our bird needs lots of oxygen for flight, so two things have evolved: A special heart and hemoglobin-rich blood. Our bird’s heart has muscle fibers a third to a tenth the size of our mammalian heart fibers; this results in a high ratio of muscle-surface-area to volume, which enables a faster heartbeat under much higher blood pressures. Hemoglobin in blood absorbs oxygen, and our birds have a lot of it, creating highly oxygenated blood. So, an oxygen-rich blood under greater flow and pressure enables very high respiration efficiencies and metabolic rates, enabling sustained, long flights at high altitudes, and supporting the typical high energy activities of our birds.
Feathers are birds’ most noticeable feature, providing insulation, waterproofing, color, camouflage, mating display, flight, and flight control. Made from beta-keratin, they’re stronger than the alpha-keratin in our hair and fingernails. Individual feather filaments mesh using barbs, forming a strong, continuous, and very smooth surface that air efficiently flows over but cannot readily penetrate. During flight, the upbeat of wings twists the feathers, allowing air to pass; the downbeat then flips the wings back into position to push against the air. The U.S. Fish & Wildlife Service has a nice feather illustration page here. and for a much deeper dive, visit Cornell Lab’s All About Feathers page.
Feather illustration: https://www.fws.gov/lab/featheratlas/glossary.php
Cornell Lab page: https://academy.allaboutbirds.org/feathers-article/
Editor’s note: Did you see something unusual last time you were out in the woods? Were you puzzled or surprised by something you saw? Ask our “Out in the Woods” columnist Kevin McKeon. He’ll be happy to investigate and try to answer your questions. Email him directly at: kpm@metrocast.net
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