Birds fascinate us in many ways, from their colorful plumage and intricate songs to their amazing courtship displays, varied diets, and stunning species diversity. Nothing is more fascinating, however, than a bird's ability to slip from earth's gravity and soar into the clouds. But how do birds fly, and how can understanding the activity that comes so easily to our feathered friends help us be better birders?
Why Flight Fascinates Us
Birds seem to fly effortlessly, yet no matter how much a human may flap their arms, they cannot replicate that simple action. Birds have been flying for millions of years, and young chicks may start flying just a week or two after hatching, depending on the species. Many birds make miraculous migrations, and other species have amazing aerobatics in their flight patterns. Some birds, such as kingfishers and hummingbirds, can hover with ease, while other birds, such as peregrine falcons and ospreys, have spectacular hunting dives. Birds can maneuver through tight passages, or even dodge to avoid obstacles on the wing. With so much variety in flight, there is always something new to discover about this aerial ability, and more to fascinate us.
Birds migrate out of an instinctive restlessness—which sets in as the length of days and angle of the sun change—and they will naturally touch down wherever food resources are plentiful.
The Physics of Bird Flight
There are many factors that go into a bird's ability to fly. Physical characteristics, behavior, and local air conditions all help define how birds fly, including:
- Wing Shape
A bird's wing is thicker at the front than at the back, and more curved across the top than underneath. This causes air to move more quickly over the longer surface of the upper wing than the shorter surface below the wing. This disparity in airspeed above and below the wing causes lower air pressure on top and stronger pressure below, which is the lift that raises the wing and propels the bird higher.
- Wing Motion
As a bird flaps, its wing subtly twists to take advantage of wing shape and create more thrust to propel the bird forward and up into the air. This pushes the bird through the air, similar to how a swimmer will push through the water with every stroke as they change the position of their shoulders, hands, and arms.
- Body Structure
A bird's entire body is built to help it fly. Bird skeletons are a lattice-like structure or honeycomb shape filled with air hollows, reducing the overall weight of the bird. Fewer redundant organs, such as a single ovary rather than a pair, also reduce a bird's weight so it can fly more easily. Larger chest muscles give more power to a bird's wings for stronger flight.
- Body Activities
The internal workings of a bird's body also help it fly more efficiently. A bird's body temperature is higher to permit muscles to work more quickly, and both the circulatory and respiratory systems operate more efficiently to support the massive effort required to fly. Birds also have higher metabolic rates so they can digest food more quickly to turn it into energy for flight.
A bird's feathers are more than just a colorful covering for its body. Each feather is aerodynamically shaped and precisely positioned to assist flight by adjusting airflow over and around the bird's wings and body. Birds can adjust some key feathers to help steer through the air, and tail feathers are often used as a rudder for broad movements.
- Streamlined Shape
Birds' streamlined shapes help make flight easier by reducing drag and friction in the air. The tapered point of a bird's bill slices through the air, and the smooth curves of the bird's body guide the air around their bulk with as little resistance as possible. Birds even tuck their legs and feet up while flying to reduce drag even further.
- Leg Power
Some birds use their powerful legs to assist their flight by providing the initial thrust needed to get into the air. For many birds, this is from a first leap as the bird jumps into flight. Similarly, many waterfowl use their strong legs and webbed feet to build up speed across the surface of the water as they take off into flight.
- Air Conditions
Not only are birds spectacularly equipped to be efficient fliers, but they also take advantage of air conditions for more efficient flight. Air currents, wind, and air temperature differences all contribute to flight dynamics and help birds fly. Birds can sense subtle air changes with their sensitive skin, and will change their flight behavior to fly more easily in different air conditions.
Using Flight to Be a Better Birder
The more we understand about how birds fly, the better birders we become. We can:
- Learn to identify birds in flight by recognizing flight patterns, wing shapes, and other characteristics that are unique to each bird's type of flight.
- Provide more nutritious, healthy food for birds to fuel their flights, particularly during peak migration seasons when birds are flying long distances in short periods and natural foods may be scarce.
- Conserve safe, suitable habitats along migration flyways to provide birds with resting areas along the top migration routes, especially for critical species.
- Minimize hazards that threaten bird flight, such as oil spills that destroy feathers or accidents that amputate legs and inhibit birds' abilities.
Flight has fascinated birders for millennia. As we learn more and more about the intricacies involved in avian flight and how we can be a part of it, flying will continue to fascinate us, even while we stay on the ground.