Flight in Nature: Bird & Insect Flight – EVERYTHING YOU NEED TO KNOW!!!! Feathers and flight A bird is designed for flight. The combination of light weight, strength and shape, as well as precision control, is largely responsible for giving birds their special ability for sustained flight. Every part gives maximum power with a minimum of weight. The heavier the animal, the bigger its wings need to be. The bigger the wings, the more muscle is needed to move them. Birds’ feathers are essential for flight. Birds’ feathers are light, strong and flexible Birds’ feathers are designed to be light but very strong, flexible but very tough. Although it looks like feathers grow all over a bird, they actually grow in specific areas called feather tracks. In between the feather tracks are down feathers. This keeps the body weight down. Feathers are made of a tough and flexible material called keratin. The spine down the middle, called the shaft, is hollow. The vanes are on the two halves of the feather. They are made of thousands of branches called barbs. Because there are many spaces between these barbs, a feather has as much air as matter. Contour feathers The contour feathers of a bird are the outside feathers – the ones that you can see. They provide the colour and the shape of the bird. The contour feathers tend to overlap each other, much like tiles on a roof. The feathers tend to shed rain, keeping the body dry and well insulated. Each contour feather can be controlled by a set of specialised muscles, which controls the position of the feathers, allowing the bird to keep the feathers in a smooth and neat condition. The smooth and streamlined surface is achieved because the feathers’ barbs are joined together with barbules (branches on the barbs). The barbules have hooks that lock the barbs together. If the barbules are disrupted, the bird passes its bill though the feather to link them again. The contour feathers used for flight are known as remiges (wing feathers) and rectrices (tail feathers). Remiges (wing flight feathers) These feathers are strong and stiff, supporting the bird during flight. They can be divided into three groups: • Primary feathers: These are the largest of the flight feathers and propel the bird through the air. They are the farthest away from the body, attached to the skin of the wing on the ‘hand’ of the bird. In most bird species, there are 10 primary feathers on each wing. If these flight feathers are damaged or lost, a bird cannot fly. • Secondary feathers: These run along the ‘arm’ of the wing and sustain the bird in the air, giving it lift. The number of secondary feathers varies with different species. Experiments have shown that, if half of the secondaries are removed, a bird will still be able to fly, but some control will be lost. • Tertiary feathers: These are on the ‘upper arm’ of the bird. They are the short, innermost flight feathers on the rear edge of a wing, close to the body of the bird. They are not as important for flight as the primary and secondary feathers. Rectrices (tail flight feathers) The rectrices or tail flight feathers are mainly concerned with stability and control. They are used as a rudder, helping to steer and balance the bird and allow the bird to twist and turn in flight. These feathers also act as a brake for landing. Coverts Bordering and overlaying the edges of the remiges and the rectrices are rows of feathers called coverts. These help streamline the shape of the wings and tail (minimising drag) while providing the bird with insulation. Angle of Attack: An important aspect of lift is the angle of attack (defined as the angle the wing is to the oncoming air force). At a certain angle of attack the bird will stall and fall. This happens with planes if they try to fly up to fast- they stall. What is the critical angle of attack anyhow? This is a tricky questions because it depends a lot on airspeed. It also depends on the type of wing a bird has. For instance, certain birds that fly at low speeds, like vultures, have different types of wings with slits in them that allow them to break up turbulence and gain lift. (Birds also have an alula, or a mid wing slot that allows them to fly at different speeds - similar to the flaps on an airplane wing). THRUST: While lift is always an issue for birds, we have yet to talk about thrust, or the act of moving the bird forward. Just flapping a wing up and down isn't going to move it forward, just up. For birds, their solution comes from the unique rotation of their wings. As the wings beat, the primary flight feathers actually twist to provide thrust. This twist is partly a result of asymmetrical veining of the feathers. Types of Wings • High Aspect Ratio Wing: • a. Much longer than it is wide. Has lot of vertical lifting area. Not much slotting. • b. Not fast flying birds but more soaring birds • c. Albatross, or Frigate bird. • Elliptical Wing: • a. Tends to be even pressure over most of the surface. • b. Usually found in birds that live in forests. … facilitates a subtle change in the angle of the wing. • c. Sparrows. • High speed Wing: a. Falcons, Plovers • b. Wings that are narrow and come out to a sharp tip. These wings reduce drag. More of the wing-beat is producing forward thrust. • High lift Wing • a. Extreme slotting in the wing-tips • b. Vultures, Eagles, etc. How Hummingbirds Fly: The key to a hummingbird's flight is in its wing patterns. Generally, birds flap their wings up and down. This is not the case with the hummingbird, however. The hummingbird flies by oscillating its wings forward and backward in a figure eight pattern very rapidly. Seventy-five percent of the bird's lift is produced during the downstroke of this wing pattern. The figure eight pattern can be likened to a swimmer doing figure eights in the water to remain afloat. Bat flight vs. bird flight – which one is most efficient?! Unlike insects and birds, which have relatively rigid wings that can move in only a few directions, a bat’s wing contains more than two dozen joints that are overlaid by a thin elastic membrane that can stretch to catch air and generate lift in many different ways [video]. This gives bats an extraordinary amount of control over the three- dimensional shape their wings take during flight, Swartz explained. “Insects can move the joint at the insect equivalent of a shoulder, but that’s the only place where they can exert force and control movement,” she said. Birds have many more joints in their wings, but it’s nothing compared to bats. “Bats are operating with the same skeleton that we have. Every joint in the human hand is there in the bat’s wing and actually a couple more,” Swartz told LiveScience. “Think about the degree of control that we have over the shape of our hands—bats are able to extend that to make fine scale adjustments during flight.” It was once thought that despite having so many wing joints, it was more efficient for bats to stabilize their wings and wave them up and down like relatively rigid paddles the way birds do. “What we see when we look more closely is that in fact, it’s not what they’re doing,” Swartz said in a telephone interview. “It suggests that they’re able to take advantage of this highly jointed system to make subtle adjustments to the wing shape during flight.” The other key to a bat’s efficient flight lies in its highly elastic wing. Videos from the wind tunnel tests show that a bat’s wing is mostly extended for the down stroke during straightforward flight. But because the membrane can curve and stretch much more than a bird’s wing can, bats can generate greater lift for less energy. By blowing non-toxic smoke over the bats [video] as they were flying, the researchers were also able to create a video that revealed how air flows around the creatures as they flap their wings. The data showed that during the down stroke, the air vortex—which generates much of the lift in flapping-wing flight— closely tracks the animals’ wingtips. But in the upstroke, the vortex appears to come from another location entirely, perhaps the wrist joint. The researchers think this unusual pattern helps to make bat flight more efficient and credit it to the tremendous flexibility and articulation of the wing. Insect Flight Basics Insect wings are driven up and down by flight muscles located in the animal's thorax. There are two types of insect flight mechanisms, based on how the flight muscles transmit force to the wings. They are called direct and indirect flight mechanisms. In the direct flight mechanism, at least one power muscle connects to the wing…DIRECTLY! For example, a wing depressor muscle might attach to a special part of the wing near the wing base, and directly pulls the wing down when the muscle contracts. The direct flight mechanism is more primitive than the indirect mechanism, and so we find it on older insects (evolutionarily speaking), such as dragonflies and mayflies. Make no mistake, however – insects with the direct flight mechanism are not inherently worse flyers than those with the more advanced indirect mechanism. In fact, dragonflies are some of the most impressive fliers out there, due in part because their direct flight mechanism allows them to independently control each of their 4 wings.