The main concern of all animals is finding enough food to survive. It is advantageous for a species to have an alternate food supply than most other animals. Hummingbirds(order Trochilioformes, family Trochilidae) have an alternate food source. These birds get most of their food from the base of blossoms. They have a long tongue to lap up nectar and small arthropods at the bottom of these blossoms (Swifts and Hummingbirds 1985). To get this food the bird often has to hover over the flower. Hummingbirds are truly extraordinary because they are the only birds capable of performing true hovering ("Swifts and Hummingbirds", 1985). The hovering of hummingbirds is of particular interest to helicopter designers and ornitholgists. I personally find this topic interesting because I have a special interest in animals and biology. In this term paper I will discuss the problem of hovering in relation to the anatomy of the hummingbird. Hummingbirds are exceptional flyers. They can fly in any direction and can hover. When hovering the wings paddle horizontally, cycling back and forth in a figure eight motion (Long, 1997). While doing this the wings pivot so that the feathers push down air in either direction. To fly straight the hummingbird paddles its wings vertically instead of horizontally. Hummingbirds are also capable of flying in any direction. They can hover at a flower, lap up some nectar and then fly in reverse and take off. Having extraordinary fling ability also allows the hummingbirds to escape from predators and hunt for flying insects. Hummingbirds have been calculated to fly as fast as 60 mph while diving and 30 mph during straight flight ("Hummingbirds", 1997). They also have been calculated to beat their wings up to 200 times per second during diving ("Hummingbirds", 1997). Feathers are one of the major adaptations that allow birds to fly. The exposed body feathers of adult birds, in general, consist of a central shaft and an outer and inner vane made up of barbs and interlocking barbules and barbicels (Long ,1997). Hooklets, which are called hamuli, are microscopic (Long, 1997). They hold the parts of the vane together in a continuous, unbroken sheet (Long, 1997). If something disturbs this continuous unbroken sheet, the bird can fix it through preening. Preening is when the interlocking barbs and barbules are reunited by the birds beak. Feathers are made out of keratin and are produced by papillae in the skin (Lanyon, 1963). Feathers develop when strong vascular dermal tissue that is covered with a thin layer of epidermis forms a cone shaped structure (VanTyme, 1971). The epidermal layer sinks inward and forms a follicle out of which a papilla continues to grow and develops into a feather (VanTyme, 1971). The body plumage of the hummingbird is moderately dense and the feathers are firm and adherent to each other ("Swifts and Hummingbirds", 1985) Mature hummingbirds also do not have down. This is advantageous to the hummingbirds because it reduces weight. Their wings have ten primary feathers. These feathers are attached to the hand part of the wing and the outermost of these is always the longest. In other birds these feathers are longest toward the innermost part of the wing. Hummingbirds are one of the only species to have about six or seven secondary feathers on its wings (Long, 1997). These secondary feathers allow them to make exceptionally fast movements. When feathers from a wing are broken or lost, they are quickly replaced so as not to interfere with the ability of the bird to fly ("Hummingbird Family", 1998). Having light, strong bones is another adaptation that allow birds to fly. A bird’s bones are honeycombed. This make the bones light for flight yet still strong enough to support the pull of the muscles connected to them and the weight of the bird (Campbell, 1996). Bones are also a site for calcium storage and the production of red blood cells ("Anatomy and Physiology", 1998). The red blood cells carry oxygen that is need to sustain flight. Hummingbirds have a different bone structure that other birds. In their wing they have a short upper arm bone(humerus), short forearm bones(radius and ulna), and long hand bones(manus). This hand bone is as long as the upper and lower arm bones put together. Other bird’s wings have long upper and lower arm bones and a short hand bone. The hummingbird’s humerus is strong and is modified in configuration. The proximal articular surface is very small and is displaced to the inner side of the articular head of the humerus (VanTyme, 1971). This allows the humerus to rotate smoothly. The hummingbird also has a well constructed sternum. The sternum has to be strong because it is the site of the powerful flight muscles. These muscles are connected to the keen. The keen is a longitudinal plate of bone located on the under side of the sternum. The hummingbird’s shins and feet are short and the leg and foot bones are thin ("Swifts and Hummingbirds", 1985). This is because the hummingbird does not need to walk anywhere. The hummingbird prefers to fly over walking. It’s feet have three toes pointing forward and one toe reversed. It’s feet also has very sharp talons. It’s feet are very efficient at perching but are not suited for walking. Having thin, short leg bones helps save weight for flight. The powerful flight of the hummingbird comes from its pectoral and supracoriodus muscles. The pectoral muscles lower the wings. The hummingbird has the largest pectoral muscle relative to its body size in the animal kingdom (Dial 1990). The supracoriodus muscle is responsible for the raising of the wing. It is sometimes called the elevator muscle. The hummingbirds supracoriodus weighs from a third to a half as much as the pectoralis ("The Birds", 1988). In other birds it only weighs a tenth to a twentieth ("The Birds", 1988). This is because the hummingbird has to raise it’s wing with almost as much force as it lowers it in order to hover. The tendon of the supracoracoideus muscle is connected to the head of the humerus in a way that allows the humerus to rotate (VanTyne, 1971). In other birds the tendon of the supracoracoideus is connected in a way to elevate the humerus (VanTyne, 1971). The hummingbird also lacks muscles that are important in other birds. It’s wing are said not to have a biceps brachii muscle or a deltoideus major muscle (VanTyne, 1971). The deltoideus major muscle is important in wing elevation and the biceps brachii muscle is the main flexor of the forearm (VanTyne, 1971). The hummingbird has no need for muscles that bend the arm because it keeps the wing straight at all times. The absence of the biceps is compensated by the very high origin M. extensor metacarpi radialis and by the hypertrophy and peculiar insertion of M. tensor patagii brevis (VanTyne, 1971). The heart is also very different than other birds. It makes up a larger body mass than any other bird and is estimated to beat, at times, about 1200 times a second (Poet, 1998). The hummingbirds heart also has a right ventrical that is much larger than it’s left ventrical (Poet, 1998). These variations are designed to move a larger supply of blood. The hummingbird burns a huge amount of calories per day. The number of calories a hummingbird burns in a day would equal 155,000 for a human (McCausland, 1992). The hummingbird has to move a large supply of blood because it has a high metabolic rate and needs to supply its large flight muscles with oxygen. Birds, in general, have small capillaries which allows for a greater surface area for gaseous exchange ("What is a Bird", 1985). Birds have a large number of air sacs throughout their body spaces. These air sacs are thin-walled pouches that lack capillaries in their walls ("What is a Bird", 1985). When a bird breaths, air passes first through the posterior sacs and then into the lungs. From the lungs the air travels out of the bird through anterior air sacks. The blood vessels are efficient in their uptake of oxygen and disposal of carbon dioxide because of the direction of airflow. Blood vessels are arranged so that blood flows in the opposite direction of air ("What is a Bird", 1985). As oxygen depleted blood flows along against the lung wall it takes up progressively more oxygen and as air travels through the lung it gives up progressively more oxygen ("What is a Bird", 19985). The same thing happens, in reverse, for the disposal of carbon dioxide. Birds require more oxygen than most other animals to sustain flight. This forced the birds to evolve this more efficient respiratory system. The hummingbirds require even more oxygen than most other birds and had to evolve an even more efficient respiratory system. The hummingbird requires sixty-eight cubic centimeters of oxygen per gram of body weight per hour ("Swifts and Hummingbirds" 1985). Due to this need for oxygen during flight, the hummingbird’s breathing surface of it’s lung and size of it’s heart, in proportion to one gram of body weight, are three times as large as three times as large as pigeons ("Swifts and Hummingbirds" 1985). The bronchi of the hummingbird are also large to allow for more air to enter into the lungs. For a hummingbird to survive it has to get a large supply of food. The only way to get this food is to hover over a blossom and lap out it’s nectar. To do this the hummingbird had to overcome the problems of hovering. It did this over centuries through evolution. Without the different wing structure, bone structure, and muscle structure the hummingbird would not be able to fly. The hummingbird would also not be able to find food or survive. There will be more research in the future about the anatomy hummingbirds. There should be more research performed on the hummingbird’s heart. Not much is known about the effectiveness a heart has with a right ventrical that is considerably larger than its left ventrical. There should be more research done to discover if it is possible for hovering to be accomplished by birds or other organisms of larger sizes. It is also advantageous for the to study of the flight of hummingbirds to continue so that the mechanics of helicopters can continue to improve. The problems of hovering flight are astounding and should continue to be studied.
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