How Seagulls Fly
This site contains information and facts about how seagulls, and birds in general, fly. While the information and facts on how seagulls fly that I have posted is not all-inclusive, I have done my best to list as much pertinent information and facts that I could find. My hope is that my site will make your reseach on seagulls much easier.
The first and most obvious thing that you will notice about a bird is its feathers. They are very light while at the same time very strong. They are very flexible while at the same time very tough. Oddly enough, feathers do not grow all over the bird. The entire body of the bird may appear to be covered with feathers, but this is not the case. A bird's feathers only grow in certain areas on its body called feather tracks. In between the feather tracks are tiny “down” feathers. These “down” feathers actually help to minimize the weight of the bird's body. The “down” feathers are extremely small and soft, providing a layer of insulation that protects the bird from extreme temperatures.
Feathers are made of a tough and flexible material called “keratin” which just happens to be what the bird's beak is made of. While feathers may look solid, they are actually not solid at all. The spine down the middle, called the Rachis(2), is hollow, and the pointed end, called the Calamus(5), or quill, is also hollow, which makes the feather very light weight. A small opening, called the “superior umbilicus” is located at the junction of the rachis and calamus. A small feather known as an after feather(4) is often attached to this small opening. There are vanes(1) are on the two halves of the Rachis. These vanes are made of thousands of branches called barbs(3). It is interesting to note that there are many spaces, or air gaps, between these barbs which means that a feather has as much air as matter.
A bird's survival depends upon the condition of its feathers. Because of this, birds take a lot of time caring for their feathers. This is called preening. They use their feet and beaks to carefully arrange and clean their feathers. When cleaning, they nibble each feather from the base of the tip. Birds also bathe a lot to keep their feathers in top notch condition. Seagull's have a preen gland, or “uropygial” gland, at the base of the tail. This gland produces uropygial oil which is a waxy substance that is used to waterproof and condition feathers. By rubbing the preen gland with its beak, the seagull picks up the oil and then distributes it onto its feathers by rubbing its beak over the feathers, It is possible that the oil from the preen gland also helps to make the feathers supple and strong and prevents them from drying out .
Birds have between 1,000 and 25,000 feathers, depending upon the size of the bird. A humming bird has fewer feathers than a swan. A bird's feathers can be divided into 6 categories:
- Contour feathers (cover the body of an adult seagull and determine its shape).
- Semiplume feathers (supply thermal insulation and a certain amount of shape).
- Filoplume feathers (keeps the other feathers in proper order and shape, and also provide sensory information about the position of adjacent contour feathers).
- Bristle feathers (provides protection around the eyes and mouths of some birds and have a sensory function).
- Down feathers (provide thermal insulation).
- Powder-down feathers (forms a waterproof barrier for contour feathers).
Not all birds have all of these types of feathers. It all depends on what type of bird it is. One that all birds have in common is the feathers on their wings. The bird's wing is obviously the basic structure for flight. It is the very shape of the wing that allows a bird to fly. The shape of the wing is made by the feathers. The flight feathers are called remiges and have a leading edge that is much smaller than the trailing edge. This is because the air pressure on the leading edge of the feather (the part that faces forward) are much greater than those on the trailing edge. This provides the “lift” that allows the bird to fly and soar.
The tail feathers, called retrices, of the bird also play a large role during flight. The tail acts as the rudder that both balances and steers the bird. The tail also helps the bird in coming to a stop. The tail is turned downward which causes it to act like a brake.
The Mechanics of Seagulls in flight
The natural shape of a wing is called an airfoil. As the wing (airfoil) moves through the air, air flows above and below. The air flow over the upper surface has to move farther than the air flow under the lower part of the wing. Due to this air flow, the air on the upper part of the wing has a lower pressure than the air moving under the lower part of the wing. This difference of air pressure causes lift. The lift force occurs because the air has a lower pressure just above the wing and higher pressure below the wing. In other words, a seagull with air moving over its wings is pulled up from above and pushed up from below.
When a seagull flaps its wings (as opposed to gliding) its wings continue to develop lift as before, but they also create an additional forward and upward force, called thrust, to counteract its weight and drag. Wing flapping involves two stages: the down-stroke, which provides the majority of the thrust, and the up-stroke, which can also provide some upward force. On each up-stroke the wing is slightly folded inwards to reduce upward resistance. This allows the seagull to change the angle of attack between the up-stroke and the down-stroke of their wings. During the down-stroke the angle of attack is increased. During the up-stroke the angle of attack is decreased. This action causes the wings to act like the propeller on an airplane to pull the seagull forward.
Speed is the most important part in making lift. Speed can be increased by increasing the forward speed of the wing itself as it travels through the air. The seagull makes its forward motion and speed by flapping its wings. We previously defined this forward motion as thrust. If a seagull doubles its speed, the bird gets four times the lift. If the seagull triples the speed it will get nine times the lift.
Sometimes seagulls can glide and soar for a long time. It seems like they almost “drift” along a beach while they look for their next snack. How do they do this? If the power does not come from flapping their wings, where does it come from?
The seagulls are taking advantage of upward movements of air called thermals. The seagulls are resting on currents of air that are moving upward. Many seagulls find these thermals and use them for the upward push they give. These seagulls are slowly gliding downward on a constantly rising current of air.
Unfortunately for the gulls, warm air does not rise from the ground in an even manner. This air is shaped more like a circular column, although not perfectly round. Riding thermals are great energy savers for the gulls when they can find them. The Sun warms the ground, which in turn warms the air directly above it. It is not uncommon for seagulls to wait on the beach until around 10 o'clock in the morning for the thermals to form. They will then use these thermals to glide along the beach searching for a mid-morning snack.
There are other kinds of updrafts also that the seagulls take advantage of. Obstruction currents are made when moving air runs into an object like a cliff, mountain, or sand dune. The air is forced up and over the object. Seagulls can “ride” these currents high up into the air.
Take Off and Landing
The time in any flight that presents the greatest hazards to seagulls is during take off and landing. At take off, it is because speed is related to the lift needed to leave for the seagull to rise up into the air. Lift for the seagull is the weakest at take off because full speed has not yet been made. When a seagull starts to land, lift becomes weakened because the speed of the bird is being reduced.
The size (length) of the wing is what determines how much lift is made. The angle at which the seagull's wing approaches the air (angle of attack) also affects lift. This increases the air speed over the seagull's wing and produces more lift. Seagulls change their wing size (by stretching their wing out as much as possible), lower the rear portion of their wings, use winds, and increase their speed by flapping their wings faster. Watch a seagull take off sometime and you will observe them using all these techniques simultaneously.
Landing is harder for a seagull than the takeoff. The gull must end his flight slowly and carefully. First, the gull slows its wing beats to slow its speed. Next, gravity takes over and begins to pull the gull downward. The gull will next twist its wing to increase the surface area of the wing. The purpose of this is to produce more lift to slow the gull's downward descent. At the same time, the whole wing is moved slightly at the shoulders to increase the angle of landing. This provides maximum lift as the gulls speed is slowed. This prevents the gull from dropping too fast. Lastly, the tail is spread open and lowered to act as a brake. While all of this sounds very complicated, seagulls make it look easy.
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