Chordata-Aves


 * AVES (birds) **

Rachel Grasfield
 * There are approximately 2,800 different species, categorized into 28 different orders **

__**The Diagnostic Characteristics that Define Aves: **__ Evolution – Aves evolved during the **reptilian radiation**, which occurred sometime during the Mesozoic era. Lasting characteristics of reptiles can be seen in modern Aves in their amniotic eggs and scaled legs. The most famous of the Mesozoic birds are the **Archaeopteryx**, which first emerged during the late Jurassic period. The Archaeopteryx had forelimbs, teeth, a long tail, and feathers. Due to its wing structure, paleontologists determined that it was a "weak flyer"; they probably used their wings solely for gliding from tree to tree. Although the Archaeopteryx is not a direct ancestor of modern Aves, it does provide a link in avian evolution from reptiles to birds. Fossils found in China of **Confuciusornis** shows a closer to kinship with Aves; it is between the Archaeopteryx and modern Aves in terms of evolution. The Confuciusornis had no teeth or tail, and it had feathers. Below are two pictures of Aves ancestors; one is a fossil and another is a drawing depicting a guess as to what scientists believe the ancestors looked like.

__Anatomy__ – __Anatomy __ - Every characteristic of an Aves’ anatomy is modified to enhance flight. The bones of Aves are **honeycombed**, which means that they are not solid throughout, but have tiny fissures in the bone itself. This is advantageous because it makes the bones much lighter than other mammal bones; an important factor in aerodynamics. Aves also have **missing organs** and structures that aren’t used and therefore only serve as weight; for example, female Aves only have one ovary. Because flying requires a lot of energy, Aves are endothermic, which means that they use their own metabolic heat to maintain a warm, constant body temperature. **Feathers** are a feature of Aves that help insulate their endothermic bodies. Feathers are a very important diagnostic characteristic for defining Aves. Feathers are made of **keratin**, the same material found in human hair and nails. Feathers serve many purposes; attracting a possible mate, to forming airfoils, which work similarly to an airplane’s wings in terms of aerodynamics. Although feathers are essential in flying, it has been hypothesized that feathers did not evolve strictly for aerodynamic purposes, but rather as a form of thermoregulation. Aves have four different types of feathers. **Down** Feathers are soft and keep all birds (regardless of age) warm. **Filoplumes** are thin, hairlike feathers. **Contour** Feathers are the feathers that give Aves their color, and they provide protection. **Quill** Feathers are big and strong, and they assist Aves in flying by being components of the wings. (NI) [|4]. Another characteristic in relation to flight is that birds can be either **precocial** or **altricial**. Those that are precocial are born with feathers and learn yo fly on their own.Those that are altricial are born without feathers and attain a high parental investment. (KS) Below is a picture and diagram of honeycombed bones, mentioned above.

__**Acquiring and Digesting Food: **__ The diet of Aves ranges across a broad spectrum, from bugs to plants to fruits to seeds. Some birds such as raptors, owls, and vulture, eat meat from animals, such as small mammals and fish. They have **unique beaks and talons adapted** to catching and tearing meat. [[|6]][LJ} Aves acquire food by picking it up in their beaks. Therefore, the bird's beak must be adapted so that it can eat the food most efficiently. The beak of the bird changes depending on its diet. Darwin noticed this when he studied his finches; the bird's beaks were long and thin or short and thick depending on what their diet contained of. This is true for all birds, not only finches. A bird's **beak can tell a lot about its diet**. In the example below, one can interpret that in dry years, the vegetation changes, causing the bird's beak to evolve to fit this change. There is a clear pattern that in dry years, the medium ground finch's beak depth changed, indicating a change in diet.  [[image:23-13-DirectionalSelect-L.jpg width="466" height="360" align="center"]]

Most animals have **digestive tubes** that extend internally throughout the body, beginning with ingestion and ending with excretion. This tube is called the **complete digestive tract**, or the **alimentary canal**. An advantage of complete digestive tracts is the ability to ingest food before earlier foods have been completely digested in the body. Food moves along the complete digestive tract in one direction, which means that the tract is divided into specialized regions. In Aves, bird enters through the **mouth** and **pharynx**, passing through the **esophagus**. The food then passes through the **crop** and **stomach**, which serve as food storage organs, and then the **gizzard**. Modern Aves do not have teeth, due to the fact that they only add extra weight. Because of this, Aves do not chew their food; the food is ground down in the gizzard. The gizzard serves to digest the food. The gizzard is also known as the **ventriculus**. It is one of two main parts of the stomach, the other being the **proventriculus**. The proventriculus is the glandular portion of the stomach that secretes digestive juices which break down the food. (AK) (2) Once it passes through the gizzard, it enters the **intestine**, where the food is hydrolyzed by digestive enzymes and its nutrients are absorbed across the lining of the digestive tract and into the bloodstream. The undigested and unwanted food is eliminated through excretion.

__**Sensing the Environment: **__ Flight requires strength in certain sensory areas. Aves have an excellent sense of **sight**, far better than many other mammals, including humans. For example, a hawk can see three times better than humans. (KS) Studies have shown that the **visual and motor areas of the brain** are very well developed, as well as the fact that Aves’ brains are larger in proportion to other mammals. Birds also seem to possess sensory of their environment when they **migrate** annually. Scientists are unsure of the exact cues that animals use when migrating. Some species of Aves use a combination of **compass references**. They use the **Earth’s magnetic field**, **the sun** for daytime travel, and **the stars** for nighttime travel. When all three are used, a bird is able to travel globally in an expertly calculated route. Such utilization of surroundings shows how acutely Aves have adapted to their surroundings and sensing changes in their surroundings. <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; margin-bottom: 0in;"> //<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">The two pictures above show the migratory patterns of birds. It is an amazing phenomenon that birds can travel across the country each year unfailingly. They return to the same place annually. This is not only a characteristic of flying birds; penguins migrate each year as well, returning to the exact place where they migrated before. This characteristic clearly shows that Aves have developed a very strong sense of their environment. //

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">Some birds have another sense that can help them survive: **smell**. Pigeons may find their lofts from navigating based off of smells in air currents, Storm-Petrels are thought to find their burrows purely based on smell. Smell doesn't seem like popular sense for birds, who focus more on sight, but the necessary components for smelling are found in the nasal passages in all birds. The most popular use of smell is to **find prey**- Kiwi birds sniff to find earthworms, and some birds like the Northern Fulmar are attracted to smells of fish, krill, and squid. It is also known that turkey vultures have a very strong sense of smell, although the face if they use it to find prey is debated. (TM)(8)

__**<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; margin-bottom: 0in;">Locomotion: **__ <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; margin-bottom: 0in;">Aves generally use **flight** as a means of locomotion. Aves flap their wings by contraction of the **pectoral muscles**, which are attached to a **keel** on the **sternum**. Due to adaptations, some Aves can flap their wings rarely and utilize air currents and the wind to fly. These types of Aves include eagles and hawks. Other Aves, such as the hummingbird, must continually flap its wings in order to stay air-bound. Whether an Aves needs to flap its wings rapidly or hardly ever, the shape and arrangement of feathers of the Aves will always form the wing into an airfoil. There are, however, a group of birds that do not fly due to the fact that their sternum lacks the keel. These Aves are called **ratites**, which is Latin for “flat-bottomed” and they include the ostrich, the kiwi, and the emu. An unusual case would be the **penguins**, which have strong and attached pectoral muscles, but use them instead for swimming, rather than flying. //<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">This is a picture of airfoils, which were mentioned earlier on the page. Airfoils are the shapes of the wings of the birds. The airfoils of a certain species of Aves will be different because their flight patterns are different; airfoils evolve to help improve locomotion through flight. // media type="youtube" key="8ysATS8g-ac?fs=1" height="344" width="425" align="center"

(MLK)

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">Birds achieve flight much in the same way airplanes do. The birds’ wings are shaped so that there is a **pocket of high pressure** under the wing and lower pressure above the wing. This creates **lift**. One important factor in achieving lift is **speed**. When a bird doubles the speed, it gets 4 times the lift, and when it triples the speed, it gets 9 times the lift. (CC) ([|5])Birds also move through **walking** and **swimming**. Terrestrial birds, such as peasants, tend to move through walking. Arboreal birds, such as songbirds, tend to **hop**. Some birds such as hummingbirds tend to use their feet only for **perching**, and rarely walk. Most birds walk **parallel to the ground**. However, penguins waddle, with a combination of tobogganing, sliding and thrusting the feet. Some birds, such as ducks, use wings to not only fly, but to propel themselves in the water. Penguins, for example, have wings that are designed to **"fly" through the water**; webbed feet are designed to steer the bird. Auks, which differ from penguins, use both the wings and webbed feet to swim/move throughout the water. Loons spend almost all their time in the water; they have difficult moving on land. Pond ducks, including mallards and teals, swim at the surface, and feed by dipping their heads down into the water. Scoters and Pochards can dive to the bottom of a pond for food. (SI) (10)

__**<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; margin-bottom: 0in;">Metabolic Waste Removal: **__ <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; margin-bottom: 0in;">Like their ancestors, the reptiles, Aves excrete **uric acid** as their major form of nitrogenous waste. Uric acid is similar to urea in that it is **non-toxic**. However, uric acid is different to both ammonia and urea in that it is **mainly insoluble** in water, and it can be excreted as a semisolid. This is advantageous because it causes **little to no water loss** during excretion. Many marine Aves, like the albatross and the seagull, spend much of their time on open water, which means that they need to sustain themselves with drinking only salt water. They are able to do this by the evolution of nasal glands that can secrete excretions that has a higher salt composition than the ocean itself. Therefore, even though the bird is drinking salt water, it has a net gain of pure water. This is an adaptation of sea birds, and it is not a characteristic of all Aves.



__**<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">Respiration: **__ <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; margin-bottom: 0in;">Respiration in Aves is particularly **efficient** due to the fact that flying is an extremely costly process in terms of energy, and a bird needs to be able to receive as much oxygen as possible with as lost energy as possible. Because it has to be as efficient as possible, the result is a rather complicated process. Besides their singular lung, Aves have approximately eight or nine **air sacs**, which penetrate other parts of the body, such as the abdomen, neck, and wings. Air sacs are characterized as either **anterior** (at the front of the body) or **posterior** (at the back of the body). The air sacs are not directly functional during the actual process of respiration; instead, they keep air flowing through the lungs. The development of air sacs may improve aerodynamics because it **reduces density**. Both lungs and air sacs are ventilated when the bird inhales. During **inhalation**, the air sacs are full. Air then flows through the system in a circuit, passing through the lungs in only one direction. The direction does not change depending on whether the bird inhales or exhales. Aves do not have alveoli; they have tiny channels called **parabronchi**, through which air flows in one direction. When a bird **exhales**, the air sacs are empty, but the lungs are full from the air that was in the air sacs during inhalation. The system of respiration in Aves is advantageous because it completely exchanges air in the lungs in every single breath. This **maximizes oxygen concentrations** in the lungs, which is why Aves are able to function at higher altitudes.



__**<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; margin-bottom: 0in;">Circulation: **__ <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; margin-bottom: 0in;">Like respiration, circulation in birds is very efficient. They are characterized as having a **four chambered heart**. In all birds and mammals, the ventricle is divided completely into **two separate chambers**, a left and a right. In this division, the left side of the heart both receives and pumps exclusively oxygen-rich blood, while the right side of the heart handles oxygen-poor blood. The delivery of oxygen is increased because the oxygen-rich **blood does not mix** with the oxygen-poor blood. It is also beneficial because the double circulation restores pressure to the circuit after blood has passed through the lung capillaries.



<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; margin-bottom: 0in;">The main source of self-protection in Aves is their ability to **fly**; if they are being pursued by a land-bound predator it is very easy for them to escape. Aves also have different **colors**, which can be useful for camouflage and blending into its surroundings. Birds are very unique looking; their colors and patterns have derived from adaptations to their environments and colors that suits their niche. Because of their coloration, birds can also use their colors to their advantage. Birds are capable of **Mullerian** and **Bastilian** mimicry; when a species mimics a harmless or harmful species respectively. Using their wing patterns and colors, birds are able to use this advantage to ward off potential threats. They also use their **calls** to signal attacks or for self defense. The mocking bird, for example, will make several different bird calls that are not his own. Another form of self protection for birds, is **living alongside** other species of birds, that help protect from predators "Some birds actively cooperate with other species. By nesting close to animals better equipped to deter predators, the birds are inadvertently protected by their neighbors." Birds also like to **conceal their nests**, to protect the young and the adults "Many birds build isolated, inconspicuous nests, hidden away inside the vegetation to avoid detection by predators." (MP) [|7]]
 * <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; margin-bottom: 0in;">__Self Protection__: **

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; margin-bottom: 0in;">The energy cost of **osmotic balance is derived from the type of environment** the bird is living in, and how different in osmolarity that environment is from the bird itself. This means how easily water or solutes can move across its surface, and how much of a membrane transport it needs to move these solutes. Aves therefore adapt their osmotic balance to their environment. For example, desert Aves that eat mainly insects have evolved so that they lose very little water in their excretion. Bird excretion in general is characterized as a white paste, which is beneficial because it minimizes water loss.
 * <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; margin-bottom: 0in;">__Osmotic Balance__: **

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; margin-bottom: 0in;">Aves are **endothermic**, which means that they use their own heat gained from **metabolism** to maintain a constant, warm temperature. Feathers, while important in flight and aerodynamics, enable Aves to maintain their body temperatures. Feathers are excellent providers of **insulation**; they help retain metabolic heat. Fossils found of early reptilian Aves that did not fly but possessed feathers seem to suggest that feathers first evolved to help with temperature balance and insulation, rather than to help with locomotion and flight. "Generally, mating is accompanied by an elaborate courtship ritual. Eggs and often young birds are more **exothermic** (are not able to control their body temperatures from within) and so must be brooded/incubated by parents." [MS] [|3]
 * <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; margin-bottom: 0in;">__Temperature balance__: **

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; margin-bottom: 0in;">1. Describe the process of respiration in birds and how it allows birds to maximize their oxygen takeup. What are the advantages and disadvantages of air flowing in only one direction? (DB) <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; margin-bottom: 0in;">2. Why is having honeycombed bones in the birds wings an adaptation to fly? Explain what honeycombed bones are (SD). <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; margin-bottom: 0in;">3. Explain the advantages to having a four-chambered heart. How does the efficiency compare to that of a species with a two-chambered heart. How has this characteristic affected the abilities of birds? (CW) <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; margin-bottom: 0in;">4. Describe the waste removal of certain birds in relation to their osmotic balance. Why is it so beneficial for some? (GR)
 * <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; margin-bottom: 0in;">__Review Questions__: **

Sources:  1. Campbell, Neil A, and Jane B. Reece. . Sixth Edition. San Fransisco: Pearson Education, Inc, 2002. 2. [] 3. [] 4.[| http://www.mcwdn.org/Animals/Bird.html] 5. http://wings.avkids.com/Book/Animals/intermediate/birds-01.html 6.[] 7. http://www.pbs.org/lifeofbirds/home/index.html 8.[] 9.http://www.ucmp.berkeley.edu/diapsids/birds/birdlh.html 10. http://www.britannica.com/EBchecked/topic/66391/bird

Video: 1. http://www.youtube.com/watch?v=8ysATS8g-ac