It breaks down slowly in the soil and is very good at improving the physical condition of the soil whereas manure and sludge may break down fairly quickly, releasing a flush of nutrients for plant growth. The components of the digital TLM include a 'textured' pad on the ventral surface of each flexor tendon that contains thousands of minute, rigid, well-defined projections called tubercles see figure below. Researchers install a nest box in a field of blueberry bushes in Michigan. A tropical horde of counterfeit predator eyes. Ptolemeian rulers patronized ancient cults like the Apis, Mnevis and Buchis bulls.
The origin of feathers
The circulatory system of birds is advanced over that of reptiles in several ways: The avian lung differs from the type found in other land vertebrates in that several pairs of nonvascular air sacs are connected with the lungs. These extend into the pneumatic parts of the skeleton. Muscles between the sternum and trachea or along the trachea and bronchi vary tension on the membranes. The avian digestive system shows adaptations for a high metabolic rate and flight. Enlargements of the esophagus, collectively called the crop, permit the temporary storage of food prior to digestion.
The stomach is typically divided into a glandular proventriculus and a muscular gizzard , the latter lying near the centre of gravity of the bird and compensating for the lack of teeth and the generally weak jaw musculature. Otherwise, the digestive system does not vary markedly from the general vertebrate type. Like reptiles, birds possess a cloaca , a chamber that receives digestive and metabolic wastes and reproductive products.
A dorsal outpocketing of the cloaca, the bursa of Fabricius , controls antibody-mediated immunity in young birds. The bursa regresses with age, and thus its presence or absence may be used to determine age. The testes of the male bird are internal, like those of reptiles.
Intromittent organs are found in only a few groups waterfowl, curassows , tinamous , ratites. The distal part of the vas deferens the seminal sac becomes enlarged and convoluted in the breeding season and takes on both secretory and storage functions.
In songbirds this enlargement and the adjacent part of the cloaca form a cloacal protuberance, a swelling visible on the outside of the bird. Usually only the left ovary and oviduct are functional. As the egg moves down the oviduct, the albumen, membranes, and shell are laid down.
The gonads and accessory sexual organs of both sexes enlarge and regress seasonally. In the breeding season, the testes of finches may increase more than times their winter size.
This temperature may be slightly less during periods of sleep and slightly higher during intense activity. Feathers, including down, provide effective insulation. In addition, layers of subcutaneous fat add further insulation in penguins and some other water birds. Heat loss through the feet in cold weather is minimized by reducing blood flow to the feet and by a heat-exchange network in the blood vessels of the upper leg, so that the temperature of blood flowing into the unfeathered part of the leg is very low.
Birds do not possess sweat glands. Excess heat is dissipated by rapid panting , which reaches respirations per minute in domestic hens. Some heat can also be lost by regulation of blood flow to the feet. In hot climates, overheating is often prevented or reduced via behavioral means by concentrating activities in the cooler parts of the day and seeking shade during the hot periods. Temporary hypothermia lowered body temperature and torpor are known for several species of nightjars, swifts, and hummingbirds.
Torpor at night is believed to be widespread among hummingbirds. The heart rate of birds varies widely—from 60 to 70 beats per minute in the ostrich to more than 1, in some hummingbirds. The kidneys lie in depressions that are located on the underside of the pelvis.
The malpighian bodies , which are the active tubules of the kidney , are very small in comparison with those of mammals, ranging from 90 to per cubic mm. More than 60 percent of the waste nitrogen is excreted as uric acid or its salts. There is some reabsorption of water from the urine in the cloaca, with uric acid remaining. There is no urinary bladder , the urine being voided with the feces. In marine birds, salt is excreted in a solution from glands lying above the eyes through ducts leading to the nasal cavity.
The origin of birds, feathers, and avian flight have long been hotly debated. That birds evolved from reptilian ancestors is universally accepted, but did they evolve from thecodont reptiles or theropod dinosaurs? How and when did feathers evolve from the scaly reptilian integument? Did avian flight evolve from a terrestrial ancestor or an arboreal one?
Such debates continue to be fueled by regular discoveries in China and Mongolia of remarkably preserved fossils from a critical period in avian evolution—the Early Cretaceous The diversity of theropod dinosaurs, some with feathers, has greatly expanded our perspective of the evolution and early diversification of birds.
Two major groups of early birds diversified dramatically in the Cretaceous Period: Paleontologists now position Archaeopteryx , once thought to be a direct ancestor of birds, and several other fossil taxa at the base of the extinct enantiornithine lineage.
The debate over the origin of birds centres on whether birds descended directly from thecodont reptiles about million years ago during the Triassic Period or from a later lineage, the carnivorous theropod dinosaurs. This debate has been long-standing and divisive. This hypothesis is supported by analyses of shared characteristics synapomorphies combined with improved samples of early bipedal theropods. Feathers are complex and novel evolutionary structures. They did not evolve directly from reptilian scales, as once was thought.
Current hypotheses propose that they evolved through an invagination of the epidermis around the base of a dermal papilla, followed by increasing complexity of form and function.
They evolved before birds and even before avian flight. Thus, early feathers functioned in thermal insulation, communication, or water repellency, but not in aerodynamics and flight. Among extinct life-forms, feathers are no longer considered a unique and diagnostic characteristic of birds. Feathers with modern features were present in a variety of forms on a variety of theropod dinosaurs.
At least nine Cretaceous dinosaurs had featherlike structures. The details of some are questionable, but some, such as those of Sinornithosaurus and other basal dromaeosaurs, bear a resemblance to modern pennaceous feathers.
Feathered dinosaurs did not survive the end of the Cretaceous Period , but birds did, and then they flourished. Experts continue to debate whether flight evolved through gliding by an arboreal ancestral bird or through aerial launching by a running terrestrial ancestor.
Historically these two hypotheses have been strongly linked to, respectively, the thecodont origin hypothesis and theropod origin hypothesis. The shift of opinion toward the theropod hypothesis, however, does not resolve this debate, since feathers on the forelimbs of early birds could have facilitated the early stages of flight through either mode.
Precursors of an effective flight stroke of the forelimbs were present in terrestrial bipedal theropods. In either case, the evolution of avian flight required a decoupling of coordinated movements of the forelimbs and hind limbs.
It also depended on new neural links between forelimb and tail movements as well as on other elaborations essential to controlled flight without major initial compromises of terrestrial locomotion. Once controlled flight had evolved, the avian body plan was transformed into a powerful flight engine.
The transformation was then followed by the loss of other capabilities—or, in some cases, of flight itself. A series of fossils, each dated to approximately million years ago during the Jurassic Period , were about the size of a magpie. One of smooth muscular fibres, longitudinally arranged. The tunica submucosa of loose connective tissue, which contains nerves, blood, and lymphatic vessels.
The tunica mucosa or innermost lining, composed of epithelial cells, which give rise to mucous and various specific digestive glands. It is noteworthy that Birds and Reptiles differ from Mammals in the succession of the two muscular layers 2 and 3 , since in the last the circular fibres are placed on the inside, next to the submucosa 4 , while the longitudinal fibres together with the serosa 1 form the outer wall.
These layers vary considerably in the different parts of the Alimentary Canal; thus the thickening of the walls of the gizzard is due to the excessive development of the muscular, layers, while in the oesophagus the mucosa is represented chiefly by ordinary epithelial cells, comparatively few of which form simple mucous glands, though in the region of the proventriculus its cells are transformed into large glands, often closely packed and compressed, constituting the greater part of the thickened walls.
Again, in the gizzard no such specific, but only mucous glands occur, the hardened secretion of which invests its cavity with an additional cuticular lining. This is the reason that some people recommend feeding baby birds from the left side of the beak, with the syringe pointing to the right, although, in reality, it shouldn't matter which side of the beak a baby bird is fed from.
The trachea windpipe also curves to the right in the neck. Also found in the neck are the paired jugular veins, with the right jugular usually being much larger. Avian vets may use the right jugular vein to draw a blood sample. Generally, the neck is carried in a double curve, which forms an "S". Since the forelimb has been completely committed to flight in birds as a group, although some birds, such as the emu and ostrich cannot fly , the bill has assumed the ability to perform many functions normally carried out by the mammalian forelimb, such as grooming and nest building.
Anyone that owns a parrot knows that the beak is used, along with the tongue, to explore its environment. A person unfamiliar with birds may pull away when a bird that has had a hand extended to it to be picked up, reaches beak-first towards the hand prior to stepping aboard. The novice may incorrectly assume that the bird is going to bite him, but the bird is just using the beak to test the waters, so to speak, prior to stepping up.
Since the neck forms an "S" curve, it protrudes forward in the front, above the level of the crop. Often, this may be mistaken for a tumor or abnormality in the neck, especially when the crop is empty and the bird is sitting comfortably. Because the neck has more vertebrae than a human's and mammal's, the avian neck is extremely flexible, mobile and strong.
We've all seen how easily a owl can turn its head so much farther around than we can. The neck is considered one of the strongest parts of a bird's body, and it is almost impossible to injure a bird by holding it by the neck as long as the windpipe is not closed off , let alone break its neck, when it is properly restrained. Often, people think, when they pick up a limp, dead bird, that it must have broken its neck, because the neck is so limber.
It rarely is the cause of death. Birds that fly into a window or other solid structure may die, often of a concussion or other trauma, but in all my years of practice, I have only seen two birds with fractures of the cervical vertebrae.
In the front part of the neck of parrots, the crop or ingluvies is found. It is actually an outpouching of the esophagus, the tube that carries food from the mouth to the stomach. Many people think that all birds have a crop, but some do not, including the gull and penguin.
In the parrot, it is oriented transversely across the neck. In pigeons and doves, the lining of the crop is shed when they are feeding babies, for the first few days. This is called crop milk, and it resembles mammalian milk in that it is rich in fat and protein, however, it lacks carbohydrates and calcium, and contains no milk sugar lactose. The crop, in baby parrots, is very large, and shrinks down as the bird weans.
The trunk is the whole body of the bird between the neck and the tail. It is divided into the thorax , abdomen and pelvis. The thorax is bounded by the rib cage, sternum keel and vertebral column backbones. The abdomen and pelvis aren't separated by any well-defined boundaries. The top part of the trunk is divided into the back and rump.
The region between the right and left shoulder blades scapulae is called the interscapular region , and often carries distinctive streaks or colors.
The whole back, combined with the top surface of the wings, is called the mantle. Often these anatomical descriptions are used by judges during bird shows. The side area of the trunk is called the flank. The underside is divided into the breast , belly and undertail. Another area, the crissum , refers to the general area around the vent, along with the undertail covert feathers. The term, vent , should only be used to describe the actual orifice, and not the general area under the tail.
The tail contains the flight feathers called retrices which is Latin for rudders. The retrices are always paired, with the central one lying on the midline. The majority of birds have six pairs of retrices, but the number ranges from 6 to Tail coverts are small feathers that lie over and under the retrices. Interestingly, the coverts are greatly enlarged in the peacock, and form the eyed feathers of the train.
The pygostyle is the end-most bone of the spinal column. You may be more familiar with the term "the Pope's nose" for this extraneous piece found on a chicken thigh. If this bone has been fractured or injured, a male bird may not be able to successfully copulate with the hen. Moving on to the wing, we find that it is unique, as it is adapted for flight.
Many of the bones have become fused, and the skeleton of the hand manus has undergone considerable simplification. In addition to the bones of the wrist being consolidated, there are only three "fingers. These "fingers" have reduced phalanges our fingers have three phalanges each, except the thumb, which has two. Most commonly, the alula has one phalanx, the major digit has two, and the minor digit has one.
The propatagium is that elastic triangular fold of skin on the leading edge of the wing. This is the area where a tattoo is placed when a bird is surgically sexed. The feathers on the wing are divided into flight feathers remiges , further divided into primary and secondary flights and coverts. The primaries are the last ten wing feathers on the wing, and are numbered from ten to one, outermost to innermost.
The secondaries begin at the first bend of the wing, and are numbered one to twelve, from the bend inward. When wings are clipped, it should never be necessary to cut any feathers other than primaries, no matter which method is used.
The bones of the leg have also been modified. The thigh bone femur is the same as is found in mammals. The knee joint follows at the joint below the femur.
The next bone is different from that found in mammals. Several bones have fused to form the tibiotarsus bone. Basically, the ankle bones fused with the bones of the arch of the foot to form one long bone.
There is still a small fibula bone present. The next joint is called the intertarsal joint , and humans don't have one. The bone below that joint is called the tarsometatarsus , which also consists of fused bones. Think of the flamingo leg and how when you watch one walk, it seems as if the "knee" is bending the "wrong" way. That's because the elongated tarsometatarsus looks like the shin bone, so you think that the joint if it was the knee should bend in the other direction.
But actually the knee is up in the feathered area of the leg, which DOES bend the same way ours does. In most birds, the first toe is usually directed backwards, and the other three point forward, and this is technically known as the anisodactyl foot. This type of foot is called the zygodactyl foot. Swifts have a foot adapted for climbing, and all four toes point forward, and this is called the pamprodactyl foot.
Emus, rheas, many wading birds and some woodpeckers only have three functional toes, and in most of these birds, it is the first digit the hallux , which is similar to the big toe of man that is lost. The ostrich has only two toes, with digits I and II being lost. Some of the bones of the avian skeleton are hollow and connected to the air sacs of the respiratory system.
Most of the vertebrae, pelvis, sternum and rib bones are hollow and the marrow has been eliminated. The limbs vary in the degree of pneumaticity , and there are pneumatic spaces within the bones of the head, as well. This is important to reduce the weight of a bird to allow it to be light enough for flight. The skin of birds is different from other animals in several ways.
For one, only birds have feathers. Some birds have ornamental outgrowths, characterized by thickened skin that has many blood vessels. For example, some birds have a comb , a bright red vertical projection from the forehead and crown. Some birds also have wattles , which are naked folds of skin that hang down from the mandibles. Some birds have ear lobes , which are folds of skin, that may be red, white or purple.
The snood , also called the frontal process, and is a distensible fleshy process arising on the head between the eyes and nostrils of the turkey. Turkeys also have caruncles , which are small protuberances of skin on the head and upper neck. The skin of birds contains no sweat glands, so birds rely on evaporative cooling from the respiratory tract. The main gland of birds is the uropygeal gland , and is present in most birds and may be relatively large in some aquatic species.
It is absent in the emu, ostrich, many pigeons, Amazon parrots, and the hyacinth macaw, for example. Another adaptation with avian skin is the brood patch , an area over the breast that becomes thickened, very vascular and the feathers are lost during the brooding period. These modifications promote the transfer of heat from the hen to her eggs.
There are seven types of feathers, the contour , semiplume , down , powder down , hypopenna , filoplume and bristle feathers. The contours cover the surface of the body, and arise from feather follicles.
The follicle consists of a living part and a nonliving part. Growing feathers, or blood feathers , have an active blood supply until the feather is grown out completely. If a bird plucks out a feather from a follicle repeatedly, it my eventually destroy the living portion of the follicle, resulting in a follicle that can no longer grow a feather.
Feathers molt out when a new feather is developing in the follicle and the old feather is then pushed out. Normally, a plucked feather will begin to regrow from the follicle immediately, but a cut feather will not be lost until it is molted out. Most birds replace all their feathers yearly, and this is a continuous process, however, some birds molt during a particular time frame for example, after breeding season, or in the summer.
The skin of birds has distinct, well-defined tracts called pterylae that contain the feather follicles for contours. The bare spaces between the pterylae are called apteria. The digestive system has some unique avian features. We have already talked about the crop, the outpouching of the esophagus.
The esophagus connects to the crop and then travels through the bones at the top of the keel. The esophagus then connects to the stomach. The avian stomach is unique.
The first portion of it is called the proventriculus , and this is the part with glands in it that secretes gastric juice. The second part of the stomach is called the ventriculus , or gizzard, and it is where digested proteins are broken down and where grinding occurs.
When a bird has PDD, proventricular dilation disease, the nerves to the gastrointestinal tract are usually affected, and the proventriculus will become dilated, thin-walled, and impacted with food items. The ventriculus may also become more mushy and less muscular.
Some birds have paired ceca our appendix is really called the cecum , which is the singular of ceca. The big difference occurs when we examine the tail end of the digestive tract. Most people know that birds only have ONE external opening, called the vent , and the internal chamber, or cloaca, that is used for urination, defecation and reproduction.
Inside the cloaca , there are three separate compartments, called the coprodeum , the deepest compartment, and is the terminal end of the rectum.
The next cloacal compartment is the urodeum , and this is the middle section that collects urine and urates from the ureters , that drain the kidneys. In the hen, the left oviduct opens into the urodeum. When an egg is travelling through the reproductive tract of the hen, it enters the urodeum before it passes out through the vent.
The last compartment, just inside the vent, is the proctodeum. This compartment contains the avian phallus , if one is present. The phallus differs from the mammalian penis in several ways, the major ones being that it is just a copulatory organ and that is does not function to drain urine.
Male ratites ostrich, emu, rhea , ducks, geese, swans and some domestic fowl and turkey possess a phallus. Male parrots do not. The proctodeum is also the site of the Bursa of Fabricius , an organ that produces cells to fight infections. The bursa is unique to birds and should always be harvested for histopathology if a baby bird dies, because it is often very helpful in diagnosing many avian conditions and diseases.
The bursa begins regressing, called involution , several months after hatching, and will usually be completely involuted by sexual maturity, in most birds.
The urinary system of birds is different from mammals, as birds produce both urine and urates. The kidneys possess two different types of nephrons , the units that filter the blood to remove toxins and products of metabolism.
Birds cannot concentrate their urine as well as mammals can. Birds also are uricotelic , meaning that they excrete the end product of nitrogen metabolism as uric acid , which is made in the liver and they excreted from the blood.
Uric acid is the creamy white portion of the dropping. Urine is the clear portion.