birds

common characteristics :

class aves

most divers of all land vertebrates, range in size

found in deserts, forests, mountains, praises , on seas

have common ancestor with reptiles, have many reptile like features like amniotic eggs and scales covering their legs

endotherms

make their body heat by metabolism

high metabolic rate generates energy for flying and other purposes

high body temperatures enables cells in flight muscles to use energy for quick muscle contractions during flight

feathers : specialized outgrowths on birds skin

made of protein keratin

functions are flight and insulation. when a bird fluffs its feathers , it creates a dead air space that traps body heat

preening

barbs branch off from the shaft of these feathers and held together by hooks, if they are separated they can be rejoined like zippers

birds repair separations by preening ; runs the length of feathers through its beak. a preen gland near the base of the tail secretes oil over feathers to waterproof them

contour feathers cover the body , wings and tail

down feathers are soft feathers beneath contour feathers. they dont have hooks to hold barbs. this down structure allows down feathers to trap air for insulation

bones

large breast muscles provide flight power. the muscles connect the wing to the keel of sternum or breastbone

birds bones contain cavities of air, making skeletons lightweight

fusion creates skeletons sturdy enough for flight

systems

respiratory :

flight muscles use a lot of oxygen

a bird has more space for air than a reptile as well as one way circulation

only oxygen rich air moves through lungs and flows in one direction

circulatory

blood enters the left atrium from the lungs then pumped to the left ventricle to the body

blood then returns from the body to the right atrium and then to the right ventricle and to the lungs to pick up more oxygen

4 chambered hearts , two ventricles separate oxygen rich from oxygen poor blood

digestive

food travels through the esophagus to a storage chamber called the crop, then to the stomach

at the base of the stomach there's the gizzard, a thick muscular sac which has small stones in it and crushes the food along with the gizzards muscular action

digestion and absorption of nutrients occur mostly in the small intestine with help of digestive juices from the pancreas and liver

excretory

birds lack urinary bladder ( an organ for storing urine )

stored urin would add weight making it harder to fly

kidneys filter wastes from the blood and convert it to uric acid , water from uric acid is reabsorbed in the cloaca

not having a urinary bladder is a flight adaptation

bird adaptations

large brain

cerebellum coordinates movement and flight balance

optic lobes for visual input , the core of the large cerebrum controls most behaviours. the medulla oblongata controls automatic functions such as respiration

eye position reflects life habitats

hawks need to focus both eyes on prey, so their eyes eyes are located in the front of its head

pigeons need to see predators coming from any direction, so their eyes are on the sides on their heads

internal fertilization , the eggs are released through the cloaca or both parents sit on eggs to incubate them

orders

ecology and evolution

evolution :

ecology

fossils show that birds , crocodiles , and dinosaurs descended from archosaurs

fossils of 3 species of feathered birdlike dinosaurs were discovered in china

predators and prey in they food chains

important role in spreading seeds

hummingbirds pollinate flowers as they feed on nectar

bird habitats are disappearing as wetlands are drained for development , as well as pesticides and chemical pollutants destroying habitats , illegal capture also leads to disappearance of many rare birds

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