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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