Section 12.5 Birds. Bird Evolution It appears birds have descend from bipedal crocodile like reptiles that existed 160 million years ago The oldest known.

Section 12.5Birds

Bird Evolution• It appears birds have

descend from bipedal crocodile like reptiles that existed 160 million years ago

• The oldest known bird is Archaeopteryx and its fossil shows traits similar to reptiles and birds– It may represent the

transition between the two groups

Archaeopteryx

• Diagrams show the fossil and artistic rendition

• Reptilian characteristics– Thick bones– Teeth– Long bony tail

• Bird characteristics– Elongated, wing like

hand– Feathers

Toothed beak

Airfoil wing with contour feathers

Long tail with many vertebrae

Wing claw

Class Aves

• There are around 9000 living species and subspecies today

• Birds are found in all habitats

• See wide range in birds:– Plumage– Behaviours (especially in

regards to reproduction)– Sound/song

Identifying and Classifying

• Birds are identified and classified largely based on structural features

• The two most familiar structures are:– Beak– Feet

• Using these 2 features alone divide birds into 5 common groups

Common Features Amongst Birds

• They have feathers– This is unique to birds

• Lay amniotic eggs with calcified shell• Have scales – Found on their feet

• Much of their anatomy is modified to enhance flight– Obviously we all know not all birds fly as there are many

flightless birds, but by far more birds fly than do not

Characteristic for Flight• Some of the key features

for birds flight to be possible are:– Feathers– Wings– Light skeleton and breast

bone– Large pectoral muscles– Efficient circulation and

respiration– Modified anatomy– Active Metabolism– Vision

Active Metabolism• Flight requires lots of energy and as such birds

need an active metabolism• As such birds are endothermic– Use their own metabolism to regulate body heat

• Birds also utilize their feathers to help maintain body temperature– For this reason it is likely feathers were first adapted

as insulation to help maintain body temperature and only later made part of the flight equipment

• In some birds they also have layers of fat to aid in insulation

Feathers

• Evolved from the scales of bird’s reptilian ancestors• Feathers are very light and strong and made of the

protein keratin– Same protein in reptile scales, and mammals hair and nails

• There are different kinds of feathers:– Downy feathers

• Provide insulation by trapping air– Contour feathers

• Are stiff and are key for flight and help give aerodynamic shape

Feathers StructureContour Feather• Are light weight with hollow

main shafts (quills)• Barbs branch from the shaft

and are held in place by hooks– This keeps feathers flat and

aerodynamicDowny Feather• Same as contour, but lack

hooks on the barbule• Gives feather a fluffiness

that aids in insulation role

Wings• Wing are elongated limbs and the way

feathers attach to the wing provides the curved surface needed for lift and thus flight– Wings stretched out illustrate the same principles

of aerodynamics as airplane wings.– Pressure differences created by differences in air

flow over the top and bottom of the convex wing lift the wing and the bird.

Wing Diagram

Skeleton and Muscle• Flight requires large

pectoral muscles to flap the wings– These large muscles

anchor on the large sternum (breastbone)

• Birds bones are light weight, flexible and strong– Bones are honeycombed

to allow for light weight without giving up much strength

More on the Skeleton

• Utilize light weight beaks and have no teeth• Some bones of the skeleton are actually

joined to the lungs– In doing this the air in the bones is warmed by the

body, and it increases the buoyancy of the bird– Recall warm air rises

Respiration• Birds have lungs, but also have air sacs among the internal organs

and inside bones• Air is inhaled by the mouth and nose, down the trachea into the

lungs and air sacs• During exhalation carbon dioxide is expelled and some of the air

from the air sacs enters the lungs– By doing this it makes it so the bird has almost a continuous supply of

fresh air– This also allows birds to breath in the thin air found at higher altitudes

• Thus using this air sac system it helps insure there is adequate oxygen for the high energy requirements of flight, but it also helps increase the birds buoyancy

• Air sac system also makes birds have the most efficient respiratory system of all the chordates

Respiration System

Circulation• So to take advantage of the

strong respiration system the bird also needs a strong circulatory system to insure muscles have adequate oxygen supply

• This is achieved with the 4 chamber heart– 4 chambers insures complete

separation of oxygenated and deoxygenated blood

– This separation helps keeps higher levels of oxygen in blood and a very efficient metabolism to maintain body temperature and energy needs of the bird

Modified Anatomy

• Anatomy in birds is modified in many ways to aid in flight

• You have already seen some (e.g. air sacs) but some other examples are:– Lack urinary bladder• Urine replaced with uric acid, which is excreted with

feces

– Females have one ovary– Use of gizzard instead of teeth for grinding food

Modified Anatomya) Small contour feathers provide

streamlined body shapeb) Long, broad primary feathers

provide large surface area to catch air and give maximum lift

c) Hollow quill gives maximum strength with little weight

d) Interlocking projections provide large, flat airfoil that provides lift

e) Long tail feathers act as rudder, controlling flight direction

f) Small pebbles held in gizzard grind food

g) Air sacs attached to lung help take in large volume of air

h) Crop stores food

Vision and Hearing

• Flight requires excellent vision and hearing– Have acute colour vision

• Both aid in flight, but also help birds in getting the food they need for the energy toll of flight

Advantages of Flight• Improved hunting and

scavenging– E.g. allows bird to exploit

flying insects• Allows escape form

earthbound predators• Allows birds to move

great distance– Makes possible seasonal

migrations to exploit different food resources and seasonal breeding areas

Reproduction• Birds have elaborate courtships

rituals– Songs– Displays– Dances

• As you all know birds lay eggs– Fertilization is internal

• Embryos in the eggs are kept warm through brooding (sitting on) by the mother, father or both depending on the species

• Young are taken care of by one or both parents until the times comes for them to leave the nest– Length of time varies between bird

species

Homework

• Read pages461-465

• Answer Questions:– 1-4 page 465