Birds

Question 1

What are birds?

Answer 1

• Class Aves
• Approx 10,000 species
• Unique feature: feathers
  All birds have feathers, and all animals that have feathers are birds

Question 2

What are characteristics of all birds?

Answer 2

• General uniformity of structure compared to other taxa
  Flight restricts morphological diversity
• Feathers
• Forelimbs modified into wings
  Not always used for flight
• Hindlimbs adapted for walking, swimming or perching
• Keratinized beaks and feathers
• Oviparous

Question 3

What are their origins and relationships?

Answer 3

• Birds evolved from theropod dinosaurs
• Archaeopteryx (transitional between feathered dinosaurs and modern birds)
• May have been able to fly or glide

Question 4

What are the two groups of living birds?

Answer 4

Paleognathae

Neognathae

Question 5

What is Paleognathae?

Answer 5

• Large flightless birds

- Flat sternum with poorly developed pectoral muscles

Question 6

What is Neognathae?

Answer 6

• All other birds
• Nearly all fly
  Penguins are flightless (although they use their wings to ‘fly’ underwater)
• Keeled sternum with powerful flight muscles

Question 7

How is their flight?

Answer 7

• Two competing theories
  Arboreal Theory: Ancestors climbed to high places (trees) and glided down
  Cursorial Theory: Ancestors flapped their wings to launch into air from ground (cursorial = adapted for running)

Question 8

Explain the arboreal hypothesis

Answer 8

• Thought to be most likely
• Evidence: extant flightless species which can glide
• Modifications for lift and powered flight would come later
• Weakness: few feathered dinosaurs were arboreal

Question 9

Explain the cursorial hypothesis

Answer 9

• Generally considered less likely
• Evidence: chukar partridge chicks use wingbeats to assist running up steep inclines
• Weakness: difficult to overcome gravity

Question 10

What are their adaptations for flight?

Answer 10

• Wings for lift and propulsion
• Bones light yet rigid
• Respiratory system highly efficient
  Intense metabolic demands
• Rapid and efficient digestive system
• Energy rich diet
• High pressure circulatory system

Question 11

What are feathers?

Answer 11

• Defining characteristic of birds

- Lightweight but very strong

Question 12

What do feathers have a role in?

Answer 12

• Mating
• Territorial dominance
• Regulation of body temperature
  Insulation abasing heat and cold
  Waterproofing
• Camouflage
• Flight

Question 13

What are the structures to the feathers?

Answer 13

- Made up of four parts:   
    Shaft
    Vanes
    Barbs
    Barbules
- Feathers are assymetrical
- The outer vane is smaller than the inner vane
- The outer vane is the leading edge of the wing

Question 14

Explain shaft

Answer 14

Made up of calamus and rachis

Question 15

Explain vanes

Answer 15

Soft surfaces of the feather (on either side of the rachis)

Question 16

Explain barbs

Answer 16

Emerge from rachis to form vanes (arranged in parallel and spread diagonally outwards)

Question 17

Explain barbules

Answer 17

Emerge from each barb and hold the barbs together

Question 18

What are the types of feathers?

Answer 18

Contour feathers
Down feathers
Filoplumes
Powder downs

Question 19

What are contour feathers?

Answer 19

The outermost feathers that give the bird its form

Question 20

What are down feathers?

Answer 20

• Soft tufts without a prominent rachis

- Beneath contour feathers

Question 21

What are filoplumes?

Answer 21

• Hairlike feathers

- Function not known

Question 22

What are powder downs?

Answer 22

• Tips disintegrate as they grow releasing a talc like powder
• Helps to waterproof feathers
• Characteristic of herons, bitterns, hawks and parrots

Question 23

What are the types of contour feathers?

Answer 23

Remiges
Retrices
Coverts

Question 24

What are remiges?

Answer 24

• Flight feathers
• Often largest contour feathers
• Attached by ligaments or directly to the bone

Question 25

What are retrices?

Answer 25

• Tail feathers
• Attached to each other by ligaments
• Only innermost are attached to the tailbone

Question 26

What are coverts?

Answer 26

• Small feathers that overlay and border remiges and retrices
• Help shape the wing and provide insulation

Question 27

Explain the molt in birds

Answer 27

• Feathers are dead
  Like hair or nails in humans
  Cant heal when damaged
• Periodically shed and replaced (or molted)
• Most birds molt feathers gradually
  One exception is penguins (molt all feathers at once)
• Remiges and retrices are molted in pairs, to maintain balance
• Most (but not all birds) can fly unimpaired during molting
• Water birds lose all primary feathers at the same time (can’t fly during this period)
• Molt takes energy
  Timing critical
  Usually seasonally during periods with lower energy demands (immediately after nesting and season when food is abundant)
• Plumage can change with molt
  Winter (non breeding) plumage
  Summer (breeding) plumage
  Juvenile/adult plumage

Question 28

How are their skeleton?

Answer 28

• Light and delicate (but sturdy) skeleton
• Many bones are hollow (pneumatized)
• Laced with air cavities
• Skull lightly built and mostly fused into one piece
  Less bones than other tetrapod skulls
• Jaw lightly built (lacks teeth)
  Grinding function of gizzard
• Keratinous beak molded around jaw
  Jaw is quite mobile (gaped widely)
  Most birds have kinetic skulls (as discussed for lizards and snakes)
  However the entire skull of snakes and lizards is kinetic as compared to bird where it is fused

Question 29

How is their skeleton adapted for flight?

Answer 29

• Weight of bird skeleton and similarly sized mammal skeleton are comparable
• Distribution of weight is different
  Skull and wings are very light
  Legs are heavier
• Lowers centre of gravity of bird and improves aerodynamic stability
• Vertebrae are fused together (except for neck)
• Sternum has a large, thin keel
  Provides point of attachment for powerful flight muscles
  Keel is reduced in flightless birds
• Bones of forelimbs are highly modified for flight
  Reduced in number and fused together

Question 30

How is their muscular system?

Answer 30

• The locomotor muscles are massive compared to other muscles
• The pectoralis and supracoracoideus muscle are both attached to the keel of the sternum
• The pectoralis muscle depresses the wings in flight
  Largest muscle
• The supracoracoideus muscle raise the wing
  Is not attached on the backbone
  It is located between the pectoralis and the sternum
  It is able to pull the wing up because of an elegant “rope and pulley” arrangement
  Attached to the upper wing bone (humerus) by the tendon
• Tendons extend into the toes from the leg muscles
• No muscles in the foot
  Makes feet resistant to freezing
• When a bird settles on a perch the tendons tighten automatically
  Prevents bird from falling off while asleep

Question 31

How is their respiratory system?

Answer 31

• Most efficient respiratory system if any terrestrial vertebrate
  Unique in animal kingdom
• Air sacs
  Throughout thorax and abdomen
  Even inside of bones
  Connected to the lungs
• Continuous flow
  Takes two cycles for a single breath to pass throughout the system
  Continuous flow of oxygen through lungs

Question 32

What are aveoli?

Answer 32

Small sacs surrounded by capillaries, where gas exchange takes place in mammals

Question 33

What are parabronchi?

Answer 33

Tubelike structure in birds homologous to aveoli in mammals

Question 34

Explain their respiratory system in more detail

Answer 34

• Air sacs connect to the lungs in such a way that most of the inspired air bypasses the lungs and flows directly into the posterior air sacs, which serve as reservoirs for fresh air
• On expiration, this oxygenated air is passed through the lungs and collected in the anterior air sacs
• From there it flows directly to the outside
• Thus, it takes two respiratory cycles for a single breath of air to pass through the respiratory system