Birds Flashcards
What are birds?
- Class Aves
- Approx 10,000 species
- Unique feature: feathers
All birds have feathers, and all animals that have feathers are birds
What are characteristics of all birds?
- 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
What are their origins and relationships?
- Birds evolved from theropod dinosaurs
- Archaeopteryx (transitional between feathered dinosaurs and modern birds)
- May have been able to fly or glide
What are the two groups of living birds?
Paleognathae
Neognathae
What is Paleognathae?
- Large flightless birds
- Flat sternum with poorly developed pectoral muscles
What is Neognathae?
- All other birds
- Nearly all fly
Penguins are flightless (although they use their wings to ‘fly’ underwater) - Keeled sternum with powerful flight muscles
How is their flight?
- 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)
Explain the arboreal hypothesis
- 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
Explain the cursorial hypothesis
- Generally considered less likely
- Evidence: chukar partridge chicks use wingbeats to assist running up steep inclines
- Weakness: difficult to overcome gravity
What are their adaptations for flight?
- 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
What are feathers?
- Defining characteristic of birds
- Lightweight but very strong
What do feathers have a role in?
- Mating
- Territorial dominance
- Regulation of body temperature
Insulation abasing heat and cold
Waterproofing - Camouflage
- Flight
What are the structures to the feathers?
- 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 wingExplain shaft
Made up of calamus and rachis
Explain vanes
Soft surfaces of the feather (on either side of the rachis)
Explain barbs
Emerge from rachis to form vanes (arranged in parallel and spread diagonally outwards)
Explain barbules
Emerge from each barb and hold the barbs together
What are the types of feathers?
Contour feathers
Down feathers
Filoplumes
Powder downs
What are contour feathers?
The outermost feathers that give the bird its form
What are down feathers?
- Soft tufts without a prominent rachis
- Beneath contour feathers
What are filoplumes?
- Hairlike feathers
- Function not known
What are powder downs?
- Tips disintegrate as they grow releasing a talc like powder
- Helps to waterproof feathers
- Characteristic of herons, bitterns, hawks and parrots
What are the types of contour feathers?
Remiges
Retrices
Coverts
What are remiges?
- Flight feathers
- Often largest contour feathers
- Attached by ligaments or directly to the bone
What are retrices?
- Tail feathers
- Attached to each other by ligaments
- Only innermost are attached to the tailbone
What are coverts?
- Small feathers that overlay and border remiges and retrices
- Help shape the wing and provide insulation
Explain the molt in birds
- 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
How are their skeleton?
- 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
How is their skeleton adapted for flight?
- 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
How is their muscular system?
- 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
How is their respiratory system?
- 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
What are aveoli?
Small sacs surrounded by capillaries, where gas exchange takes place in mammals
What are parabronchi?
Tubelike structure in birds homologous to aveoli in mammals
Explain their respiratory system in more detail
- 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
