Lecture 20 Flashcards
Characteristics of all Birds
- Flight restricts morphological diversity
- Feathers
- Forelimbs modified into wings
- Hindlimbs adapted for walking, swimming, or perching
- Keratinized beaks and feathers
- oviparous
Origins and Relationships of birds
- Birds evolved from theropod dinosaurs
- Archaeopteryx – transitional between feathered dinosaurs and modern birds
- May have been able to fly or glide
Two Groups of Living Birds
Paleognathae (Greek palaios, ancient + gnathos, jaw)
• Large flightless birds
• E.g. Ostrich, kiwi
• Flat sternum with poorly developed pectoral muscles
Neognathae (Greek, noes, new + gnathos, jaw)
• All other birds
• Nearly all fly
• Penguins are flightless (although they use their wings to ‘fly’
underwater)
• Keeled sternum with powerful flight muscles
Flight evolution theories
- Arboreal Theory: Ancestors climbed to high places (e.g. trees) and glided down
- Cursorial Theory: Ancestors flapped their wings to launch into air from ground
• Cursorial = adapted for running
Which flight evolution theory is most likely
• Arboreal hypothesis thought to be most likely
• Evidence: extant flightless species which can glide
• e.g. kakapo, flightless New Zealand parrot
• modifications for lift and powered flight would come
later
• Weakness: few feathered dinosaurs were arboreal
- Cursorial hypothesis generally considered less likely
- Evidence: chukar partridge chicks use wingbeats to assist running up steep inclines
- Weakness: difficult to overcome gravity
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
Feathers characteristics
• Defining characteristic of birds • Lightweight but very strong Roles in • Mating • Territorial Dominance • Regulation of body temperature • Insulation against heat and cold • waterproofing • Camouflage • Flight
Feather Structure
- Shaft: made up of calamus and rachis
- Vanes: soft surfaces of the feather, asymetrical on either side of the rachis
- Barbs: emerge from rachis to form vanes
- arranged in parallel and spread diagonally outwards.
- Barbules: emerge from each barb and hold the barbs together
Feather asymmetry
• Feathers are assymetrical
• The outer vane is smaller
than the inner vane
• The outer vane is the leading edge of the wing
Types of Feathers
Contour feathers
• the outermost feathers that give the bird its form
- Down feathers
- soft tufts without a prominent rachis • beneath contour feathers
- Filoplumes
- Hairlike feathers (“hairs” of a plucked bird) • Function not known
- Powder downs
- Tips disintegrate as they grow releasing a talc-like powder • Helps to waterproof feathers
- Characteristic of herons, bitterns, hawks and parrots
Types of contour feathers
Remiges
• Flight feathers
• Often largest contour feathers
• Attached by ligaments or directly to the bone
Retrices
• Tail feathers
• Attached to each other by ligaments
• Only innermost are attached to the tailbone
Coverts
• Small feathers that overlay and border reminges and retrices
• Help shape the wing and provide insulation
Molt in Birds
- Feathers are dead
- Can’t heal when damaged
- Molt takes energy
- Plumage can change with molt
Bird 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
- lacks teeth, grinding function of gizzard
- Keratinous beak molded around jaw
- Most birds have kinetic skulls
- However the entire skull of snakes and lizards is kinetic as compared to bird where it is fused
Skeleton – Adaptations for Flight
- Distribution of weight is different in birds than mammals
- Lowers center of gravity of bird and improves aerodynamic stability
- Sternum has a large, thin keel
Vertebrae are fused together
• Bones of forelimbs are highly modified for flight
Muscular System birds
- The locomoter 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
- The supracoracoideus muscle raises the wing
