21-AEBI212- Birds and Migration

Characteristics of Birds (Class aves!)

Feathers

Forelimbs modified into wings

Hind limbs for walkings, swimming, or perching

Keratinized beaks and feathers

oviparous

What are two groups of living birds?

Paleognathae (ancient+ jaw) and Neognathae (new + jaw)

Paleognathae

Large, flightless birds

Flat sternum with poorly developed pectortal muscle

(Ostrich, Kiwi)

Neognathae

All other birds

Keeled sternum with powerful flight muscles

Nearly all fly (except penguins, they ‘fly” underwater)

Arboreal theory for flight evolution

Ancestors climbed to high places (trees) and glided down

Cursorial Theory for flight evolution

Ancestors flapped their wings to launch into air from ground (cursorial=adapted for running)

Adaptations for flight

• wings for lift and propulsion

• bones light + rigid

• Efficient respiratory system (intense metabolic demands)

• Rapid and efficient digestive system

• Energy-rich diet

• High-pressure circulatory system

What do feathers play a role in?

Mating, Territorial Dominance, Body temp regulation (insulation+ waterproofing), Camoflage, fight

Shaft

made up of calamus and rachis

Vanes:

soft surfaces of the feather on either side of the rachis

Barbs

Emerge from rachis(upper shaft): arranged in parallel and spread diagonally outwards

Barbules

Emerge from each barb and can the barbs together

Pennaceous feathers

Interlocking barbules: stiff, flat, waterproof

Plumaceous Feathers

Loosely arranged barbules: fluffy, downy, warm

Can feathers have both pennaceous and plumaceous regions?

Yes!

Contour feathers

The outermost feathers: gives bird its form. Incl: Wing feathers, tail feathers, and coverts

Semiplumes

beneath contour feathers: developed rachis, BUT no hooks on barbules

Down

beneath contour feathers: soft tufts without a rachis

Contour feathers- Remiges

Wing feathers

Asymmetrical vanes

Attached by ligaments or directly to the bone

Contour feathers- Rectrices

Tail feathers

Symmetrical vanes

Attached to each other by ligaments

Only innermost are attached to tailbone

Contour feathers- Coverts

Small contour feathers that cover and border remiges and retrices

Help shape the wing & give insulation

Molting in Birds

Most birds can fly unimpaired during molting (remiges and rectrices molted in pairs for balance)

Water birds lose all primary feathers at same time, can’t fly

Why is timing critical for molting in birds?

It takes a lot of energy

Usually druing periods with lower energy demands (eg. after nesting, season with abundance of food)

How does plumage change with molt?

Winter (nonbreeding) plumage

Summer (breeding) plumage

Juvenile/adult plumage

Why are bird skeletons light and delicate but sturdy?

many bones are pneumatized (hollow), laced with air cavities

skull

light, mostly fused into one piece. Less bones than other tetrapod skulls

Jaw

light, lacks teeth (grinding like a gizzard)

Keratinous beak

molded around jaw- jaw mobility allows for wide gape

Which is heavier, bird skeleton or similarly sized mammal skeleton?

Neither! Similar weight, different distribution

How is weight distributed in birds?

skull and wings= light, legs= heavy. Lower center of gravity= good aerodynamic stability

What are skeletal adaptations for flight?

Vertebrae (except neck) fused together

Sternum having large thin keel (reduced in flightless birds)

Bones of forelimbs reduced in number and fused together

What is the point of bird sternum having large thin keel

Functions as point of attachment for powerful flight muscles

What are the pectoralis and supracoracoideus muscle attached to? How big are they compared to other muscles?

The keel of the sternum. These locomotor muscles are way bigger than other muscles

What does the pectoralis muscle do? How big is it?

Depresses the wings in flight. Largest muscle

What does the supracoideus muscle do? Where is it located

it raises the wing through “rope and pulley” arrangement. Located between pectoralis and the sternum and also attached to humerus by a tendon.

What is the most efficient respiratory system of any terrestrial vertebrate?

That of the birds!

Where are the air sacs in a bird? What are they connected to?

Throughout thorax and abdomen, inside bones. Connected to the lungs

Describe continuous flow

Continuous flow of oxygen through lungs. 2 cycles for single reath to pass through system

Alveoli

small sacs surrounded by capillaries, site of gas exchange in mammals

Parabronchi

tubelike structure in birds homologous to alveoli in mammals