Ornithology Exam 1

• Birds are conspicuous & easily observed

• Their dominant senses (sight and hearing) are our dominant senses (which makes them easy for us to study)

Why have bird studies contributed so much to biology?

Wing feathers (remiges)

specialized for flight are characterized by uniform windproof surfaces on either side of the central shaft that are created by an interlocking microstructure

asymmetric with a shorter, less flexible leading edge that prevents mid-air twisting

Tail feathers (rectrices)

feature an interlocking microstructure similar to wing feathers. Arranged in a fan shape, support precision steering in flight.

In some birds they have evolved into showy ornaments

Contour feathers (coverts)

what you see covering the bird’s body. Arranged in an overlapping pattern like shingles, the waterproof tips are exposed to the elements and the fluffy bases are tucked close to the body.

Sometimes brilliantly colored or uniformly drab, can also help the bird show off or stay camouflaged

shape it into an efficient airfoil by smoothing over the region where the flight feathers attach to the bone.

Semiplume

Mostly hidden beneath other feathers on the body

have a developed central rachis but no hooks on the barbules, creating a fluffy insulating structure

Down

Similar to semiplumes with a loosely branching structure but little or no central rachis

relatively short and positioned closest to the body where they trap body heat

Filoplume

Short simple feathers with few barbs

function like mammal whiskers to sense the position of the contour feathers

Bristle

simplest feathers, with a stiff rachis that usually lacks barb branches

Most commonly found on the head, may protect the bird’s eyes and face

Pennaceous feathers

stiff and mostly flat, a big difference that comes from a small alteration in structure; microscopic hooks on the barbules that interlock to form a wind and waterproof barrier that allows birds to fly and stay dry

• Flight

• Insulation

• Mate attraction & camouflage

• Waterproofing

Feathers play critical roles in…

1. The earliest feather was a simple hollow tube.

2. The simple tube evolved into a cluster of barbs.

3. a) The base of the barbs fused together to form a central rachis and b) barbules branched from the barbs.

4. The barbules evolved hooks that interlock.

5. The feather structure evolved asymmetry.

Evolutionary stages of feathers

1. Distribution of mass

2. Weight loss

3. Fusion of bones

Anatomy shaped by flight in 3 major ways

Under wings

Where are flight muscles are distributed?

~15% of bird weight

Muscles associated w/flight constitute

• Mass reduced distally

  • No heavy heads

    • No heavy teeth

  • Muscles of appendages located near center of gravity

How mass is redistributed

Pectoralis major

• Largest muscle

• Contraction pulls wings down

• Attached to keel & ventral side of humerus

Pectoralis minor (supracoracoideus)

• Contraction pulls wings up

• Attached to keel & dorsal side of humerus

Triosseal canal

• Pulley that allows supracoracoideus to pull wing up from below

• At the intersection of coracoid, scapula, and humerus

Furcula (fused clavicles; wishbone)

Flexes w/ wingbeats; may help facilitate air exchange in air sacs

• No teeth

• Pneumatic bones (maximizes strength relative to bone mass and volume)

• Reproductive organs shrink during non-breeding seasons

• Rapid digestion, wastes voided before flight

Ways birds stay lightweight

Rigid airframe

Save energy by promoting more efficient flight

Handles stresses of flight

Bones principally fused in thoracic & pelvic regions

Thoracic vertebrae

Spinous processes fused; notarium

Synsacrum

• Lumbar, sacral, some caudal vertebrae, & associated ribs, are fused with the pelvis

• Deals w/ stresses of take-offs, (landings), and forces on the tail; reduces need for back muscles

Uncinate processes

• Projections off ribs that provide overlap

• Makes the rib-cage a rigid frame

plumulaceous

having soft, separated barbs

barbs

fused barbules

papilla

small outgrowth of skin where feathers grow

rachis

fused barbs

Insulation

What were feathers originally hypothesized to be evolved for?

Preening

Daily feather maintenance

• Cleans

• Waterproofs

• Keeps flexible

• Reduces fungal and bacterial load

Purposes of preen gland oils

Plumage

total feather coat

Basic or winter plumage

molt after breeding

Alternate or nuptial/breeding plumage

molt before breeding

• Obtaining food

• Limited processing of food

Beak/bill functions

• Size & shape (e.g. straight or curved)

• Serrations, hooks, & cutting edges

• Generalists vs specialists

Beak/bill modifications

Mucous glands

for moistening food & for food itself

Esophagus

tube leading to stomach

Crop

(stores food), not present in all

pigeon crop milk feeds young

Proventriculus

produces powerful digestive enzymes that initiate chemical digestion

Gizzard

grinds food (mechanical digestion)

Small intestine

food molecules absorbed into bloodstream

Ceca

Aids in digestion of plant material due to presence of bacteria

Large intestine

Absorb water and store waste prior to release

Cloaca

Receives waste products

• Gleaning (ground, bark, & foliage)

• Hawking

• Aerial foraging & aerial pursuit

• Patroling

• Probing

• Diving, dipping, & dabbling

• Stalking & striking

Modes of feeding

Optimal foraging theory

“In theory, when a bird uses the smallest amount of energy to gather high-energy, nutritional food, optimal foraging is occurring.”

Feeding ecology

Responses to variation in food abundance varies depending on degree of specialization

Lift

facilitated by movement of air over an airfoil

can be increased by increasing the ‘angle of attack’

Downstroke

• Secondaries primarily move down

• Primaries move down and forward

Upstroke

• Secondaries primarily move up

• Primaries move up and back

Wing loading

bird mass/wing surface

the factor that limits the ultimate size of birds that fly

Aspect ratio

ratio of length/width; a means to describe wing shape

• High = long, narrow wings

• Low = short, broad wings

Thermal soaring

Stay on top of rising thermals

Gain altitude and glide down to next thermal

Slope / obstruction soaring

Take advantage of up-drafts & pressure differences as air flow encounters ridges or other obstructions

metabolism

All the chemical processes that occur within an organism’s cells

• Heat released due to chemical reactions

• Rate of metabolic processes ⬆ w/temp

Two important aspects of metabolism

• Speed of nerve signal increase 1.8 x

• Speed & strength of muscle contractions increase 3 x

With every 10º C increase in body temperature…

• Down feathers (coupled w/posture)

• Shelter (particularly from wind)

• Communal roosting

• Counter-current heat exchange

• Torpor

How birds cope with cold

• Avoidance behaviors

• Evaporative cooling through panting

• By-pass counter-current network

• Hyperthermy

How birds cope with heat