Birds

Chapter 42

Origin and Evolution of Birds

Section 42.1

Important characteristics

Feathers – only birds have them!

Wings – modified forelimbs

Lightweight, rigid skeleton – hollow bones

Endothermic metabolism – 104-106o F

Unique respiratory system – most efficient

Beak – no teeth

Oviparity – eggs incubated by parents

Evolution

Similarities to dinosaurs:– Flexible, S-shaped neck– Unique ankle joint– Hollow bones

Birds evolved from small, fast-running carnivorous dinosaurs

Oldest bird fossil - Archaeopteryx

Archaeopteryx

Jurassic period – 150 million years ago

Similar to modern birds because:– Hollow bones

– Furcula: fused collarbone (aka wishbone)

– Feathers

Similar to dinosaurs because:– Teeth

– Claws on forelimb

– Long, boney tail

Origin of flight

Two major hypotheses:1. Ancestors were tree dwellers that ran

along branches and jumped from tree to tree, gliding wings first evolved then the ability to flap came later.

2. Ancestors were land dwellers that leapt after their prey, wings served to trap or knock down prey and over time became large enough to fly.

Feathers

Modified scales

Two main functions:– Provide lift for flight

– Conserve body heat

Types of feathers:– Down feathers – insulation

– Contour feathers – streamline shape, coloration, insulation

– Flight feathers – on wings and tail for flight

Parts of a feather

Structure of the feather

Follicles: tiny pits that feather develops fromShaft: emerges from the follicleVanes: 2 vanes on opposite side of shaftBarbs: branches of the vaneBarbules: projections on the barbs with microscopic hooksKeratin: protein that makes up the feather

Care of feathers

Preening: use beak to rub feathers with oil secreted by the preen gland at the base of the tail.

Molting or shedding of feathers periodically

Characteristics of Birds

Section 42.2

Skeleton & Muscles

Thin, hollow bones fused together

Sternum: breastbone is attachment point for flight muscles

Pygostyle: last fused vertebrae that supports the tail feathers

Flight muscles account for 50% of bird’s weight

Metabolism

Endothermic therefore require large quantities of food to generate heat

Aquatic birds have a layer of fat to insulate

Cannot go through long periods of time without food

Digestive & Excretory Systems

Path of food: mouth esophagus crop 2-part stomach (proventriculus & gizzard) small intenstine with bile from liver large intestine cloaca vent

Path of wastes: blood kidneys ureters cloaca (mixes with feces) vent

Digestive System

Respiratory System

Highly efficientPath of air: nostrils trachea branched bronchi lungs (25%) or air sacs (75%) Air sacs:– 9 total– Stores excess air– Allows for oxygenated air in lungs during

exhale and inhale

Respiratory System

Circulatory System

Rapid heartbeat– Up to 1000 beats per minute!

4 chambered heart– Like mammals

Nervous System & Sense Organs

Large brains (relative to body size)

Some birds have color vision and/or binocular vision

Some birds have a developed sense of smell

Sense of hearing also important

Reproduction

Sperm movement: testies vasa deferentia cloaca female’s cloaca

Egg movement: ovary oviduct fertilized by sperm addition of shell cloaca vent

Nest Building & Parental Care

Lay eggs in nest

Methods of rearing young:– Precocial: active as soon as hatch– Atricial: helpless when born

One or both parents incubate eggs by sitting on them and covering them with their brood patch – Thickened, featherless patch of skin on

abdomen

What type is this?

Migration

Seasonal movement of birds from one habitat to anotherCues to help navigate:– Position of sun and stars– Topographical landmarks– Magnetic field– Air pressure

Ornithologist: biologist that study birds

Classification of Birds

Section 42.3

Diversity

Beak and claws infer diet and habitat

Most widespread terrestrial animal on planet

23 orders of birds

Order Anseriformes

Examples: swans, geese, and ducks

Aquatic

Webbed feet

Flattened bill

Precocial young, care by female

Order Strigiformes

Examples: owls & nocturnal raptors

Sharp, curved beak

Sharp talons

Keen sense of hearing to detect prey

Order Apodiformes

Examples: hummingbirds & swifts

Small, fast-flying

Tiny feet

Long, narrow beak

Order Psittaciformes

Examples: parrots, parakeets, macaws, cockatoos, & cockatiels

Live in the tropics

Strong, hooked beak for opening seeds

Two toes forward, two toes backward for climbing & perching

Highly vocal

Order Picformes

Examples: woodpeckers & toucans

Nest in tree cavities

Diversity of bills based upon diet

Same feet as parrots

Order Passeriformes

Examples: familiar birds (robins, blue jays, cardinals, etc)

perching birds: 3 toes forward, 1 toe backward

songbirds: males produce songs to attract mate and warn away other males– Syrinx produces sound at base of trachea

Order Columbiformes

Examples: pigeons & doves

Plump-breasted, small heads

Short neck, legs, and beak

Crop secretes nutritious milk-like fluid to feed young– Crop milk

Order Ciconiiformes

Examples: herons, storks, raptors, & penguins

World-wide distribution– Habitat determines adaptations

Many are wading birds

Order Galliformes

Examples: turkeys, pheasants, chickens, grouse, & quail

Fowl

Terrestrial birds

Plump-bodies with limited flying ability

Order Struthioniformes

Examples: ostriches & emus

World’s largest birds

Reduction in toe number to allow for fast running