Birds

Characteristics• Forelimbs wings• Feathers (of beta keratin, same protein in scales of legs)

• Flight requires lots of energy– Features that reduce weight – Features that increase energy production– Adaptations for flight:

• No urinary bladder• Single ovary • Reduced gonads• Skeletal modifications• One-way respiratory system (w/ parabronchii)• 4 chambered heart (evolved independently of mammal heart)• endothermic

Benefits of flight

• Increased foraging ability• Massive migrations to seasonal food sources• Feeding on airborne insects (new food resource)

• Dispersal• Escape from predators

Keel of sternum (#4)

Furcula (wishbone/collarbone) # 5

Flightless Birds• Ratites

– lack sternal keel– pectoral muscles are reduced/small

– Ostrich (Africa)– Rhea (south America)– Kiwi (new Zealand)– Cassowary (Australia & new guinea and surrounding is.)– Emu (Australia and Tasmania)

Penguins are flightless • But have keel and powerful pectoral muscles because they use

wings to “swim” under water.

Respiratory System• No diaphragm• Air sacs act as bellows• One-way air flow through lungs• Parabronchi• No mixing of residual and fresh air• Counter current like gas exchange

Vocalize w/ Syrinx (not larynx)

membrana tympaniformis

Digestive System

• No teeth• CROP—stores food• Proventriculus—released digestive enzymes• Gizzard (ventriculus)—mixing and mechanical

digestion

EXCRETORY SYSTEM

• Kidneys produce uric acid• No urinary bladder• Ureters connect to digestive track just

upstream of cloaca• Bird “poop” is a mix of feces and uric acid

(white stuff)• They don’t hold it (much) it comes out on

demand

Nervous System

• Flight requires well developed nervous system• Vision– Complex eyes– Large orbit of skull

• Disproportionately large brain– Processing visual information– Integrating sensory and motor function for flight– Intelligent!– Complex behaviors

Reproduction

• Internal fertilization– Cloacal contact (kiss)

• Eggs/oviparous– Adaptation for flight

• Often biparental care• Most birds are monogamous (with lots of cheating)

– Because off spring require so much care—takes both parents– Incubating– Feeding young (young have high energy demand so need lots

of food)– Protecting young