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Biology
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31-2 Birds
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3. Nonvertebrate chordates
Phylogeny of Chordates
Mammals
Birds
Reptiles
Amphibians
Bony fishes
Sharks
& their relatives
Jawless fishes
Nonvertebrate chordates
Although nonvertebrate chordates lack a vertebral column, they share a common ancestor with vertebrates.
Invertebrate ancestor
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What Is a Bird?
What Is a Bird?
Birds are reptile like animals that maintain a constant internal body temperature;
Outer covering of feathers;
two legs that are covered with scales and are used for walking or perching;
front limbs modified into wings.
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The single most important characteristic that separates birds from reptiles and other living animals is feathers.
Feathers are made mostly of protein and develop from pits in the bird’s skin.
- Feathers help birds fly and keep them warm.
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What Is a Bird?
Feathers
two main types of feathers are contour and down.
Barb
Contour feather: Contour feathers provide the lifting force and balance needed for flight.
Birds have different types of feathers that vary in structure and function. An outer covering of feathers is the main characteristic that sets birds apart from other animals.
Barbule: The hooks on each barbule fit together, holding them flat.
Down feather: Down feathers trap air close to the body and keep the bird warm.
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7. Form, Function, and Flight
Form, Function, and Flight p
Adaptations for flight:
aerodynamic feathers and wings
strong, lightweight bones
strong chest muscles
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8. Form, Function, and Flight
Body Temperature Control  p808
Birds can generate their own body heat.
Animals that can generate their own body heat are called endotherms.
Endotherms include birds, mammals and some other animals.
Endotherms have a high rate of metabolism as compared to ectotherms. Metabolism creates heat.
Body temp of a bird is about 41 degrees C.
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Feeding
Birds eat a lot relative to their size.
The phrase “eats like a bird” is misleading.
Birds bills or peaks are adapted to the type of food they eat. For example:
Birds eating insects have short fine bills
Birds eating seeds have short thick bills.
Long thin bills can be used for gathering nectar from flowers or probing soft mud for worms and shellfish.
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Feeding
Digestive system of a bird:
bill, mouth
esophagus
crop
two part stomach which includes the gizzard.
liver
gallbladder
pancreas
small intestine
large intestine, cloaca
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11. Form, Function, and Flight
Esophagus
Crop
When a bird eats, food moves down the esophagus and is stored in the crop.
Birds have a number of adaptations that enable them to fly, including an efficient digestive system.
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12. Form, Function, and Flight
First chamber of stomach
Gizzard
Moistened food passes to the stomach, a two-part chamber.
Birds have a number of adaptations that enable them to fly, including an efficient digestive system.
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13. Form, Function, and Flight
Birds have a number of adaptations that enable them to fly, including an efficient digestive system.
Large intestine
Small intestine
As digestion continues, the food moves through the intestines.
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14. Form, Function, and Flight
Birds have a number of adaptations that enable them to fly, including an efficient digestive system.
Undigested food is expelled through the cloaca
Cloaca
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Respiration
When a bird inhales most air first enters large posterior air sacs in the body cavity and bones.
The inhaled air then moves through the lungs in a series of small tubes. These tubes are lined with specialized tissue, where gas exchange takes place.
The complex system of air sacs and breathing tubes ensures that air flows into the air sacs and out through the lungs in a single direction.
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16. Form, Function, and Flight
Respiration
Air flows in a single direction.
The one-way flow of air:
constantly exposes the lungs to oxygen-rich air.
maintains a high metabolic rate.
provides efficient extraction of oxygen, which enables birds to fly at high altitudes where the air is thin (oxygen poor).
Most land vertebrates including us have a two way air flow system. We breath in oxygenated air and breath out oxygen poor air.
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How does birds respiratory system differ from that of most land vertebrates?
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Circulation
Birds have a 4 chambered heart (like us) and two separate circulatory loops.
There is complete separation of oxygen-rich and oxygen-poor blood.
One half of the heart receives oxygen rich blood and the other half of the heart receives oxygen poor blood.
This double-loop system ensures that oxygen collected by the lungs is distributed to the body tissue with maximum efficiency.
loop 1
loop 2
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Draw a 4 chambered heart with the two loops.
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20. Form, Function, and Flight
Excretion  
Excretion in birds is similar to that of reptiles.
Nitrogenous wastes are removed from the blood by the kidneys, converted to uric acid, and deposited in the cloaca.
Most of the water is reabsorbed, leaving uric acid crystals in a white, pasty form.
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Response
Birds have well developed sense organs.
Birds have a brain that can quickly interpret and respond to a lot of incoming signals. A bird’s brain is relatively large for its body size.
Cerebrum is large – controls behaviors such as flying, nest building, care of young, courtship and mating.
Cerebellum is also well developed – required for precise coordinated mov’ts
(cerebrum)
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Response
Medulla oblongata – coordinates basic body processes, such as the heart beat
Eyes are well developed and the optic lobes in the brain are well developed. Birds can see colors.
Birds can hear quite well.
Sense of taste and smell are not well developed in most birds – the olfactory bulbs in a bird’s brain are small.
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Video Crows are smart (2min):
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Movement
Some birds can not fly. Instead they get around by walking or running – ex. Ostriches or by swimming like penguins.
Observe a birds skeleton.
What is the skeletal difference btw a bird that can fly and one that can not?
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25. Form, Function, and Flight
Skeletal System of a Bird
Skull
Vertebra
Pelvic girdle
Collarbone (wishbone)
Strut
Tailbone
Like most of its anatomy, a bird’s skeleton is well adapted for flight, providing a sturdy attachment point for muscles. The long bones are exceptionally strong and light because of cross-bracing and air spaces. In strong flying birds, such as pigeons, the chest muscles may account for as much as 30 percent of the animal’s mass. 
Pectoral griddle
Air space
Sternum
Rib cage
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26. Form, Function, and Flight
Bones are strengthened by struts.
Air spaces make bones lightweight. . 
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Reproduction p812
Male and female reproductive tracts open into the cloaca.
Mating birds press their cloacas together to transfer sperm from the male to the female.
Some male birds have a penis that transfers sperm to the female’s cloaca.
Birds eggs are amniotic eggs. Most birds incubate their eggs until the eggs hatch.
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Reproduction
When the chick is ready to hatch, it uses a small tooth on its bill to make a hole in the shell.
Chicks are born with feathers.
Both parents may be involved in feeding the chick.
Do birds have internal or external fertilization?
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Groups of Birds p812
30 different Orders of birds
(Kingdom Animalia, Phylum Chordata, Class Aves – class Aves is split into 30 different Orders)
Figure Overview some of the types of birds:
pelicans and their relatives, parrots, birds of prey, perching birds, cavity-nesting birds, herons and their relatives, ostriches and their relatives.
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Ecology of Birds p814
B/c birds are so diverse and numerous they interact with natural ecosystems in different ways. Examples:
Hummingbirds pollinate flowers.
Fruit eating birds swallow seeds but do not digest them, so their droppings disperse seeds over great distances.
Insect eating birds control the population of bugs such as mosquitos.
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List 2 other ways in which birds interact with natural ecosystems.
Read Chapter 31 and do all of the assessment questions at the end of the chapter.
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31-2
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31-2
A bird with a short, thick bill probably eats
fish.
seeds.
insects.
fleshy fruit.
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31-2
Archaeopteryx has characteristics of both
modern birds and ancient birds.
amphibians and reptiles.
reptiles and modern birds.
amphibians and modern birds.
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31-2
Which of the following bird adaptations is NOT associated with flight?
bones with many hollow air spaces
air sacs in addition to lungs
gizzard
contour feathers
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31-2
Which of the following birds assists in pollinating flowering plants?
pelican
hummingbird
raptor
heron
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37. END OF SECTION