The Bird Body

Characteristics of Birds

• All birds are members of the class Aves• Birds have retained some reptilian

characteristics – Amniotic eggs – Feet and legs of birds are covered in scales

Characteristics of Birds

• All birds share similar characteristics:– Feathers that cover the body– Wings – Lightweight skeleton– Endothermic metabolism (warm-blooded) – Lungs with air sacs– A Beak

Body Temperature and Control

• Birds are endothermic – They generate enough heat through metabolism to

maintain a high body temperature – Their environment does not determine body temp.

• Normal body temp. is 40-44 degrees Celsius – Body temp is significantly higher than mammals body

temp (37 degrees Celsius)

• Birds have high body temp. due to a fast metabolism

Energy to Fly

• A quick and efficient digestive system allows birds to obtain enough energy to fly and maintain their body heat – Some eat up to ½ their body weight in a day

• Food passes quickly through the digestive system– Ex. A Thrush can eat blackberries, digest the, and

excrete the seed 45 minutes later• It would take humans 12 hours

Adaptations for Birds

• Flight requires a number of special adaptations – Feathers– A strong, lightweight skeleton

• Other adaptations include: – A bird’s beak and feet– Both are adapted to the food the bird eats and the

environment they live in

Feathers

• Birds have two main types of feathers 1. Contour Feathers

2. Down Feathers

Contour Feathers

• Contour Feathers cover an adult bird’s body– Contour feathers on the tails and wings are called

flight feathers, and provide lift for flight – Contour feathers have many branches called

barbs– Barbs are linked together giving the feather a:• smooth surface • sturdy flexible shape

Contour Feathers

Down Feathers

• Down Feathers cover the body of young birds and are found beneath adult bird’s contour feathers

• Down Feathers trap warm air and conserve body heat

Lightweight Skeleton

• Bones of birds are thin and hallow• Many of the bones are fused– More rigid skeleton than reptiles – Creates a sturdy frame that anchors muscles

during flight

Breastbone and Muscles • Power of flight comes from the large breast

muscle – Makes up 30% of a bird’s weight – Muscles stretch from the wing to the breastbone

• The breastbone is very large and bears a prominent keel– Keel resembles the v-shape bottom of a boat

• Muscles are attached to the keel and to the fused collarbones – **NO other vertebrates have fused collarbones or a

keeled breastbone**

Keel Shaped Breastbone

Beaks and Feet

• Birds are adapted for different ways of life• You can learn a great deal about a bird’s diet

and habits by examining the bird’s beak, feet, and legs

Perching and Flightless Birds

• Feet: – Perching birds:• Have curved toes for holding onto branches

– Flightless birds: • Have strong legs and feet with thick toes that are

modified for running

Perching and Flightless Birds

• Beaks: – Perching Birds:• May be short and thick, which allows crushing of

seedsEx. Canary

• Long, thin, beaks for drinking nectar Ex. Humming birds

• Long, strong beaks for snatching insects out of the air

Ex. Woodpeckers

Marsh Birds and Water Birds

• Feet:– Marsh Birds: • Have long toes that keep them from sinking into the

mud• Have long legs to keep the bird’s body above water • Very clumsy when they try to land in trees

– Water Birds: • Webbed feet – used for paddling• Have trouble perching in trees

Marsh Birds and Water Birds

• Beaks: – Marsh Birds:• long beaks for catching fish or digging in mud for

worms

– Water Birds:• Rounded beaks for eating plants • Long beaks for eating fish• Hooked beaks to grip slippery prey• Sharp beaks used to spear fish

Review Questions

• 1. Summarize how birds obtain the energy necessary for flight

• 2. Identify a bird’s adaptations for flight • 3. Write a paragraph (3/4 of a page long)

about the following– Some biologists have proposed that birds and

reptiles should be grouped in the same class of vertebrates. Do you Agree? Support your answer with at least 5 reasons.

Respiration and Circulation

• The following respiratory and circulatory structures help all birds obtain the energy they need– Air sacs– Four chambered heart

• They also improve oxygen intake and delivery

Air Sacs

• Birds have air pass over the lung surface’s in one direction– Air sacs allow one-way air flow– Air sacs act as holding tanks for air

• Advantages to one-way air flow 1. Lungs only exposed to fresh air, increasing

the amount of oxygen that can be absorbed2. Blood and air can flow in different directions,

allows increase in oxygen absorption

Four- Chambered Heart

• Blood enters the right atrium• Specialized tissue lies in the muscular wall of

the right atrium – Heartbeat originates in this tissue– Tissue known as the pacemaker

• A bird’s heart rate can be extremely high in order to pump large amounts of oxygen to the bird’s body

Four- Chambered Heart Structure

• Ventricle is divided into a right and left by the septum

• Allows oxygen rich and oxygen poor blood to remain separate – Allows oxygen to be delivered to the body cells

more efficiently

Reproduction

• Reproduce through internal fertilization• During mating male birds press their cloaca to

the female’s cloaca and releases sperm• Produces amniotic eggs– May lay one egg or a clutch of several eggs

Parental Care

• Most birds care for their eggs and their young• Birds usually lay their eggs in nests– Hold eggs and conceal them from predators and

other elements – Nests are built from available materials • Twigs, barks, grasses, feathers…etc.

• One or both of the parents warm, or incubate, the egg by sitting on them

Bird Mating

• Most species of birds form pairs that are made up of male and female – May spend their entire lives together and defend

a single territory

• However, eggs may be fertilized by several different fathers– Usually leads to extensive parental care

Parental Care

• Three options for parental care1. Only one parent takes care of the egg

Ex. African Jacana

2. Caring for hatchling is an affair for the entire family (parents, siblings, …etc).

3. No care for the youngEx. Brown-headed Cowbirds will lay their eggs in other bird’s

nests and let other birds raise their young

Review Questions

• 1. Explain the functions of the anterior and poster air sacs

• 2. In paragraph form Describe reproduction and parental care in birds

• 3. Why is it advantageous for birds to be oviparous rather than ovoviviparous? What’s the difference between oviparous and ovoviviparous?