long and weighs less than 0.1 ounce (3
grams). The largest living bird is the
ostrich. Some male ostriches can stand 8
feet (2.5 meters) tall and weigh 300
pounds (135 kilograms).
Feather colors range from drab to very
bright. In many species the male is more
brightly colored than the female. The
female’s dull coloring may help it
remain hidden in the nest. In some
cases, the brightly colored male perches
a short distance away from the nest. In
this way, the male bird draws the attention
of enemies to himself and away
from the eggs and young. The male’s
Many people keep parakeets or
other birds as pets.
There were
no house
sparrows,
starlings, or
domestic
pigeons in
North
America
before Europeans
arrived.
Settlers
brought the
birds from
Europe.
76 Bird BRITANNICA STUDENT ENCYCLOPEDIA
showy coloring may also help it to
attract a mate.
Flight and Basic Structure
Most birds can fly. They are able to do
so because of their body structure and
feathers. Flying birds are strong but
light. Their powerful chest muscles help
them flap their wings. Many of their
bones are hollow, which keeps them
light. Their compact bodies narrow
toward the ends like jet airplanes. Air
flows smoothly over their feathers while
they fly.
However, a few types of bird cannot fly.
Penguins have paddlelike wings that are
useless for flying. But their wings help
them swim well. Ostriches and similar
flightless birds have small wings and
weak chests. They walk or run
everywhere on their strong legs. Most
other kinds of bird can walk (or swim)
and fly.
Every bird has two legs, two feet, and a
bill. Many birds have a pouchlike area of
the throat called the crop. The crop is
used to store food. Many birds also have
a gizzard, a part of the stomach that
grinds up food. Birds lack teeth, so they
cannot chew their food.
Feathers
Feathers help birds fly and protect them
from water, heat, and cold. Birds rearrange
and clean their feathers regularly.
Most kinds also apply oil to the feathers
from a gland near the tail.Water slides
off the oiled feathers instead of soaking
through. At least once a year birds shed
Birds have different kinds of bills to help
them eat different kinds of food.
BRITANNICA STUDENT ENCYCLOPEDIA Bird 77
their old feathers and grow new ones.
This process is called molting.
Senses
Birds have sharp eyesight. For instance,
an American kestrel flying 100 feet (30
meters) above a field can spot a
grasshopper on the ground below.
However, birds generally have a
narrower range of hearing than humans
do. Their sense of smell is usually not
highly developed.
Behavior and Feeding Habits
Some types of bird live alone most of the
time. Other types are more social. They
may feed, sleep, fly, and nest in groups
called flocks.
Birds use many different sounds to communicate
with one another. For
example, some baby chicks stop moving
when their mother produces a danger
call. Birds may sing to attract mates.
They may also sing to announce that a
certain patch of land belongs to them.
Birds eat a wide variety of foods. Many
types eat insects. Some waterbirds catch
fish. Birds of prey catch many kinds of
animals, including other birds. Some
birds, such as vultures, feed on dead
animals and garbage. Many other types
eat plant material, such as seeds and
fruits.
Reproduction
Most birds breed at least once a year.
Many types build nests for their eggs. A
nest can range from a scrape in the sand
to a cup of twigs and mud to a complex
hanging basket. The female bird lays a
set of anywhere from 1 to 20 eggs,
depending on the species.
Most birds sit on their eggs to keep
them warm. This process is called incubation.
The eggs hatch into young birds
in about 11 to 80 days, depending on
the species. Some young birds can feed
themselves almost immediately. Other
types depend on their parents to provide
their food for a time.
#More to explore
Animal • Dinosaur • Feather
• Migration, Animal • Pet • Poultry
Bird, Flightless
Millions of years ago, all birds could fly.
But as time passed, some birds became
flightless. That is, they lost the ability to
fly, though they still have wings.
An American robin brings a worm to its
hungry young.
78 Bird, Flightless BRITANNICA STUDENT ENCYCLOPEDIA
Why Some Birds Do Not Fly
Scientists do not agree on how some
birds became flightless. One idea has to
do with where the birds lived. The first
flightless birds may have appeared in
isolated places, or places cut off from the
rest of the world. Birds living in these
isolated spots, like islands, found no
enemies. For that reason, they did not
need to fly to stay alive. So, as these
birds evolved, or developed over thousands
of years, they gradually lost their
ability to fly.
Flightless Birds Today
The largest flightless birds are the
ostriches of Africa. Rheas, emus, and
cassowaries are other large flightless
birds. Rheas live in South America,
emus live in Australia, and cassowaries
live in Australia and New Guinea. All
these birds are about 5 feet (1.5 meters)
tall and have very strong legs.
Kiwis and penguins are two kinds of
smaller flightless birds. Kiwis are about
the size of a chicken. They live in New
