Our Feathered Friends
Earth is home to more than 9,000 different
species of birds. Birds are warm-blooded,
feathered animals of many shapes, sizes, and colors. Some birds live in large
groups called flocks. They spend their entire lives with lots of other birds.
Other species are solitary.
They rarely interact with members of their species. Most birds can fly, and
they rank as the most skilled fliers in the animal kingdom. Being warm-blooded
has helped birds adapt and spread to many kinds of environments. Today, birds
are found on every continent on Earth - even Antarctica where penguins live
happily in temperatures that drop as low as -35°C.
Birds lose their feathers and replace them with new ones. When a bird
loses all its feathers, it is called molting. Every species of bird
molts, even those that can’t fly, like penguins.
©M.Campbell/GLOBIO.org Early Birds
Archaeopteryx was the first bird to evolve. Archaeopteryx had wings
and feathers but also had teeth and claws – features modern birds do
not have. Scientists believe archaeopteryx probably ran and hopped
more than it flew.
©J.Tucciarone (illustration)
Birds are believed to have evolved from
meat-eating dinosaurs that walked on their hind legs about 150 million years
ago. Some of these prehistoric creatures had feathers and wings and could
fly. Some had features that were very different from those of modern
birds. One of the first birds, called archaeopteryx (ar-key-OP-ter-iks), had
teeth in its beak and claws on its wings. It probably ran and hopped instead
of flying. As birds continued to evolve, their teeth and claws disappeared.
Modern birds do not have teeth or claws.
Coming Out of Their Shells
Birds begin life as eggs. Most birds
lay their eggs in a nest. Incubation time
varies for each species. Baby birds cannot fly immediately after hatching.
Many species do not have feathers as newborns. However, the babies of species
that spend a lot of time on the ground - ducks, chickens, and ratites -
are covered in fuzzy feathers and can run or swim almost immediately.
Several Sets of Feathers
Young birds grow special juvenile feathers
before they grow their adult feathers. Often, a young bird will go through
several sets of feathers before it is an adult. Even adult birds molt,
that is, they lose old feathers and replace them with new ones. Some
birds do not become adults for several years while others become adults in
a matter of months.
A kiwi is a small flightless bird that lives in New Zealand. This
amazing bird lays a very large egg, given its body size. A 1,800g kiwi
can lay a 450g egg. That’s a big baby! Here you can see
how much space the egg takes up when it’s inside the kiwi.
©Otorohanga Zoological Society
Spreading Their Wings
An adult bird no longer depends on its parents. It is ready to look for a
mate and sometimes a territory of its own. Some birds, like swans, mate
for life. Others may have many mates throughout their lives. Birds like
parrots and their relatives may live very long lives, between 40-100 years. Other
bird species live shorter lives. These birds often have more chicks than
birds that live longer.
Bird Bodies
Feathers are the one characteristic that all birds share.
Click on the bird picture below to find out more.
Adapted for Just About Anywhere
Bird adaptations are
often linked to the environment they live in. Vultures are a type of
bird called a scavenger. Vultures are not fussy eaters and will eat many kinds
of carrion.
Other birds, like the finch species that live in the Galapagos Islands, have
specific niches.
They do not directly compete with the other finch species. Some eat seeds,
while others eat insects.
No Teeth, No Problem!
Since birds have no teeth, they must break or tear their food and then swallow
the pieces. The food is first “chewed up” in a special organ
called the gizzard. Birds
sometimes swallow tiny stones. The stones remain in the gizzard and help grind
the food. The ground-up food then travels to the stomach to be digested.
In many birds, the food is first stored in a pouch called a “crop” part
way between the throat and stomach. This helps birds swallow a lot of
food fast so they can fly to a safer place to digest it.
Flying is a Great Way to Travel
Many birds migrate or travel to a warmer climate during the cold winter
months. Birds like geese and ducks migrate in large groups called flocks.
Each night the whole group stops to eat and sleep.
©G.Ellis/GLOBIO.org
There are many bird species that migrate to
a new environment during parts of the year. These migrations may cover relatively
short distances or very great distances. Most migrating bird species
move to cooler climates in summer. During this time, they reproduce.
They migrate to warmer climates in the winter. Arctic terns have the
longest migration. They migrate from the Arctic to the Antarctic and back every
year. That’s more than 32,000
km! Scientists are still trying to discover exactly how migrating
birds know where to go every year.
Not All Birds Fly
All birds have wings and feathers, but not all birds fly. Penguins, for example,
cannot fly, but they are excellent swimmers. They have special oily feathers
that make them waterproof. Ostriches and emus are two land birds that do not
fly. They use their long legs to speed away from predators.
Most bird species that cannot fly are found on islands. Scientists think that
over time these birds lost the ability to fly because they no longer needed
to fly away to find food or escape from predators. Many of these island
birds are now endangered.
They now have predators such as cats and rats. These animals arrived with people
and now attack the flightless birds and their nests.
Giving Plants a Lift
Birds fill many important roles in their
environments. Birds and plants are connected in many ways. Hummingbirds,
honeycreepers, and sunbirds have long beaks specially adapted for reaching
deep inside flowers. As they search for sweet flower nectar, they help pollinate flowers
and other plants.
Many birds are responsible for transporting seeds from one place to another.
A few even play a role in helping the seeds germinate and
grow. In the tropics, toucans, hornbills, and parrots open and eat many
kinds of fruits. As the birds fly off with the fruit, the seeds are scattered
to new locations. This helps new trees grow far from the parent tree.
©GLOBIO.org Dancers and Decorators
Many birds have special or unusual behaviors.
Often these behaviors are part of the mating ritual. The male bowerbirds
of Australia make elaborate structures out of brightly colored objects they
have collected and arranged. They do this to get females to mate with them.
Some birds do a special dance. The blue-footed boobies of the Galapagos Islands
wave their big blue feet to attract a mate.
Bowerbird males make very fancy structures to attract females. Some
collect things that are a certain color or that are shiny.
©G.Ellis/GLOBIO.org
The cuckoo bird lays its eggs in other birds’ nests so that it doesn’t
have to use energy raising chicks. The unknowing parent of the other
bird species feeds and cares for the baby cuckoos even though they do not belong
in the nest.
Feathers, Food, and Beautiful Songs
People use birds for many things. Their feathers are used for decoration
and for making warm clothing and pillows. People all over the world
eat different birds. People hunt wild birds such as pheasants and grouse. Chickens,
ducks, and ostriches are some of the birds that are raised for food and feathers.
©K.Feng/GLOBIO.org
People rely on birds for many things. Birds
such as pigeons, chickens, and ducks provide food for people. Some people keep
birds as pets. Others enjoy bird watching out in the wild. Birds in some
cultures are even thought to signal when earthquakes are coming. Birds also
are very important in maintaining environmental balance. Decreases in the bird
population serve as signals that problems like pollution and loss of habitat
are changing the world we live in.
Bird Conservation
Many bird species are endangered as a result
of human activities. For example, people hunted the giant moa, which stood 3.7
m tall, to extinction.
Peregrine falcons almost became extinct because of the pesticide DDT. This
pesticide entered the food
chain and eventually ended up in the bodies of the falcons. It caused
their eggs’ shells to be thin and brittle. Because of this, many eggs
broke before it was time for the chicks to hatch. A ban on DDT, captive
breeding programs, and habitat conservation
have helped peregrine falcons around the world make a successful recovery.