Birds have several defining characteristics including feathers, wings, a beak without teeth, and laying eggs. Feathers come in different types and aid in flight, warmth, and attracting mates. Wings vary in shape between species and are adapted for different environments. Beaks also vary in shape depending on a bird's diet. All birds lay eggs and most species work together to care for offspring. Birds have lightweight skeletons with hollow bones to enable flight, though some flightless birds have heavier bones.

1. English
Birds’ beauty
6/18/2014
Sehrish shahid

2. Contents
 Definition of birds:
 Characteristic of birds:
Definition of birds:
A bird is a warm blooded member of the Aves class,
which has feathers, a beak, no teeth, wings and
bears young in eggs.
Major Characteristics of Birds
 Feathers
Feathers are the defining characteristic of Aves, found on every
living species of bird and no other class of animal. Feathers are
made of keratin, the same substance that forms hair and nails in
other animals and are highly modified scales. Feathers are critical
not only for flight but also for warmth and protection against the
elements -- and in many species, for males to attract mates. Soft,
fluffy downy feathers help keep birds warm, contour feathers
streamline birds’ bodies and aid in flying, and flight feathers on
wings and tail give the bird loft. Birds shed, or molt, old feathers
once or twice each year, depending on the species.

3.  Wings
All birds have wings, although not all birds fly. Nor are wings
confined to Aves; bats are flying mammals and most insects
have wings. Birds' bodies are beautifully designed for flight,
with strong chest muscles and just enough curve to their wings
to provide lift. Differences in wing shape provide different
advantages to the various bird species. The narrow, sharp-
tipped wings of the falcon provide speed; albatrosses soar high
on wings much longer than they are wide. Most songbirds have
elliptical, evenly shaped wings that facilitate quick, small
movements in the tight spaces of their tree homes. Swimming
birds, such as penguins and puffins, have flipper-shaped wings
that propel them rapidly and gracefully through water.
 Beak

4. All birds have beaks, or bills, made of a bony core surrounded
by a thin layer of keratin. Birds do not have true teeth, but
many species have tomia -- sharp ridges along the edges of
their beaks. Birds do not chew food but grind or rip it into
pieces small enough to swallow. The shape of a bird's beak
indicates the bird's general diet. Meat-eaters like hawks and
owls have sharp, hooked beaks for ripping and tearing. Strong,
cone-shaped beaks help seed eaters break through shells.
Ducks and geese have broad, flat beaks for straining food out
of the water.
 Eggs

5. All birds lay eggs, some very colorful or covered with spots.
Eggs are not unique to birds, of course, as fish, reptiles,
amphibians and insects also lay eggs. A bird egg has a hard
shell made mostly of calcium and a layer of hardened mucus.
Inside the egg, the developing embryo receives nutrition from
the yolk and the albumin, the egg white. Most birds construct
nests to protect their eggs, and then care for the eggs and the
hatchlings. The majority of bird species are devoted parents; in
most cases, both male and female care for young.
 Skeleton
Most birds have lightweight skeletons with hollow bones. This
keeps them light enough for flight. Many fused bones,
including the collarbones or wishbones, make birds’ skeletons
rigid in comparison to mammals'. This helps brace the birds'
wings during flight. Their sternums, or breastbones, are large,
providing sturdy attachment points for powerful wing muscles.
Flightless penguins have heavy bones filled with marrow,
helping them to survive in their freezing home range. Ostriches
have heavy, solid bones in their legs, helping the birds run and
defend themselves with powerful kicks.