What makes a bird, a bird?

Birds are descendants from Bipedal; which are the Reptilian like dinosaurs from Jurasic Period. Ultimately, birds have many characteristics which are similar to Reptiles.

1. Their legs are covered by scales similar to reptile bodies
2. Birds are vertebrates
3. Birds also lay eggs which has as thick shell and a amniotic sac

But what makes bird, a bird is some unique features it possesses. Feathers, powerful wings, lightweight body, hollow bones, warm blood, amazing respiratory system and a comparitively large Heart; helps the birds FLY.

1. Feathers
The most important role of Feathers is to to give protection. Feathers also helps them to stay dry and warm. Feathers also play an important role in flying. And hence birds take very good care of their feathers.

Preening and Molting
Feathers also act as a Raincoat. Many birds possesses a Gland at base of their tail which produces OIL. Birds spread this oil to their feathers using their beaks. This process is called as Preening. Oil layer makes the feathers Waterproof and it also prevents the growth of fungi. Birds like Cormorants; does not have this Oil Gland in their body. And hence after being to water these birds need to dry their wings by spreading out wide. Look at the Cormorant in left image who is drying his wings in a
sunshine @ Khadakwasla Dam, Pune. When feathers wear out, birds replace them by molting. Molting is the process of shedding old feathers and growing new ones. Most birds shed their feathers at least once a year.

Types of Feathers
Birds have two main type of feathers. Down feathers are fluffy feathers that lie next to a bird’s body. These feathers help birds stay warm. When a bird fluffs its down feathers, air is trapped close to the body. Trapping
air keeps body heat near the body. Contour feathers are stiff feathers that cover a bird’s body and wings. Their colors and shapes help some birds attract mates. Contour feathers have a stiff central shaft with many
side branches, called barbs. The barbs link together to form a smooth surface. This streamlined surface helps birds fly.

2. High-Energy Animals
Birds need a lot of energy to fly. To get this energy, their bodies break down food quickly. This process generates a lot of body heat. In fact, the average body temperature of a bird is 40°C which is three degrees warmer than humans. Birds cannot sweat to cool off if they get too hot. Instead, they lay their feathers flat and pant like dogs do. Left image is of the Swan Goose which are the migratory birds. They fly long distances in winter; and required a high energy to fly.


3. Fast Digestion
Because birds need a lot of energy, they eat a lot. Hummingbirds need to eat almost constantly to get the energy they need! Most birds eat insects, nuts, seeds, or meat. These foods are high in protein and fat. A few birds, such as geese, eat grass, leaves, and other plants. Birds have a unique digestive system to help
them get energy quickly. Modern birds don’t have teeth, so they can’t chew. Instead, food goes from the mouth to the crop. The crop stores food until it moves to the gizzard. Many gizzards have small stones inside. These stones grind up the food so that it can be easily digested in the intestine. This grinding action is
similar to what happens when we chew our food.

4. Flying
Most of the birds can fly. Even flightless birds, such as ostriches, have ancestors that could fly. So, it is not surprising that birds have many adaptations for flight. For flying; birds are required to have the reduction in weight and increment in power and the most obvious characteristic related to flight is the wings. Birds have very lightweight bodies. And they have powerful flight muscles and fast heart beats. The fast heart beats helps birds get plenty of oxygen - rich blood to the flight muscles.


5. Getting off the Ground
How do birds overcome gravity to fly? Birds flap their wings to get into the air. They keep flapping to push themselves through the air. They are able to stay in the air because their wings cause lift. Lift is an upward force on a bird’s wings. As a bird flies through the air, some of the air is forced over the top of its wings. Some air is forced underneath the wings. Because the bird’s wings are curved on top, the air on top has to move farther than the air underneath. So, the air on top moves faster than the air underneath. The faster moving air on top creates an area of low pressure. The slower moving air underneath creates an area of high pressure and pushes the wing up. This upward force that acts on wings is called lift. Lift is affected by flying speed and by wing shape. The faster a bird flies, the greater the lift. Also, the larger the wing is, the greater the lift. Birds with large wings can glide for long distances.

6. Vision
Vision is the most highly developed sense in birds. Bird Vision is superior than any any animal. Some birds from famiy Birds Of Prey; has even larger eyes than humans. Larger eyes obviously more sharper and clean images; this helps birds to identify the movings objects very efficiently. Position of eyes though differ from one species to another. Birds of Prey category birds usually has eyes pointing towards front. This helps locate the prey from very far in the air. Ostrich has larger eyes which helps spot the preditors from far.


7. Raising Baby Birds
The way that birds reproduce is similar to the way that reptiles reproduce. Both birds and reptiles lay amniotic eggs in which there is a growing embryo. But unlike most reptiles, birds must keep their eggs warm for the embryos to live and grow.


Nests
Most birds build nests in which they lay their eggs. Birds keep their eggs warm by brooding. Brooding is the act of sitting on eggs and using body heat to keep them warm. Birds sit on their eggs until the eggs hatch.
For some birds, such as gulls, the job of brooding is shared by both males and females. In many species of songbirds, the female broods the eggs, and the male brings food to the brooding female. In a few species, the male broods the eggs.


Precocial and Altricial
Some birds, such as chickens and ducks, are active soon after they hatch. These active chicks are precocial. Precocial chicks are covered with downy feathers. As
soon as they can stand up, the chicks follow their parents around. These chicks
depend on a mother for warmth and protection, but they can walk, swim, and feed
themselves. Some birds, such as hawks and songbirds, are weak and helpless for a
while after hatching. These weak chicks are Altricial. When they hatch, they have no feathers and their eyes are closed. They cannot walk or fly. Their parents must keep them warm and feed them for several weeks.