ALL ABOUT BIRDS

Modern-day birds do not have any teeth (ancient birds did have teeth). Birds have a tongue, but unlike our tongue, a bird's tongue has a bone in it.
Birds spend most of their time looking for food. Most birds are insectivores (they eat insects). Some birds, like owls and eagles, are carnivores (meat-eaters). Some birds, like the hummingbird, grouse, and Canada goose, are mostly herbivores (plant-eaters). Other birds, like starlings, are omnivores (plant- and meat-eaters). Some birds (like the toucan) are fructivore (fruit-eaters)
Birds mostly use their keen eyesight to find food. They use their beak and their claws to get bugs, worms, small mammals , fish, fruit , grain, or nectar.

Birds play a very important part in the natural control of insects and in the dispersal of seeds. Some birds, like the tiny, nectar-eating hummingbird are important pollinators of some flowering plants. 

Nests and Eggs:

The ostrich lays the largest birds' eggs; their eggs are up to 4.5 x 7 inches (11 x 18 cm) across and weigh 3 pounds (1400 g).

Birds bear their young in hard-shelled eggs which hatch after some time. Some birds, like chickens, lay eggs each day, others (like the maleo) may go for years between laying eggs.
Birds build nests for breeding in trees, on cliffs, or on the ground. Most birds are taken care of by at least one parent until they are able to fly and get their own food. 

Bird	Incubation Period
Chicken	20-22 days
Ostrich	42-50 days
Parakeet (budgie)	27-28 days
Pigeon	14-18 days
Swan	30 days
Toucan	18 days

The incubation period of bird eggs varies from species to species. There's also some variability due to the temperature.
Some birds, like old-world cuckoos and some cowbirds, lay their eggs in other bird's nests. The non-related adult bird takes care of the cuckoo's egg unwittingly. Some cuckoos even kill the other eggs in the nest to insure that their egg gets enough food. 

Migration:
Many bird species migrate to a cooler climate for reproducing and summer feeding, and then return to a warmer climate for the winter. It is unknown exactly how birds are able to navigate accurately, but many people are studying this mystery of how birds know where to fly. 

The Classification of Birds:
Birds belong to the biological class Aves and live virtually everywhere on Earth. Birds are amniotes, animals whose eggs are protected from drying out (a group that includes the mammals, birds, dinosaurs, and reptiles). There are about 9,000 different species of birds, divided into 24 orders and 146 Families. Most birds alive today are Neognathae (a group distinguished by common palate structure). Another, much smaller group, is the Palaeognathae (again grouped by palate structure), which includes the ostrich, kiwi, emu, rhea, and others. 

The Evolution of Birds:
Birds probably evolved from meat-eating (theropod) dinosaurs during the Mesozoic Era, roughly 150 million years ago. Early birds, like Archaeopteryx, had teeth in their mouth and claws on their wings. 

Bird Songs:
Birds sing beautiful and diversified songs. Many songbirds are becoming scarcer every year.
Songbirds have a vocal organ called the syrinx located in the throat. The muscular syrinx has two halves that each vibrate to produce songs, so the bird can sing two notes at a time. To sing, a bird blows air from the lungs through the syrinx. 

Do Bird Have Knees?
Why Do Their Legs Bend Backwards?
Yes, birds have knees (they're often under the feathers and not easily visible), and they bend the same way our knees bend. The part of a bird's legs that bends backwards when it walks is the ankle. 

Heart Rate and Breathing:
In order to fly, birds need a lot of oxygen, which they get by breathing air using lungs. They also need a strong circulatory system, including a powerful heart in order to circulate the oxygen. A bird's heart beats much faster than our heart does. A hummingbird's heart beats about 1,000 times each minute; a human's heart beats about 60-90 times each minute.

Birds breathe using a unique system in which air follows a one-way route through the respiratory system. This system is unlike our lungs, in which the air backtracks where it came from. Their system of respiration (breathing) is very efficient - much more efficient than our system.

Birds have two relatively small lungs (where gas exchange occurs), but the lungs are augmented by bellows-like air sacs (where no gas exchange occurs). These air sacs keep the lungs perpetually inflated (even when the bird is exhaling). Our lungs alternately fill and empty out. The bird's respiratory system takes up 20% of a birds's volume (our respiratory system takes up only 5% of our volume).

In the bird's respiratory system, air first flows through air sacs (located even inside their hollow bones) that direct fresh, oxygenated air into the tube-like lungs (parabronchi, where gas exchange occurs) both when the bird inhales and when it exhales.

This system increases birds' respiratory efficiency and gives them enough oxygen for flight.

Why Can Birds Perch on Power Lines?
Birds can often safely perch on a power line without being electrocuted. For the bird (or other animal) to be electrocuted, a potential difference must exist across two points of the bird's body (its feet in the case of a bird on a power line). When perching on a single power line, there is no potential difference between the bird's feet, so it is safe. If the bird (or other animal) touches two power lines at a time, or one power line and a ground (like a ground wire or the earth itself), the animal would be electrocuted and die. Many large birds (like eagles and vultures) are electrocuted when their wide wings touch a power line and a ground wire at the same time (often while flying in to land on a power line).

This is why it is VERY unsafe to fly a kite near power lines. If the kite gets tangled in the power lines, the kite string acts as a ground, and you can be electrocuted. 

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http://www.enchantedlearning.com/subjects/birds/