Confusion reigns supreme!

Q: What features place birds in Class Aves and not Class Mammalia?

Birds have specialised pelvic muscles.
Birds have feathers, just like mammals.
They have the ability to singing in a way of calling other organisms (birds).
Birds do not bare an alive bird after reproduction.
Birds do not necessarily consist of fur or hair.
Birds give birth to their young in the form of egg shells.
The feathers of a bird act as the hands.
Since birds do not have mammary glands they can not feed their young ones.
Feathers can be regenerated if they are disturbed or broken.
Birds can fly and walk at the same time.
Birds do not give birth to live animals.
Built for flight not pedal.
They do not show any bipedalism, which is displayed by all other creatures in the class mammalia.
Although birds lay eggs, have parental care and have hair they are placed in the class Aves because they can fly (full answer for 10 marks)
They consist of a beaker used for feeding.
They consist of feathers for flying, as well covering body to prevent body temperature inside body.
Aves have beaks instead of jaws and wings are present, which is not seen in Class Mammalia (except in duck billed platypus)
They are not underwater animals.
Birds do not have tits to feed their young with milk.
The feathers are made of retina.
The class Aves include endothermic, where mammals are ectothermic.