What is the function of syrinx in the birds?

Function of amnion in birds is

What is the function of hairy coat in most mammals , blubber in whales and seals and feathers , birds ? How do these animals regulate their body temperature ?

What is the sound -producing organ of birds?

What is the sound producing organ of birds?

What is the sound producing organ of birds

What is the scientific reason behind bird's migration?

What is the number of air sac present in bird?