Name the bird which can fly backward also

'Group of wolves'is called___________.

Name the "group of Bears"

Name a 'Group of crocodile'

'Group of fishes is called_________.

'Group of dogs' is called_____________

'Group of flies' is called ___________.

'Group of sheeps'is called __________.

'Group of pigs' is called___________.

Which is the largest bird in the world?