What type of fertilization occurs in birds?

The presence of feathers and the power of flight are characteristic features of:

Which of the following birds cannot fly?

Identify the correct statements regarding class $Aves$.
$I$. Forelimbs are modified into wings and hindlimbs are modified for walking and swimming.
$II$. Heart is completely four-chambered.
$III$. They are homeotherms.
$IV$. They are oviparous and development is direct.

Preen glands occur on

Which of the following is a flightless bird?