to look out for danger, or/and to see their surroundings, or/and to talk to other budgies in their kinda way. i think.
If your budgies are used to being indoors, and if you do not live in a warm climate, they should not be moved to an aviary. Cold winters are deadly for budgies.
Fly, walk or climb.
To "Dike" is to move back suddenly.
Orthodox Jews always wear a head-covering (kippay/yarmulkah, or a hat).
If gravity suddenly disappeared, the moon would fly out into space in a straight line. If the moon suddenly stopped moving it would fall straight into Earth.
It gives better stability to keep the body (and head) still while driving. Your eyes would not be able to focus on the road and other cars if your head were to suddenly move.
dart
Inertia
Smile always smile and tilt your head a little bit smile at the crowd ALWAYS
Because it doesn't feel comfortable when you move your head close to their's.
jerk
Zoom.