What goes up a chimney down, but can't go down a chimney up?

I stand in a field all day with my arms out, and I keep the crows away. What am I?

What has a neck but no head?

What is full of holes but still holds water?

The more you take, the more you leave behind. What are they?

What can fill a room but takes up no space?

What do you call a bear with no ears?