Two non-aviation questions

"Ramapriya" wrote in message
m...
1. If the principles of flight are universally applicable, why is it
that birds don't stall or spin? I wonder especially because I'm sure
I've seen some gulls hover in mid-air doing pretty much nothing except
having their wings spread!

Some kinds of birds stall all the time, they just don't spin since they
recover immediately. Watch swifts or swallows feeding, or harriers hunting.
They continuously stall, then recover.

Gulls can't hover, they just fly forward the same speed as the approaching
wind. Kestrels can hover, they do it by adjusting the angle of attack and
thrust. Hummingbirds can, of course, hover. In fact, they can fly backwards.