Re: how many G forces can a bird withstand in a dive or swoop ??

I don't know if anyone has measured the maximum acceleration
that a bird can tolerate, but it's easy to estimate 
the peak accelerations during normal flight.

I use the expression for acceleration during circular motion
A = V^2/R where V is the velocity and R is the turning radius.
Typical values for a bird in flight are V=20 mph
and R=4 feet. This gives A=6 g's (where 1 g is the 
acceleration due to Earth's gravity).

The US Air Force has determined that jet pilots will pass 
out at 10 g's, so this probably isn't too far off for
large birds.