Yes, I agree for bif I use manual exposure. First before shooting I use spot metering usually on a light gray barked tree or a perched bird of about the same color. I then check once in a while to see if the light conditions are the same throughout the shooting time frame.
Shooting bif against a white cloudy sky has not been very successful for me. Usually not enough contrast to get good sharp focus, blue sky or a background of vegetation is better for af for me.