Excuse me, expert, why do I shoot birds with Nikon D5?

This is because the surround exposure or HDR function is turned on. The principle of this function is to combine several photos taken continuously into one to get a photo with both highlights and dark parts. Because it is a combination of several photos, you will see the afterimage of the subject's movement, which is not suitable for shooting the subject. By default, this feature is off.

The solution is simple, just turn it off in the settings.