I believe the jury is still out on what birds can and cannot do.
Certainly they can navigate to a destination without relying solely on
visual cues, but whether this is magnetic sensing (as some researchers
affirm) or not remains unproven. "attitude flying" is of course a diffent
question - can they stay upright in cloud?

There are probably differences in different types of birds as well. I know
some people who keep exotic birds at home have only to turn off the lights
if they want to catch the bird to put it back in its cage. As soon as it's
dark, the bird will not move. While other birds, obviously, fly at night
regularly.

If birds prefer VFR, they must certainly get in the same situation as
pilots, and wander inadvertently into IMC. But then, we cannot know what
their loss rate is!

GF