Well: https://reddit.com/comments/8bspee//dx9du3q/

Don't most bird just go to sleep when blindfolded ? Or is it just an idea that got in my mind ?

They don't tend to actually sleep. They do become more docile, because they can't see to fly without risking hitting something.

Thinking about it, it was pretty dumb on my part. I know about hunting birds, I should have thought about that.

> they can't see to fly without risking hitting something.

This sentence makes me wonder: are they docile because it genuinely calms them, or are they entering a sort of helpless automatic panic mode, like "OMFG no escape, can't fly, can't move"?

The latter sounds like the bird is getting a terrifying experience.

Alligators do. Not sure about birds

I considered blindfolding, but from what I gather the protein would be activated merely with the presence of the field.

Looks like the humane way to test, according to the article cited above, is to affix magnets to the eyes/beak to see if it disrupts anything. In any case, in retrospect, I personally feel my suggestion to remove the beak is more cruel than removing the eyes. Both are hideous to contemplate. But, a bird without a beak? That's just a miserable thing to imagine.

The original article suggests that the cryptochrome responsible for magnetic sensing must be stimulated by light to work, and in particular light of the right wavelength.