How to repair small area of damaged/loose plywood sheathe on roof?
Check with your local/state laws about moving birds/wildlife first.  I know in my area its illegal to move bats during certain times of year.  Now birds aren't bats but bats also make noises that could sound like a bird to an untrained ear.  Even if its birds, a lot of birds are protected here in the US so similar laws may apply. For bats they make 1 way doors that you attach to allow them exit but not come back in.  Put it there for a while to let all the critters out and then remove it in favor of a permanent fix.

Next, if you are looking for a quick fix that should last until the next time you replace the roof, you could always use some spray foam.  They make it in all sorts of colors or you can paint it to be the least obvious.

However, you really need to find the source of the leak that caused the plywood to rot and the curling in the first place, or else you will likely end up with just a bigger mess to deal with.