Sealing cracks? Pics added.

[Hangin Wit My Peeps]

I agree with adding the board across rather the caulking it...I don't think the caulk would work...to wide of an area i would think too. Good luck.

 

[dixygirl]

Just nail a 2x4 or even just a 1x4 strip over the slit. It would look like corner trim.

PS if any nails poke through to the other side, hammer them flat so they don't injure the birds.
Good luck with that, it is a simple repair.