I think this title is a Blu-ray MOD like The Trouble with Angels that will eventually show up like prior Sony MOD releases. I've seen this kind of quirky not available designation for White Nights and Steel Magnolias just to name a few of these Sony BD MOD releases that came out earlier this year.
I see 'The Trouble with Angels" link on Amazon became active today which means "Birdy" is probably next since both of them are Sony Blu-ray MOD releases for June 25th.