I'm lazy. Instead of getting a fresh post, you get my lecture that I delivered to nobody in particular in the #nerdparadise chatroom a few months back, which also happens to be a forum post I made about thirty seconds ago (Today's Saturday. Pretend this update happened on a Friday, okay?).
I'm really interested in cloning extinct birds (and, for that matter, most creatures that come from a hard-shelled egg). The geirfugl, the dodo, the Rodrigues solitaire, the passenger pigeon, the moa, the California condor (there are fifty-something left...it may not be extinct but it needs all the help it can get), and all sorts of dinosauranoids.
Anyway. There are lots of reasons why we have yet to bring back extinct bird species. There are two extremely large reasons.
The first is that this reintroduced specimen will have no parental figures and, consequently, much of its behaviour will be drastically different than the original species and it may not know how to act in certain situations that would doom the creature in the wild. This is unavoidable unless avian psychologists make some amazing breakthroughs soon.
The second reason, which is the one I understand far less, concerns the eggs themselves. As far as I know, not a single avian has been cloned, because the eggs are a pain to deal with. Every species' eggs are slightly different, and many extinct animals (like the dodo and Rodrigues solitaire) have no living relatives close enough to act as substitute-egg-donors. Then there's the issue of actually inserting the extinct animal's genetic information into the nucleus of the egg cell before it starts to form a morula. Then there's the issue of successfully implanting the egg in a suitable foster parent (because, really, there's no way in hell you're going to have any modern bird lay a dinosaur egg) who will also care for the young hatchling if need be.
The only solution I can think of for issue #2 would be to invent several new substances that can act as artificial albumen, yolk, shell, and other stuff that goes into eggs. It would have to be pliable at times, to allow for gene-insertion as well as readjusting the levels of the fluids and nutrients in the egg, but it would also have to be rigid to mimic a proper egg. I dunno. Someone else can figure that one out.
Recommended reading: Digging for Dodos by Ian Parker, New Yorker Magazine, January 22, 2007. The link I provided is not the full text; it continues for many more pages. While you're at it, you might as well read Jurassic Park and The Lost World by Michael Crichton.
