[patall]

From what I have heard, there are a number of challenges connected here that have to do that birds are usually not a model organism and we therefore lack certain techniques (and knowledge) on how to handle their cells (especially stem cells) in a laboratory (Not surprising since there is not much medical and therefore financial interest in doing so).

The reason why researchers go for those relatively boring species is their boringness: there are closely related species from which you can borrow cells (and eggs) which you than modify. There is no such thing for a huge (another cost factor) animal with no close relative left.