Both species were doomed to extinction at the point they were housed at the zoo. The passenger pigeon only bred in large flocks and by the time everyone realized they were on the decline, there were no more large flocks.
The zoo at this point were just recording the last survivors for posterity's sake.
> The passenger pigeon only bred in large flocks and by the time everyone realized they were on the decline, there were no more large flocks.
So do penguins, gulls and terns, yet they can be bred in zoos. Also, the big colonies of the passenger pigeon mostly like where a phenomenon of the 19th century (possibly human induced), the effective population size of the species has been shown to have been in the hundreds of thousands range.
Oh, and the Carolina parakeet was bred in zoos, even in Europe. Unfortunately they weren't that consistent back then yet.
Sure, but is that because we cannot do it or because we don't really want to do it? I'd argue that bringing back a the elephant bird would be more exciting (from a 'cool' perspective and scientifically) then bringing back a pigeon or parakeet. There are already dozens (or more?) of species of both of those alive today, with some very close relatives included.
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.
The idea of bringing something old world into current is compelling, definitely morbid in some sense, and primal.
Yeah, not a good mix, but what can I say? This is a want to see happen. I am likely to regret it, but maybe, just maybe it could be a good thing. Somehow.