However, reintroducing corncrakes and mountain chicken frogs to Cambridge and Monserate is a very different prospect to returning Sumatran tigers back to the wild or lowland gorillas or any other of their endangered species that are not so straight forward. I've looked but can't find any evidence they are working on or close to releasing any gorillas, big cats or any other of the species that have been affected by multiple mostly man made issues?
What makes you think that the only species being worked on, or which have been worked on in the past, are those which have *not* been affected by "multiple mostly man-made issues"?
Moreover, what makes you think that those taxa that have been reintroduced *are* straightforward? It can't be a case of assuming that small = straightforward and large = not so straightforward, as a number of the species which have benefited from reintroduction programmes are very large indeed.
To discuss only those taxa already mentioned within this thread:
Black-footed Ferret - decline and extinction in the wild was due in large part to extermination programmes aimed by man at their primary prey item, the prairie dog, along with conversion of prairie habitat to agricultural cropland.
Arabian Oryx - hunted to extinction in the wild by man.
Partula Snails - accidental introduction of African Land Snail into Tahiti by man led to an attempt at extermination through the deliberate introduction of Florida Rosy Wolfsnail, which preferentially targeted the native Partula snails - entirely wiping out many species and rendering others extinct in the wild.
Mountain Chicken - combination of chytrid fungus brought to the West Indies by man, extremely high levels of hunting by man and habitat loss due to volcanic eruption and expansion of human activity has brought this taxon to the brink of extinction.
Mauritus Kestrel - combination of habitat loss due to deforestation, invasive predatory species introduced by man, and DDT poisoning brought this taxon to a world population of 8 by the 1970's.
Pere David's Deer - original cause for decline unclear, probably habitat loss. Final individuals outside captivity killed and eaten in 1900.
Przewalski's Horse - brought to extinction in the wild through hunting and habitat loss.
Wisent - brought to the brink of extinction by habitat loss and heavy hunting by man.
Corncrake - although still commonplace in their stronghold of Asia, significant declines across Western Europe due to habitat loss relating to the industrial revolution and the decline of traditional agriculture.
Kihansi spray toad - brought to extinction in the wild due to habitat loss relating to the construction of a dam, with chytrid introduced by man posing a complicating factor.
Red Wolf - habitat loss and persecution by man brought this taxon to extinction in the wild.
American Bison - extreme habitat loss and hunting by man brought this taxon to the brink of extinction.
Californian Condor - extreme habitat loss, hunting and poisoning through use of DDT exterminated this taxon in the wild.
Black Robin - introduction of invasive predators brought this taxon to an effective wild population of a single pair.
I accept zoos are doing more conservation than I thought but how do we measure it's effectiveness if no species are being returned to the wild?
As we have already discussed, species are being returned to the wild - and as such the question you pose is irrelevant - or is this a case of
"the only species that matter to me are the big-name flashy ones" perchance?