The Arabian oryx extinct in the wild was successfully bred in captivity and reintroduced into an Oman reserve.

ECONOMIST: From zoo cage to modern ark

The Suffolk Wildlife Trust began introducing fen raft spiders, which had been bred in captivity, to Castle Marshes reserve near Beccles in 2010.

BBC: Rare fen raft spiders breeding in Suffolk

The tiny snails, which grow up to 2.5cm in length, are being bred in captivity in strict conditions at a temperature of 20-24C with a humidity of about 70%.

BBC: Partula tree snail

The endangered squirrels, being bred in captivity at the Welsh Mountain Zoo at Colwyn Bay, are set to be reintroduced into the forest, with the hope that up to 300 will make their home there.

BBC: NEWS | UK | Wales | North West Wales | Tree-felling 'to preserve dunes'

But they're endangered, so it's pretty remarkable that the Nashville Zoo successfully bred one in captivity.

CNN: Apparently This Matters: Baby Baird's tapir

The foxes bred well in captivity, but early releases were soon snapped up by golden eagles, so the park service had to first relocate the goldens to the mainland and then reintroduce the balds, carefully stewarding their eggs until the channel cleared of DDT.

FORBES: Report: Endangered Species Act Works