Once considered one of the most endangered wild cat species in the world, their population declined by 87 per cent and the number of breeding females dropped by more than 90 per cent between 1985 ...

As part of a global breeding program, the Philadelphia Zoo welcomed an Amur tiger and Amur leopard to aid conservation ...

Other species under consideration for “de-extinction” Passenger pigeon: Once believed to be the most numerous bird in North America, the last passenger pigeon died in a zoo in 1914.

In the 1980s, it was suggested that an extinction should be declared if a species was not observed for 50 years. That seems like a long time, but it wasn’t long enough.