Norfolk Boobook (Ninox novaeseelandiae undulata) got down to a single female in 1986. A male Morepork (Ninox novaeseelandiae novaeseelandiae) was introduced and they successfully bred. The female died in 1996, at the time there were a dozen hybrid birds on the island, and the population is still there. I don't know if that's a win or not, the species is extinct but the genes are still present. The Cromwell Chafer Beetle (Prodontria lewisi) is only found in one 81 hectare reserve and would likely be extinct now without this habitat protection.
I suspected a few more turtles fit the bill -and yes there are. Northern and Southern River terrapin Myanmar roofed turtle McCord's box turtle Golden Headed box turtle Burmese star tortoise Roti Island snake headed turtle Vietnamese pond turtle Chinese Red Necked turtle a few others may make the list in a few more years http://www.iucn-tftsg.org/wp-conten...lition_2018_Top_25+_Turtles_in_Trouble_lr.pdf
The species still survives, it is the island race that has been partly lost due to hybridisation with the nominate form. Natural selection will act upon the hybrid population and there will hopefully be selection for those characters best suited to the island. These hybrid owls will be fulfilling the ecological role of the original race. This is a very important case study that shows that sub-specific substitution is a viable alternative to extinction.
I had a bit of a look at all these species. Fortunately their minimum populations don't seem to have fallen below 500 individuals, and a number seem to be heavily bred in captivity. What happens to those bred in captivity, I shudder to think, as I doubt any are being released into the wild.
Two interesting cases of conservation. While the Norfolk Isl owl's genes persist, is this a success through hybridisation? Difficult one. New Zealand creating a protected reserve specifically for one beetle spp is impressive. The estimated population is 3000, so too large for this purpose.
