Two of the most enthusiastic (and entertaining) feeders I ever dealt with were a pair of loggerhead turtles at an aquarium where I volunteered. The brothers, the size of a soup plate each, would lunge towards the water's surface when they'd see me, beating their flippers frantically and pushing each other out of the way as I offered pieces of fish impaled on the end of a fork.
So, a small number of those endangered turtles - small in overall number, large compared to the number of other turtles that actually survive the day - are removed from the beach and taken into captivity. They are reared to a certain size - at least until they are too big for most predators to tackle - and then released. Essentially, it's allowing these animals to skip the part of life when most of them tend to, well, die, and then reenter the population with a better chance of becoming breeding adults. It's called headstarting.
Headstarting allows scientists and conservationists to manipulate a population so that more members escape the vulnerable phase and are able to reproduce. It's similar to captive breeding for reintroduction, but differs in that the only members of the population that are ever in captivity are the young ones - the adults are left loose to breed. This works well for species that might prove difficult to breed in captivity, such as ones with very specific environmental requirements, or with food requirements that are too difficult to replicate in a zoo. Or, say, large marine turtles.
The downside of headstarting, however, is that it only works on a select group of animals. Specifically, it works with animals that don't require much in the way of parental care. Fish and invertebrates, reptiles and amphibians all fit that bill, and all require very little learning to survive. A baby Komodo dragon or a newly hatched Chinese alligator are all born hunters, ready to fend for themselves once they hatch. It's not too difficult to see, then, how a reptile egg, hatched in a zoo, could then be turned loose and able to survive.
Mammals and birds, in contrast, are not born so ready-to-go. They require a mother, sometimes a father, sometimes even siblings or an extended family group, to teach them how to survive - how to hunt, how to feed, how to avoid danger. A whooping crane chick needs someone to teach it how to migrate. A thick-billed parrot chick needs to learn how to open pine cones. A mandrill needs to learn how to navigate the complex social structure of a primate.
I moved on from the aquarium before the turtles had reached the point at which they would have been deemed ready for release. Once they were sent out, more young turtles would be brought in to be raised in their place. I like to think that they were released and are swimming out in the sea, along with the very few of their brothers and sisters that survived the carnage of their birthday. Maybe, someday they'll have their own offspring, which will spend some time in a tank before returning to the ocean.